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  • 101
    Electronic Resource
    Electronic Resource
    Polarized forward-backward asymmetries of leptonsin $B_s \rightarrow \ell^ + \ell^- \gamma$ decay (2005)
    Springer
    The European physical journal 40 (2005), S. 505-514 
    Details
    ISSN: 1434-6052
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. Polarized forward-backward asymmetries in the $B_s \rightarrow \ell^ + \ell^- \gamma$ decay are calculated using the most general, model independent form of the effective Hamiltonian, including all possible forms of interactions. The dependencies of the asymmetries on new Wilson coefficients are investigated. The detectability of the asymmetries at LHC is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1140/epjc/s2005-02150-0
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  • 102
    Electronic Resource
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    Realistic neutrino masses from multi-brane extensions of the Randall-Sundrum model? (2005)
    Springer
    The European physical journal 40 (2005), S. 539-554 
    Details
    ISSN: 1434-6052
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. Scenarios based on the existence of large or warped (Randall-Sundrum model) extra dimensions have been proposed for addressing the long standing puzzle of the gauge hierarchy problem. Within the contexts of both those scenarios, a novel and original type of mechanism generating small (Dirac) neutrino masses, which relies on the presence of additional right-handed neutrinos that propagate in the bulk, has arisen. The main objective of the present study is to determine whether this geometrical mechanism can produce reasonable neutrino masses also in the interesting multi-brane extensions of the Randall-Sundrum model. We demonstrate that, in some multi-brane extensions, neutrino masses in agreement with all relevant experimental bounds can indeed be generated but at the price of a constraint (stronger than the existing ones) on the bulk geometry, and that the other multi-brane models even conflict with those experimental bounds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1140/epjc/s2005-02165-5
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  • 103
    Electronic Resource
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    Confinement from new global defect structures (2005)
    Springer
    The European physical journal 40 (2005), S. 531-537 
    Details
    ISSN: 1434-6052
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. We investigate confinement from new global defect structures in three spatial dimensions. The global defects arise in models described by a single real scalar field, governed by special scalar potentials. They appear as electrically, magnetically or dyonically charged structures. We show that they induce confinement, when they are solutions of effective QCD-like field theories in which the vacua are regarded as color dielectric media with an antiscreening property. As expected, in three spatial dimensions the monopole-like global defects generate the Coulomb potential as part of several confining potentials.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1140/epjc/s2005-02168-2
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  • 104
    Electronic Resource
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    Dispersion of incoherent spectral features in systems with strong electron-phonon coupling (2005)
    Springer
    The European physical journal 43 (2005), S. 11-18 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. We study (inverse) photoemission from systems with strong coupling of doped carriers to phonons. Using an adiabatic approximation, we develop a method for calculating spectra. This method is particularly simple for systems where the electron-phonon coupling can be neglected in the initial state, e.g., the undoped t-J model. The theory then naturally explains why the electron-phonon coupling just leads to a broadening of spectra calculated without electron-phonon coupling, without changing the dispersion. This is in agreement with recent angle-resolved photoemission spectroscopy (ARPES) on undoped cuprates, and it supports the interpretation in terms of strong electron-phonon interaction. The theory also shows that for systems with strong electron-phonon coupling in the initial state, the result cannot in general be related to the spectrum obtained without electron-phonon coupling.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1140/epjb/e2005-00022-x
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  • 105
    Electronic Resource
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    Electronic structure of the Sr0.4Ca13.6Cu24O41 incommensurate compound (2005)
    Springer
    The European physical journal 43 (2005), S. 29-37 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. We extracted, from strongly-correlated ab-initio calculations, a complete model for the chain subsystem of the Sr0.4Ca13.6Cu24O41 incommensurate compound. A second neighbor t-J+V model has been determined as a function of the fourth crystallographic parameter τ, for both low and room temperature crystallographic structures. The analysis of the obtained model shows the crucial importance of the structural modulations on the electronic structure through the on-site energies and the magnetic interactions. The structural distortions are characterized by their long range effect on the cited parameters that hinder the reliability of analyses such as BVS. One of the most striking results is the existence of antiferromagnetic nearest-neighbor interactions for metal-ligand-metal angles of 90○. A detailed analysis of the electron localization and spin arrangement is presented as a function of the chain to ladder hole transfer and of the temperature. The obtained spin arrangement is in agreement with antiferromagnetic correlations in the chain direction at low temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1140/epjb/e2005-00024-8
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  • 106
    Electronic Resource
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    Bulk mediated surface diffusion: non Markovian desorption with finite first moment (2005)
    Springer
    The European physical journal 43 (2005), S. 65-71 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. Here we address a fundamental issue in surface physics: the dynamics of adsorbed molecules. We study this problem when the particle’s desorption is characterized by a non Markovian process, while the particle’s adsorption and its motion in the bulk are governed by a Markovian dynamics. We study the diffusion of particles in a semi-infinite cubic lattice, and focus on the effective diffusion process at the interface z = 1. We calculate analytically the conditional probability to find the particle on the z=1 plane as well as the surface dispersion as functions of time. The comparison of these results with Monte Carlo simulations show an excellent agreement.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1140/epjb/e2005-00028-4
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  • 107
    Electronic Resource
    Electronic Resource
    Dielectric resonances of ordered passive arrays (2005)
    Springer
    The European physical journal 43 (2005), S. 81-92 
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    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. The electrical and optical properties of ordered passive arrays, constituted of inductive and capacitive components, are usually deduced from Kirchhoff’s rules. Under the assumption of periodic boundary conditions, comparable results may be obtained via an approach employing transfer matrices. In particular, resonances in the dielectric spectrum are demonstrated to occur if all eigenvalues of the transfer matrix of the entire array are unity. The latter condition, which is shown to be equivalent to the habitual definition of a resonance in impedance for an array between electrodes, allows for a convenient and accurate determination of the resonance frequencies, and may thus be used as a tool for the design of materials with a specific dielectric response. For the opposite case of linear arrays in a large network, where periodic boundary condition do not apply, several asymptotic properties are derived. Throughout the article, the derived analytic results are compared to numerical models, based on either Exact Numerical Renormalisation or the spectral method.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1140/epjb/e2005-00030-x
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  • 108
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    On the properties of cycles of simple Boolean networks (2005)
    Springer
    The European physical journal 43 (2005), S. 115-124 
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    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. We study two types of simple Boolean networks, namely two loops with a cross-link and one loop with an additional internal link. Such networks occur as relevant components of critical K=2 Kauffman networks. We determine mostly analytically the numbers and lengths of cycles of these networks and find many of the features that have been observed in Kauffman networks. In particular, the mean number and length of cycles can diverge faster than any power law.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1140/epjb/e2005-00034-6
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  • 109
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    Mean field theory and geodesics in general relativity (2005)
    Springer
    The European physical journal 43 (2005), S. 143-154 
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    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. It is proven that all geodesics in a mean gravitational field can be interpreted locally as the averages of geodesics in the unaveraged field. The respective time-like, space-like or null character of averaged and unaveraged geodesics is discussed carefully. Finally, some important astrophysical and cosmological applications and consequences are investigated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1140/epjb/e2005-00037-3
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  • 110
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    Strain-induced properties of epitaxial VOx thin films (2005)
    Springer
    The European physical journal 43 (2005), S. 195-200 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. We have grown VOx thin films on different substrates in order to investigate the influence of epitaxial strain on the transport properties. We found that the electric conductivity is much larger for films grown under compressive strain on SrTiO3 substrates, as compared to bulk material and VOx films grown under tensile strain on MgO substrates. A clear crossover from metallic to semiconducting behavior is observed when increasing the oxygen content x. Apparently, the application of strain induces a Mott-Hubbard insulator-to-metal transition in VOx〈1. The VOx/SrTiO3 films show an unexpected large positive magnetoresistance effect at low temperatures, which is not found in the VOx films grown under tensile strain on MgO or on a substrate with a similar lattice parameter.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1140/epjb/e2005-00042-6
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  • 111
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    Theory of neutron scattering for gapless neutral spin-1 collective mode in graphite (2005)
    Springer
    The European physical journal 43 (2005), S. 175-185 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. Using tight binding band picture for 2D graphite, and the Hubbard interaction, recently we obtained a gapless, neutral spin-1 collective mode branch in graphite [Phys. Rev. Lett. 89, 016402]. In this paper we present a detailed RPA analysis of the Neutron Scattering cross section for this collective mode. Near K-point and very close to Γ-point, the intensity of neutron scattering peaks vanishes as q3. This is shown using a simple Dirac cone model for the graphite band structure, which captures the small-q behavior of the system. As we move away from the Γ- and K-points in the Brillouin zone of the collective mode momenta, we can identify our collective mode quanta with spin triplet excitons with the spatial extent of the order of a few to a couple of lattice parameter a, with more or less anisotropic character, which differs from point to point. We also demonstrate that the inclusion of the long range tail of the Coulomb interaction in real graphite, does not affect our spin-1 collective mode qualitatively. This collective mode could be probed at different energy scales by thermal, hot and epithermal neutron scattering experiments. However, the smallness of the calculated scattering intensity, arising from a reduced form factor of carbon 2pz orbital makes the detection challenging.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1140/epjb/e2005-00040-8
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  • 112
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    Magnetic AC susceptibility of stoichiometric and low zinc doped magnetite single crystals (2005)
    Springer
    The European physical journal 43 (2005), S. 201-212 
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    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. Systematic studies of AC susceptibility in a stoichiometric magnetite single crystal, in a series of low zinc doped magnetite (xZn 〈 0.04) and in nonstoichiometric magnetite samples (both single crystals and pellets) in the temperature range 4–300 K are presented. Measurements were performed in several AC fields ( $H_{AC}=0.2{-}20\ $ Oe) and at different frequencies (15–6000 Hz). It is suggested that the signal is primarily due to magnetic domain wall movement, strongly influenced by structural domains (twins). Two sets of anomalies were found: the first is associated with the Verwey transition and the second involves two different effects, one at 28 K, observed only in stoichiometric magnetite, and the other at 50 K. While the temperature position of the first anomaly (28 K) does not depend on frequency, the effect at 50 K is associated with an activation process, shifting to higher temperatures with increasing frequency. This last effect may be linked to the low temperature magnetoelectric effects terminating approximately at those temperatures. Qualitatively similar results have been observed by the Magnetic After Effect technique presented in the literature, that is associated with relaxation times that are 104 higher than those characteristic of our technique.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1140/epjb/e2005-00043-5
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  • 113
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    HSSH-model of Hole transfer in DNA (2005)
    Springer
    The European physical journal 43 (2005), S. 279-281 
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    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. A method based on a selfconsistent solution of a quantum-mechanical system with temperature fluctuations described by Langevin equations is developed to calculate the charge carrier mobility in DNA. To model the charge transfer in DNA, a combined Holstein – SSH Hamiltonian is considered. As an example the hole mobility is calculated at room temperature for synthetic poly (G)/poly (C) duplex with regard to main structural fluctuations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1140/epjb/e2005-00049-y
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  • 114
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    Ripple formation over a sand bed submitted to a laminar shear flow (2005)
    Springer
    The European physical journal 43 (2005), S. 283-294 
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    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. We investigate the process of ripple formation in a viscous fluid when a sand bed is submitted to a laminar shear flow. We propose a new description for the sand transport which takes into account the fact that the transport rate does not adapt instantaneously to a change of the fluid velocity due to grain inertia. It introduces a new length, called here after equilibrium length leq, corresponding to the distance needed for a immobile grain to equilibrate its velocity with that of the fluid. The transport rate is therefore found to depend not only on the fluid shear stress and bed slope (as usually assumed) but also on grain inertia. Within the framework of this model we analyzed the mechanisms of the sand bed instability. It is found that the instability results from the competition between the destabilizing effect of fluid inertia and the stabilizing ones of grain inertia and bed slope. We derive analytical scaling laws for the most amplified wavelength, its growth rate and phase velocity. We found in particular that at small particle Reynolds number Rep, the most amplified wavelength scales as the viscous length lν defined as $\sqrt{\nu/\gamma}$ (where γ is the shear rate and ν the fluid viscosity) and at large Rep it scales as the equilibrium length leq. Our results are compared with available experimental data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1140/epjb/e2005-00050-6
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  • 115
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    Diagram technique for finding of vertex functions in the Landau theory of heteropolymer liquids (2005)
    Springer
    The European physical journal 43 (2005), S. 251-269 
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    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. The problem on finding the coefficients of the Landau free energy expansion into the power series of parameter of order has been considered for solutions and melts of linear heteropolymers whose molecules comprise several types monomeric units arranged stochastically. The presence of such a quenched structural disorder places this problem outside the framework of the traditional statistical physics inviting for its solution special approaches. One of them, based on the replica concept and actively engaged in theoretical physics of disordered systems, has been invoked in this paper to derive expressions for the vertex functions in the Landau theory of heteropolymer liquids. An algorithm has been formulated which permits one resorting to the simple diagram technique to write down expressions for these functions of any order in terms of the statistical characteristics of chemical quenched structure of polymer molecules. Explicit expressions for the contributions to the Landau free energy up to the fourth degree of order parameters for polymer systems with an arbitrary structural disorder have been presented to illustrate this general algorithm. Its potentialities have been also exemplified for the melt of random m-component copolymer where exact analytical formulas for these contributions up to n=6 at an arbitrary m have been derived for the first time.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1140/epjb/e2005-00047-1
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  • 116
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    Uncompensated antiferromagnetic structure of Ho2Ni2Pb (2005)
    Springer
    The European physical journal 43 (2005), S. 163-174 
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    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. We have studied the magnetic structure of the orthorhombic compound Ho2Ni2Pb by means of neutron diffraction in zero field and in magnetic fields up to 4.5 T. Both powder and single-crystalline samples were used. Previous bulk measurements suggest two distinct magnetic phase transitions: one at TN = 7.0 K and the other at 4.8 K. Our neutron diffraction measurements, which were made in the range 1.5-20 K, showed that Ho2Ni2Pb has a collinear magnetic structure with unequal number of up and down Ho moments that are aligned parallel and antiparallel to the c axis. At the lowest temperatures the Ho moments are equal in size, each 8.3 μB in agreement with magnetization data. The magnetic structure can be described as having a 5a ×b ×c magnetic unit cell. Below Ts = 3.0 K the structure is squared up. A smooth development of all the magnetic moment magnitudes indicates that the magnetic structure remains in principle the same over the whole temperature range, the “phase transition” around 4.8 K can be identified as an inflection point in the temperature dependence of one of the Ho moments. With increasing temperature there is a clear development towards a simple transverse sine-wave modulated magnetic structure that is established just below TN.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1140/epjb/e2005-00039-1
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  • 117
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    Moment instabilities in multidimensional systems with noise (2005)
    Springer
    The European physical journal 43 (2005), S. 221-242 
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    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. We present a systematic study of moment evolution in multidimensional stochastic difference systems, focusing on characterizing systems whose low-order moments diverge in the neighborhood of a stable fixed point. We consider systems with a simple, dominant eigenvalue and stationary, white noise. When the noise is small, we obtain general expressions for the approximate asymptotic distribution and moment Lyapunov exponents. In the case of larger noise, the second moment is calculated using a different approach, which gives an exact result for some types of noise. We analyze the dependence of the moments on the system’s dimension, relevant system properties, the form of the noise, and the magnitude of the noise. We determine a critical value for noise strength, as a function of the unperturbed system’s convergence rate, above which the second moment diverges and large fluctuations are likely. Analytical results are validated by numerical simulations. Finally, we present a short discussion of the extension of our results to the continuous time limit.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1140/epjb/e2005-00045-3
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  • 118
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    Frequency clustering of coupled phase oscillators on small-world networks (2005)
    Springer
    The European physical journal 43 (2005), S. 243-250 
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    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. We analyze the phenomenon of frequency clustering in a system of coupled phase oscillators. The oscillators, which in the absence of coupling have uniformly distributed natural frequencies, are coupled through a small-world network, built according to the Watts-Strogatz model. We study the time evolution and determine variations in the transient times depending on the disorder of the network and on the coupling strength. We investigate the effects of fluctuations in the average frequencies, and discuss the definition of the threshold for synchronization. We characterize the structure of clusters and the distribution of cluster sizes in the synchronization transition, and define suitable order parameters to describe the aggregation of the oscillators as the network disorder and the coupling strength change. The non-monotonic behavior observed in some order parameters is related to fluctuations in the mean frequencies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1140/epjb/e2005-00046-2
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  • 119
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    Interaction effects on persistent current of ballistic cylindrical nanostructures (2005)
    Springer
    The European physical journal 43 (2005), S. 405-419 
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    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. We investigate clean cylindrical nanostructures with an applied longitudinal static magnetic field. The ground state of these systems becomes degenerate for particular values of the field due to Aharonov-Bohm effect. The Coulomb interaction introduces couplings between the electronic configurations. Consequently, depending on particular selection rules, the ground state may become, in the interacting case, a many body state at the degeneracy points: a gap is then opened. To study this problem, we propose a variational multireference wave function which goes beyond the Hartree-Fock approximation. Using this ansatz, in addition to the replacements of some crossings by avoided crossings, two other important effects of the electron-electron interaction are pointed out: (i) the long-range part of the Coulomb potential tends to shift the position in magnetic field of the crossing or avoided crossing points and, (ii) at the points of degeneracy or near degeneracy, the interaction can drive the system from a singlet to a triplet state inducing new real crossing points in the ground state energy curve as function of the field. In any case, the crossing points that are due to either orbital or spin effects, should manifest themselves in various experiments as sudden changes in the response of the system (magnetoconductance, magnetopolarisability, ...) when the magnetic field is tuned.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1140/epjb/e2005-00071-1
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  • 120
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    Polaron properties in ternary group-III nitride mixed crystals (2005)
    Springer
    The European physical journal 43 (2005), S. 339-345 
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    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. Polaron properties are studied in bulk wurtzite nitride ternary mixed crystals AxB1-xN (A, B = Al, Ga, In) with the use of a dielectric continuum Fröhlich-like electron-phonon interaction Hamiltonian. The polaronic self-trapping energy and effective mass are analytically derived by taking the mixing properties of the LO and TO polarizations due to the anisotropy effect into account in the mono-phonon approximation. The numerical computation has been performed for the wurtzite ternary mixed crystal materials InxGa1-xN, AlxGa1-xN, and AlxIn1-xN as functions of the composition x. The results show that the polaronic self-trapping energies in the wurtzite structures are bigger than that in zinc-blende structures for the materials calculated. It is also found that the structure anisotropy increases the electron-phonon interaction in wurtizte nitride semiconductors. The results indicate that the LO-like phonon influence on the polaronic self-trapping energy and effective mass is dominant, and the anisotropy effect is obvious.
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    URL: http://dx.doi.org/10.1140/epjb/e2005-00061-3
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  • 121
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    Dimer site-bond percolation on a square lattice (2005)
    Springer
    The European physical journal 43 (2005), S. 363-368 
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    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. A generalization of the pure site and pure bond percolation problems in which pairs of nearest neighbor sites (site dimers) and linear pairs of nearest neighbor bonds (bond dimers) are independently occupied at random on a square lattice is studied. We called this model as dimer site-bond percolation. Motivated by considerations of cluster connectivity, we have used two distinct schemes (denoted as $S\cap B$ and $S\cup B$ ) for dimer site-bond percolation. In $S \cap B$ ( $S \cup B$ ), two points are said to be connected if a sequence of occupied sites and (or) bonds joins them. By using finite-size scaling theory, data from $S \cap B$ and $S \cup B$ are analyzed in order to determine i) the phase boundary between the percolating and non-percolating regions and ii) the numerical values of the critical exponents of the phase transition occurring in the system. The results obtained are discussed in comparison with the corresponding ones for classical monomer site-bond percolation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1140/epjb/e2005-00064-0
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  • 122
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    Ground-state correlations and finite temperature properties of the transverse Ising model (2005)
    Springer
    The European physical journal 43 (2005), S. 373-378 
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    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. We present a semi-analytic study of Ising spins on a simple square or cubic lattice coupled to a transverse magnetic field of variable strength. The formal analysis employs correlated basis functions (CBF) theory to investigate the properties of the corresponding N-body ground and excited states. For these states we discuss two different ansaetze of correlated trial wave functions and associated longitudinal and transverse excitation modes. The formalism is then generalized to describe the spin system at nonzero temperatures with the help of a suitable functional approximating the Helmholtz free energy. To test the quality of the functional in a first step we perform numerical calculations within the extended formalism but ignore spatial correlations. Numerical results are reported on the energies of the longitudinal and the transverse excitation modes at zero temperature, on critical data at finite temperatures, and on the optimized spontaneous magnetization as a function of temperature and external field strength.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1140/epjb/e2005-00066-x
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  • 123
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    Hydrogen desorption from ball milled MgH2 catalyzed with Fe (2005)
    Springer
    The European physical journal 43 (2005), S. 19-27 
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    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. In order to obtain faster hydrogen sorption kinetics, MgH2-Fe nanocomposites were prepared by high-energy ball milling. The MgH2 decomposition was studied in samples obtained by changing in a systematic way both the catalyst amount and the degree of microstructural refinement. To this purpose, blends containing increasing Fe concentration have been ball milled in processing conditions able to impart different amount of structural defects. The resulting samples have been characterized by X-ray diffraction to investigate the microstructural features and the phase composition, while the powder morphology and the degree of catalyst dispersion were analyzed by scanning electron microscopy. Differential scanning calorimetry was carried out to characterize the hydrogen desorption behavior of these nanocomposites. Experimental results clearly show that the characteristics of the desorption process are dominated, among other factors, by the morphology of the catalyst dispersion, which in turns depends on the processing conditions and blend composition. In order to achieve low desorption temperatures the homogeneous catalyst dispersion in micron-size particles throughout the structure is required. This condition can be achieved by suitable tuning of the milling conditions and of the catalyst amount.
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    Generic two-phase coexistence in nonequilibrium systems (2005)
    Springer
    The European physical journal 43 (2005), S. 73-79 
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    ISSN: 1434-6036
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    Topics: Physics
    Notes: Abstract. A beautifully simple model introduced a couple of decades ago, Toom’s cellular automaton, revealed that non-equilibrium systems may exhibit generic bistability, i.e. two-phase coexistence over a finite area of the (two-dimensional) phase diagram, in violation of the equilibrium Gibbs phase rule. In this paper we analyse two interfacial models, describing more realistic situations, that share with Toom’s model a phase diagram with a broad region of phase coexistence. An analysis of the interfacial models yields conditions for generic bistability in terms of physically relevant parameters that may be controlled experimentally.
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    URL: http://dx.doi.org/10.1140/epjb/e2005-00029-3
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    A model reaction diffusion system under spatial perturbation: theoretical and numerical investigation (2005)
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    The European physical journal 43 (2005), S. 109-114 
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    ISSN: 1434-6036
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    Topics: Physics
    Notes: Abstract. We consider a model (Lengyel-Epstein) reaction-diffusion system under spatial parametric modulation and demonstrate the effect of resonance shift of the Hopf-Turing boundary. A systematic perturbative and numerical analysis shows that this shift may induce spatial inhomogeneity on an homogeneous stable state resulting in pattern formation.
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    URL: http://dx.doi.org/10.1140/epjb/e2005-00033-7
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    Decoherence and entanglement in coherent quantum tunneling of magnetization with dissipation (2005)
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    The European physical journal 43 (2005), S. 125-129 
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    ISSN: 1434-6036
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    Notes: Abstract. We study the coherent quantum tunneling of magnetization, for example, in a biaxial molecular magnet with dissipation of the environment which results in the suppression of the tunneling and therefore the decoherence of superposition of macroscopic quantum states in terms of the general spin-boson model. The degree of entanglement between the magnet and the environment is evaluated explicitly with the help of reduced density matrix. We show an interesting relation that the degree of entanglement approaches maximum value when the coherent tunneling is suppressed completely.
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    The effect of iron doping in La0.8Sr0.2Fe0.05Co0.95O3-δ perovskite (2005)
    Springer
    The European physical journal 43 (2005), S. 297-303 
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    ISSN: 1434-6036
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    Topics: Physics
    Notes: Abstract. La0.8Sr0.257Fe0.05Co0.95O3-δ perovskite is investigated by 57Fe transmission and emission Mössbauer spectroscopy, X-ray diffraction, AC magnetic susceptibility and magnetotransport measurements. Temperature dependence of the 57Fe Mössbauer isomer shift, quadrupole splitting, magnetic hyperfine field, line broadening, and relative spectral area is presented in a detailed manner for La0.8Sr0.257Fe0.05Co0.95O3-δ . The oxidation state of iron is determined to be Fe3+, and the presence of preferential electronic charge compensation Fe3+ ↦  Fe4+ over that of Co3+ ↦ Co4+ is excluded. Relaxation of iron magnetic moments reflected by the 57Fe Mössbauer spectra of La0.8Sr0.257Fe0.05Co0.95O3-δ are interpreted as evidence for the existence of superparamagnetic like Co clusters and a corresponding cluster glass magnetic phase formed below T ≈65 K.
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    Electrical and magnetic properties of Gd(Ba2-xLax)Cu3O7+δ (2005)
    Springer
    The European physical journal 43 (2005), S. 305-318 
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    Notes: Abstract. We have studied the structural, electrical, and magnetic properties of the normal and superconducting states Gd(Ba2-xLax)Cu3O7+δ [Gd(BaLa)123] samples with 0.0 ≤x ≤0.8 prepared by the standard solid-state reaction. XRD characterization shows an orthorhombic-tetragonal structural transition at x=0.2. Iodometric titration analysis shows the oxygen content of the samples increase with the increase of La doping. The resistivity curves show that for x≤0.15, there is metallic behavior, and for x≥0.2, there is a gradual insulating transition behavior in the normal state. The metal-insulator and superconductor-insulator transitions occur between x=0.35 and x=0.4. The superconducting transition temperature decreases with the increase of La content as two-step curve. The normal-state resistivity is fitted for two and three dimensional variable range hopping (2D&3D-VRH) and Coulomb gap (CG) regimes, separately. The results show that the dominant mechanism is CG for x≤0.35, and VRH for x≥0.4. The pinning energy U, derived from the thermally activated flux creep (TAFC) model and Ambegaokar-Halperin (AH) theory, shows a power-law relation as U∼H -β. The critical current density decreases with the increase of La doping and magnetic field. The E-J curves show that the induced electric field increases with the increase of magnetic field and La concentration. The magnetization measurements indicate that the critical penetration fields and magnetic current density decrease with La doping.
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    A molecular dynamics investigation of dynamical heterogeneity in supercooled water (2005)
    Springer
    The European physical journal 43 (2005), S. 355-362 
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    Notes: Abstract. We investigate the presence of dynamical heterogeneity in supercooled water with molecular dynamics simulations using the new water model proposed by Mahoney and Jorgensen [M.W. Mahoney, W.L. Jorgensen J. Chem. Phys. 112, 8910 (2000)]. Prompted by recent theoretical results [J.P. Garrahan, D. Chandler, Phys. Rev. Lett. 89, 35704 (2002)] we study the dynamical aggregation of the least and the most mobile molecules. We find dynamical heterogeneity in supercooled water and string-like dynamics for the most mobile molecules. We also find the dynamical aggregation of the least mobile molecules. The two kinds of dynamical aggregation appear however to be very different. Characteristic times are different and evolve differently. String-like motions appear only for the most mobile molecules, a result predicted by the facilitation theory. The aggregation of the least mobile molecules is more organized than the bulk while the opposite is observed for the most mobile molecules.
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    Self organized scale-free networks from merging and regeneration (2005)
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    The European physical journal 43 (2005), S. 369-372 
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    Notes: Abstract. We propose that the ubiquitous scale free nature of many real world networks may emerge from a steady state process where nodes are created and merged randomly. The merging may be viewed as an optimization of efficiency by minimizing redundancy.
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    Spin-polarized transport through a coupled double-dot (2005)
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    The European physical journal 43 (2005), S. 421-427 
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    Notes: Abstract. We investigate the quantum transport through a mesoscopic device consisting of an open, lateral double-quantum-dot coupled by time oscillating and spin-polarization dependent tunneling which results from a static magnetic field applied in the tunneling junction. In the presence of a non-vanishing bias voltage applied to two attached macroscopic leads both spin and charge currents are driven through the device. We demonstrate that the spin and charge currents are controllable by adjusting the gate voltage, the frequency of driving field and the magnitude of the magnetic field as well. An interesting resonance phenomenon is observed.
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    Dimensional reduction of the Abelian Higgs Carroll-Field-Jackiw model (2005)
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    The European physical journal 38 (2005), S. 511-519 
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    Notes: Abstract. Taking as a starting point a Lorentz non-invariant abelian Higgs model defined in 1 + 3 dimensions, we carry out its dimensional reduction to D = 1 + 2, obtaining a new planar model composed by a Maxwell-Chern-Simons-Proca gauge sector, a massive scalar sector, and a mixing term (involving the fixed background $v^{\mu}$ ) that imposes the Lorentz violation to the reduced model. The propagators of the scalar and massive gauge field are evaluated and the corresponding dispersion relations determined. Based on the poles of the propagators, a causality and unitarity analysis is carried out at tree level. We then show that the model is totally causal, stable and unitary.
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    Measurement of the energy dependence of hadronic jet rates and the strong coupling $\alpha_s$ from the four-jet rate with the DELPHI detector at LEP (2005)
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    The European physical journal 38 (2005), S. 413-426 
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    Notes: Abstract. Hadronic events from the data collected with the DELPHI detector at LEP within the energy range from 89 Gev to 209 Gev are selected, their jet rates are determined and compared to predictions of four different event generators. One of them is the recently developed APACIC + + generator which performs a massive matrix element calculation matched to a parton shower followed by string fragmentation. The four-jet rate is used to measure $\alpha_s$ in the next-to-leading-order approximation yielding $${\alpha_s(M_Z^2)} = 0.1175 \pm 0.0030. $$ The running of $\alpha_s$ determined by using four-jet events has been tested. The logarithmic energy slope is measured to be $$ \frac{{\mathrm{d}}\alpha_s^{-1}}{{\mathrm{d}} \log E_{\mathrm {cm}}} = 1.14 \pm 0.36. $$ Since the analysis is based on four-jet final states it represents an alternative approach to previous DELPHI $\alpha_s$ measurements using event shape distributions.
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    Inclusive production of D + , D 0, D s + and D * + mesonsin deep inelastic scattering at HERA (2005)
    Springer
    The European physical journal 38 (2005), S. 447-459 
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    ISSN: 1434-6052
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    Topics: Physics
    Notes: Abstract. Inclusive production cross sections are measured in deep inelastic scattering at HERA for meson states composed of a charm quark and a light antiquark or the charge conjugate. The measurements cover the kinematic region of photon virtuality 2 〈 Q 2 〈 100 Gev2, inelasticity 0.05 〈 y 〈 0.7, D meson transverse momenta $p_t(D) \ge 2.5$ Gev and pseudorapidity $\vert\eta(D)\vert \le 1.5$ . The identification of the D-meson decays and the reduction of the combinatorial background profit from the reconstruction of displaced secondary vertices by means of the H1 silicon vertex detector. The production of charmed mesons containing the light quarks u,d and s is found to be compatible with a description in which the hard scattering is followed by a factorisable and universal hadronisation process.
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    Measurement of prompt photon cross sections in photoproduction at HERA (2005)
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    The European physical journal 38 (2005), S. 437-445 
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    Topics: Physics
    Notes: Abstract. Results are presented on the photoproduction of isolated prompt photons, inclusively and associated with jets, in the $\gamma p$ center of mass energy range 142 〈 W 〈 266 GeV. The cross sections are measured for the transverse momentum range of the photons $5 〈 E_T^{\gamma} 〈 10$ GeV and for associated jets with E T jet 〉 4.5 GeV. They are measured differentially as a function of $E_T^{\gamma}, E_T^{\mathrm{jet}}$ , the pseudorapidities $\eta^{\gamma}$ and $\eta^{\mathrm{jet}}$ and estimators of the momentum fractions $x_{\gamma}$ and x p of the incident photon and proton carried by the constituents participating in the hard process. In order to further investigate the underlying dynamics, the angular correlation between the prompt photon and the jet in the transverse plane is studied. Predictions by perturbative QCD calculations in next to leading order are about $30\%$ below the inclusive prompt photon data after corrections for hadronisation and multiple interactions, but are in reasonable agreement with the results for prompt photons associated with jets. Comparisons with the predictions of the event generators PYTHIA and HERWIG are also presented.
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    Split supersymmetry at colliders (2005)
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    The European physical journal 39 (2005), S. 229-243 
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    Topics: Physics
    Notes: Abstract. We consider the collider phenomenology of split-supersymmetry models. Despite the challenging nature of the signals in these models the long-lived gluino can be discovered with masses above 2 TeV at the LHC. At a future linear collider we will be able to observe the renormalization group effects from split supersymmetry, using measurements of the neutralino and chargino masses and cross sections.
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    Generalized parton distributions from nucleon form factor data (2005)
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    The European physical journal 39 (2005), S. 1-39 
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    Topics: Physics
    Notes: Abstract. We present a simple empirical parameterization of the x- and t-dependence of generalized parton distributions at zero skewness, using forward parton distributions as input. A fit to experimental data for the Dirac, Pauli and axial form factors of the nucleon allows us to discuss quantitatively the interplay between longitudinal and transverse partonic degrees of freedom in the nucleon (“nucleon tomography”). In particular we obtain the transverse distribution of valence quarks at given momentum fraction x. We calculate various moments of the distributions, including the form factors that appear in the handbag approximation to wide-angle Compton scattering. This allows us to estimate the minimal momentum transfer required for reliable predictions in that approach to be around $\vert t\vert \simeq 3 {\rm GeV}^2$ . We also evaluate the valence contributions to the energy-momentum form factors entering Ji’s sum rule.
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    Spin effects in the electron structure functions (2005)
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    The European physical journal 39 (2005), S. 55-59 
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    Notes: Abstract. The electron structure functions are studied in polarized e + e - scattering. The formulae for longitudinally and transversely polarized electrons are presented. The smallness of the electron mass leads to negligible cross-sections and asymmetries in some cases. Positivity constraints on the structure functions and parton densities are constructed and discussed. The cross-section asymmetries at very high energies, where the inclusion of all elecroweak bosons is necessary, are calculated. Numerical examples, using the asymptotic solutions for the parton densities inside the electron, are presented.
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    Two loop $\overline{{\rm MS}}$ gluon pole mass from the LCO formalism (2005)
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    The European physical journal 39 (2005), S. 61-69 
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    Notes: Abstract. We compute the pole mass of the gluon in QCD from the local composite operator formalism at two loops in the $\overline{{\rm MS}}$ renormalization scheme. For the Yang-Mills theory an estimate of the mass at two loops is $2.13\Lambda_{\overline{{\rm MS}}}$ .
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    Renormalization of the neutrino mass operators in the multi-Higgs-doublet standard model (2005)
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    The European physical journal 39 (2005), S. 219-227 
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    Notes: Abstract. We derive the renormalization group equations (RGE) for the flavor coupling matrices of the effective dimension-five operators which yield Majorana neutrino masses in the multi-Higgs-doublet standard model; in particular, we consider the case where two different scalar doublets occur in those operators. We also write down the RGE for the scalar-potential quartic couplings and for the Yukawa couplings of that model, in the absence of quarks. As an application of the RGE, we consider two models which, based on a μ- $\tau$ interchange symmetry, predict maximal atmospheric neutrino mixing, together with U e3 = 0, at the seesaw scale. We estimate the change of those predictions due to the evolution of the coupling matrices of the effective mass operators from the seesaw scale down to the electroweak scale. We derive an upper bound on that change, thereby finding that the radiative corrections to those predictions are in general negligible.
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    T-dependent Dyson-Schwinger equation in IR regime of QCD: the critical point (2005)
    Springer
    The European physical journal 39 (2005), S. 209-218 
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    Topics: Physics
    Notes: Abstract. The quark mass function $\Sigma(p)$ in QCD is revisited, using a gluon propagator in the form 1/(k 2 + m g 2) plus $2\mu^2/ (k^2 + m_g^2)^2$ , where the second (IR) term gives linear confinement for m g = 0 in the instantaneous limit, μ being another scale. To find $\Sigma(p)$ we propose a new (differential) form of the Dyson-Schwinger equation (DSE) for $\Sigma(p)$ , based on an infinitesimal subtractive renormalization via a differential operator which lowers the degree of divergence in integration on the RHS, by two units. This warrants $\Sigma(p-k)\approx \Sigma(p)$ in the integrand since its k-dependence is no longer sensitive to the principal term (p-k)2 in the quark propagator. The simplified DSE (which incorporates the Ward-Takahashi (WT) identity in the Landau gauge) is satisfied for large p 2 by $\Sigma(p)$ = $\Sigma(0)/(1 + \beta p^2)$ , except for Log factors. The limit p 2 = 0 determines $\Sigma_0$ . A third limit, p 2 = -m 0 2, defines the dynamical mass m 0 via $\Sigma({\mathrm {i}} m_0) = + m_0$ . After two checks ( $f_{\pi} = 93\pm 1$ MeV and $ \langle q{\bar{q}}\rangle $ = $(280 \pm 5 {\mathrm {MeV}})^3$ ), for $1.5 〈 \beta 〈 2$ with $\Sigma_0 = 300 $ MeV, the T-dependent DSE is used in the real time formalism to determine the “critical” index $\gamma = 1/3$ analytically, with the IR term partly serving as the H-field. We find $T_{\mathrm {c}} = 180 \pm 20 $ MeV and check the vanishing of $f_{\pi}$ and $ \langle q{\bar{q}}\rangle $ at T c.
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    Nuclear parton distribution functions and energy-loss effect in the Drell-Yan reaction off nuclei (2005)
    Springer
    The European physical journal 39 (2005), S. 179-184 
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    Topics: Physics
    Notes: Abstract. The energy-loss effect in nuclear matter is another nuclear effect apart from the nuclear effects on the parton distribution as in deep inelastic scattering process. The quark energy loss can be measured best by the nuclear dependence of the high energy nuclear Drell-Yan process. By means of two typical kinds of quark energy-loss parametrization and the different sets of nuclear parton distribution functions, we present an analysis of the E866 experiments on the nuclear dependence of Drell-Yan lepton pair production resulting from the bombardment of Be, Fe and W targets by 800 GeV protons at Fermilab. It is found that the quark energy loss in cold nuclei is strongly dependent on the used nuclear parton distribution functions. The further prospects of using relatively low energy protons incident on nuclear targets are presented by combining the quark energy-loss rate determined from a fit to the E866 nuclear-dependent ratios versus x 1, with the nuclear parton distribution functions given from lA deep inelastic scattering (DIS) data. The experimental study of the relatively low energy nuclear Drell-Yan process can give valuable insight in the energy loss of the fast quark propagating through cold nuclei and help to pin down nuclear parton distribution functions.
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    Transverse-momentum-ordered showers and interleaved multiple interactions (2005)
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    The European physical journal 39 (2005), S. 129-154 
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    Notes: Abstract. We propose a sophisticated framework for high-energy hadronic collisions, wherein different QCD physics processes are interleaved in a common sequence of falling transverse-momentum values. Thereby phase-space competition is introduced between multiple parton-parton interactions and initial-state radiation. As a first step we develop new transverse-momentum-ordered showers for initial- and final-state radiation, which should be of use also beyond the scope of the current article. These showers are then applied in the context of multiple interactions, and a few tests of the new model are presented. The article concludes with an outlook on further aspects, such as the possibility of a shower branching giving partons participating in two different interactions.
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    Spectrum of recoil nucleons in quasi-elastic neutrino-nucleus interactions (2005)
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    The European physical journal 39 (2005), S. 195-200 
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    Notes: Abstract. We have analyzed the consequences of introducing the local density approximation combined with an effective nuclear momentum-dependent potential into the CC quasi-elastic neutrino-nucleus scattering. We note that the distribution of recoil nucleons momenta becomes smooth for low momentum values and the sharp threshold is removed. Our results may be relevant for Sci-Fi detector analysis of K2K experiments. The total amount of observed recoil protons is reduced because some of them remain bound inside the nucleus. We compare theoretical predictions for a probability of such events with the results given by NUX + FLUKA MC simulations.
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    Parton distributions incorporating QED contributions (2005)
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    The European physical journal 39 (2005), S. 155-161 
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    Notes: Abstract. We perform a global parton analysis of deep inelastic and related hard-scattering data, including ${{\mathcal{O}}}(\alpha_{\rm QED})$ corrections to the parton evolution. Although the quality of the fit is essentially unchanged, there are two important physical consequences. First, the different DGLAP evolution of u and d type quarks introduces isospin violation, i.e. $u^p \neq d^n$ , which is found to be unambiguously in the direction to reduce the NuTeV $\sin^2\theta_W$ anomaly. A second consequence is the appearance of photon parton distributions $\gamma(x,Q^2)$ of the proton and the neutron. In principle these can be measured at HERA via the deep inelastic scattering processes $e N \to e\gamma X$ ; our predictions are in agreement with the present data.
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    Gauge theories with non-unitary parallel transporters: a soluble Higgs model* (2005)
    Springer
    The European physical journal 39 (2005), S. 483-497 
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    Topics: Physics
    Notes: Abstract. It has been proposed to abandon the requirement that parallel transporters in gauge theories are unitary (or pseudo-orthogonal). This leads to a geometric interpretation of Vierbein fields as parts of gauge fields, and non-unitary parallel transport in extra directions yields Higgs fields. In such theories, the holonomy group H is larger than the gauge group G. Here we study a one-dimensional model with fermions which retains only the extra dimension, and which is soluble in the sense that its renormalization group flow may be exactly computed, with G = SU(2) and non-compact $H\subseteq GL(2,\mathbf{C})$ , or G = U(2), H = GL(2,C). In all cases the asymptotic behavior of the Higgs potential is computed, and with one possible exception for G = SU(2), H = GL(2,C), there is a flow of the action from a UV fixed point which describes a SU(2)-gauge theory with unitary parallel transporters, to a IR fixed point. We explain how exponential mass ratios of fermions of different flavor can arise through spontaneous symmetry breaking, within the general framework.
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    URL: http://dx.doi.org/10.1140/epjc/s2004-02036-7
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    Non-equivalence between Heisenberg XXZ spin chain and Thirring model (2005)
    Springer
    The European physical journal 39 (2005), S. 511-518 
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    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. The Bethe ansatz equations for the spin 1/2 Heisenberg XXZ spin chain are numerically solved, and the energy eigenvalues are determined for the antiferromagnetic case. We examine the relation between the XXZ spin chain and the massless Thirring model, and show that the spectrum of the XXZ spin chain has a gapless excitation while the regularized Thirring model calculated with the Bogoliubov transformation method has a finite gap. This finite gap spectrum is also confirmed by the Bethe ansatz solution of the massless Thirring model.
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    URL: http://dx.doi.org/10.1140/epjc/s2004-02093-x
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    Radiative return at $\Phi$ - and B-factories: FSR for muon pair production at next-to-leading order (2005)
    Springer
    The European physical journal 39 (2005), S. 411-420 
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    Notes: Abstract. Muon pair production through the radiative return is of importance for a measurement of the hadronic production cross section in two ways: it provides an independent calibration and it may give rise to an important background for the measurement of the pion form factor. With this motivation the Monte Carlo event generator PHOKHARA is extended to include next-to-leading order radiative corrections to the reaction $e^ + e^-\to \mu^ + \mu^-\gamma$ . Furthermore, virtual ISR corrections to FSR from pions are introduced, which extends the applicability of the generator into a new kinematical regime. Finally, the effect of photon vacuum polarization is introduced into this new version of the generator.
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    URL: http://dx.doi.org/10.1140/epjc/s2004-02103-1
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    A search for the fourth SM family quarks at the Tevatron (2005)
    Springer
    The European physical journal 39 (2005), S. 499-501 
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    Topics: Physics
    Notes: Abstract. It is shown that the fourth standard model (SM) family quarks can be observed at the Fermilab Tevatron if their anomalous interactions with known quarks have sufficient strength.
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    URL: http://dx.doi.org/10.1140/epjc/s2004-02110-2
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    High-precision predictions for the MSSM Higgs sector at ${{\mathcal{O}}}(\alpha_b\alpha_s)$ (2005)
    Springer
    The European physical journal 39 (2005), S. 465-481 
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    Topics: Physics
    Notes: Abstract. We evaluate $\mathcal{O}{\alpha_b \alpha_s}$ corrections in the Higgs boson sector of the $\mathcal{C}P$ -conserving MSSM, generalising the known result in the literature to arbitrary values of $\tan\beta$ . A detailed analysis of the renormalisation in the bottom/scalar bottom sector is performed. Concerning the lightest MSSM Higgs boson mass, we find relatively small corrections for positive μ, while for $\mu 〈 0$ the genuine two-loop $\mathcal{O}{\alpha_b \alpha_s}$ corrections can amount up to 3 GeV. Different renormalisation schemes are applied and numerically compared. It is demonstrated that some care has to be taken in choosing an appropriate renormalisation prescription in order to avoid artificially large corrections. The residual dependence on the renormalisation scale is investigated, and the remaining theoretical uncertainties from unknown higher-order corrections in this sector are discussed for different regions of the MSSM parameter space.
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    URL: http://dx.doi.org/10.1140/epjc/s2005-02112-6
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    Complete description of polarization effects in e + e - pair productionby a photon in the field of a strong laser wave (2005)
    Springer
    The European physical journal 40 (2005), S. 27-40 
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    Topics: Physics
    Notes: Abstract. We consider production of a e + e - pair by a high-energy photon in the field of a strong laser wave. A probability of this process for circularly or linearly polarized laser photons and for arbitrary polarization of all other particles is calculated. We obtain the complete set of functions which describe such a probability in a compact invariant form. Besides, we discuss in some detail the polarization effects in the kinematics relevant to the problem of $e\to \gamma$ conversion at $\gamma \gamma$ and ${\gamma e}$ colliders.
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    URL: http://dx.doi.org/10.1140/epjc/s2005-02125-1
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    The role of strange sea quarks in chiral extrapolations on the lattice (2005)
    Springer
    The European physical journal 40 (2005), S. 81-96 
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    Notes: Abstract. Since the strange quark has a light mass of order $O(\Lambda_{\mathrm {{QCD}}})$ , fluctuations of sea $s\bar{s}$ pairs may play a special role in the low-energy dynamics of QCD by inducing significantly different patterns of chiral symmetry breaking in the chiral limits N f = 2 (m u = m d = 0, m s physical) and N f = 3 (m u = m d = m s = 0). This effect of vacuum fluctuations of $s\bar{s}$ pairs is related to the violation of the Zweig rule in the scalar sector, described through the two O(p 4) low-energy constants L 4 and L 6 of the three-flavour strong chiral lagrangian. In the case of significant vacuum fluctuations, three-flavour chiral expansions might exhibit numerical competition between leading- and next-to-leading-order terms according to the chiral counting, and chiral extrapolations should be handled with special care. We investigate the impact of the fluctuations of $s\bar{s}$ pairs on chiral extrapolations in the case of lattice simulations with three dynamical flavours in the isospin limit. Information on the size of the vacuum fluctuations can be obtained from the dependence of the masses and decay constants of pions and kaons on the light quark masses. Even in the case of large fluctuations, corrections due to the finite size of spatial dimensions can be kept under control for large enough boxes ( $L\sim 2.5$ fm).
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    URL: http://dx.doi.org/10.1140/epjc/s2005-02130-4
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    Factorisation, parton entanglement and the Drell-Yan process (2005)
    Springer
    The European physical journal 40 (2005), S. 55-61 
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    Topics: Physics
    Notes: Abstract. We discuss the angular distribution of the lepton pair in the Drell-Yan process, $\text{hadron} + \text{hadron}\to\gamma^* + X\to l^ + + l^- + X$ . This process gives information on the spin-density matrix $\rho^{(q,\bar{q})}$ of the annihilating quark-antiquark pair in $q + \bar{q}\to l^ + + l^-$ . There is strong experimental evidence that even for unpolarised initial hadrons $\rho^{(q,\bar{q})}$ is non-trivial, and therefore the quark-antiquark system is polarised. We discuss the possibilities of a general $\rho^{(q,\bar{q})}$ - which could be entangled - and a factorising $\rho^{(q,\bar{q})}$ . We argue that instantons may lead to a non-trivial $\rho^{(q,\bar{q})}$ of the type indicated by experiments.
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    Collins effect in single spin asymmetries of the $p^{\uparrow}p \to \pi X$ process (2005)
    Springer
    The European physical journal 40 (2005), S. 63-67 
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    Notes: Abstract. We investigate the Collins effect in single spin asymmetries (SSAs) of the $p^{\uparrow}p \to \pi X$ process by taking into account the transverse momentum dependence of the microscopic sub-process cross sections, with the transverse momentum in the Collins function integrated over. We find that the asymmetries due to the Collins effect can only explain the available data at best qualitatively, by using our choices of quark distributions in the quark-diquark model and a pQCD-based analysis, together with several options of the Collins function. Our results indicate the necessity to take into account contributions from other effects such as the Sivers effect or twist-3 contributions.
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    Analyses of k t distributions at RHIC by means of some selected statistical and stochastic models (2005)
    Springer
    The European physical journal 40 (2005), S. 243-250 
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    Notes: Abstract. The new data on k t distributions obtained at RHIC are analyzed by means of selected models of statistical and stochastic origin in order to estimate their importance in providing new information on the hadronization process, in particular on the value of the temperature at freeze-out to the hadronic phase.
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    $ B \to D^{(*)}$ transitions in a quark model (2005)
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    The European physical journal 40 (2005), S. 193-197 
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    Notes: Abstract. We propose a constituent quark model to evaluate heavy decay constants and form factors relevant for $ B \to D^{(*)}$ semileptonic transitions. We show that the model reproduces the scaling laws dictated by the spin-flavor symmetry in the heavy quark limit and describes quite well the experimental data.
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    URL: http://dx.doi.org/10.1140/epjc/s2005-02143-y
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    Infrared regularization for spin-1 fields (2005)
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    The European physical journal 40 (2005), S. 97-119 
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    Notes: Abstract. We extend the method of infrared regularization to spin-1 fields. As applications, we discuss the chiral extrapolation of the rho meson mass from lattice QCD data and the pion-rho sigma term.
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    URL: http://dx.doi.org/10.1140/epjc/s2005-02118-0
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    The polarization tensor of neutral gluons in external fields at high temperature (2005)
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    The European physical journal 40 (2005), S. 121-127 
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    Notes: Abstract. The one-loop polarization operator of neutral gluons in the background constant Abelian isotopic, H 3, and hypercharge, H 8, chromomagnetic fields combined with A 0 electrostatic potential at high temperature is calculated. The case when A 0 = 0 is investigated separately. The proper time method is applied. It is found that neutral gluons do not acquire magnetic masses in the background fields, in contrast to the charged ones. The application of the results are discussed.
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    Two-parton twist-3 factorization in perturbative QCD (2005)
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    The European physical journal 40 (2005), S. 395-417 
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    Notes: Abstract. We prove the collinear factorization theorem for the process $\pi\gamma^*\to\pi$ at the twist-3 level in the covariant gauge by means of the Ward identity, concentrating on the two-parton case. It is shown that soft divergences cancel and collinear divergences are grouped into the pseudo-scalar and pseudo-tensor two-parton twist-3 pion distribution amplitudes. The delicate summation of a complete set of diagrams for achieving factorization in momentum, spin, and color spaces is emphasized. The proof is then extended to the exclusive semileptonic decay $B\to\pi l\nu$ , assuming the hard scale to be of $O\smash{\bigl(\sqrt{\bar{\Lambda} M_B}\bigr)}$ , where $\bar{\Lambda}$ is a hadronic scale and M B the B meson mass. We explain the distinction between the factorization of collinear divergences for a pion distribution amplitude and of soft divergences for a B meson distribution amplitude. The gauge invariance and universality of the two-parton twist-3 pion distribution amplitudes are confirmed. The proof presented here can accommodate the leading twist-2 case. We then compare our proof with that performed in the framework of soft-collinear effective theory.
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    URL: http://dx.doi.org/10.1140/epjc/s2005-02147-7
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    Measurement of event shape distributions and moments in e + e $^-\rightarrow \mathrm{hadrons}$ at 91-209 GeV and a determination of $\ensuremath{\alpha_{\mathrm{s}}}$ (2005)
    Springer
    The European physical journal 40 (2005), S. 287-316 
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    Notes: Abstract. We have studied hadronic events from e + e- annihilation data at centre-of-mass energies from 91 to 209 GeV. We present distributions of event shape observables and their moments at each energy and compare with QCD Monte Carlo models. From the event shape distributions we extract the strong coupling $\ensuremath{\alpha_{\mathrm{s}}}$ and test its evolution with energy scale. The results are consistent with the running of $\ensuremath{\alpha_{\mathrm{s}}}$ expected from QCD. Combining all data, the value of $\ensuremath{\alpha_{\mathrm{s}}} \ensuremath{(M_{\mathrm{Z}})}$ is determined to be $$ \ensuremath{\alpha_{\mathrm{s}}}\ensuremath{M_{\mathrm{Z}}} = 0.1191 \pm0.0005 \mathrm{(stat.)} \pm0.0010\mathrm{(expt.)} \pm0.0011 \mathrm{(hadr.)} \pm0.0044 \mathrm{(theo.)}\,. $$ The energy evolution of the moments is also used to determine a value of $\ensuremath{\alpha_{\mathrm{s}}}$ with slightly larger errors: $\ensuremath{\alpha_{\mathrm{s}}} \ensuremath{M_{\mathrm{Z}}}=0.1223\pm 0.0005(\mathrm{stat.})\pm 0.0014(\mathrm{expt.})\pm 0.0016(\mathrm{hadr.})^{+0.0054}_{-0.0036}(\mathrm{theo.})$ .
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    URL: http://dx.doi.org/10.1140/epjc/s2005-02120-6
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    Sneutrino production at e + e - linear colliders: addendum to slepton production (2005)
    Springer
    The European physical journal 40 (2005), S. 435-445 
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    Notes: Abstract. Complementing the preceding study of charged scalar leptons, the sector of the neutral scalar leptons, sneutrinos, is investigated in a high-precision analysis for future e + e - linear colliders. The theoretical predictions for the cross-sections are calculated at the thresholds for non-zero widths and in the continuum including higher-order corrections at the one-loop level. Methods for measuring the sneutrino masses and the electron-sneutrino-gaugino Yukawa couplings are presented, addressing theoretical problems specific for the sneutrino channels.
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    Yukawa coupling structure in intersecting D-brane models (2005)
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    The European physical journal 40 (2005), S. 579-587 
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    Notes: Abstract. The structure of Yukawa coupling matrices is investigated in type IIA T 6/(Z2 x Z2) orientifold models with intersecting D-branes. Yukawa coupling matrices are difficult to be made realistic in conventional models in which the generation structure emerges by the multiple intersection of D-branes in the factorized T 6 = T 2 x T 2 x T 2. We study the new type of flavor structure, where Yukawa couplings are dynamically generated, and show this type of models lead to non-trivial structures of Yukawa coupling matrices, which can be realistic.
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    URL: http://dx.doi.org/10.1140/epjc/s2005-02166-4
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    QCD analysis of dijet production at low Q 2 at HERA (2005)
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    The European physical journal 40 (2005), S. 469-472 
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    Notes: Abstract. Recent H1 data on triple differential dijet cross sections in $e^\pm p$ interactions in the region of low photon virtualities are shown to be in reasonable agreement with the predictions of the NLO QCD calculations obtained using the program NLOJET + + . The implications of this observation for the phenomenological relevance of the concept of resolved virtual photon are discussed.
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    URL: http://dx.doi.org/10.1140/epjc/s2005-02172-6
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    New method to extract the neutron-electron scattering length (2005)
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    The European physical journal 40 (2005), S. 473-477 
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    Notes: Abstract. A novel method to extract the neutron-electron scattering length b ne from the precise neutron scattering data measured for a noble gas at several different densities n is proposed. The main point of this method is dividing the experimental data into two parts: the first, nearly proportional to n, corresponding to diffraction on neighboring atoms and the second one, a small contribution of n, e scattering independent on n. The proposed technique is demonstrated using the structure factor S(q) for gaseous krypton.
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    Final results from phase II of the Mainz neutrino mass searchin tritium ${\beta}$ decay (2005)
    Springer
    The European physical journal 40 (2005), S. 447-468 
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    Notes: Abstract. This paper reports on the improved Mainz experiment on tritium $\beta$ spectroscopy which yields a 10 times higher signal to background ratio than before. The main experimental effects and systematic uncertainties have been investigated in side experiments, and possible error sources have been eliminated. Extensive data taking took place in the years 1997 to 2001. A residual analysis of the data sets yields for the square of the electron antineutrino mass the final result of $m^2(\nu_e) = (-0.6 \pm 2.2_{\mathrm{{stat}}} \pm 2.1_{\mathrm{{syst}}})$ eV2/c4. We derive an upper limit of $m(\nu_e)\leq 2.3$ eV/c2 at 95% confidence level for the mass itself.
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    Fermion kinetics in the Falicov-Kimball limit of the three-band Emery model (2005)
    Springer
    The European physical journal 43 (2005), S. 319-331 
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    Notes: Abstract. The three-band Emery model is reduced to a single-particle quantum model of Falicov-Kimball type, by allowing only up-spins to hop, and forbidding double occupation by projection. It is used to study the effects of geometric obstruction on mobile fermions in thermodynamic equilibrium. For low hopping overlap, there appears a plateau in the entropy, due to charge correlations, and related to real-space disorder. For large overlap, the equilibrium thermopower susceptibility remains anomalous, with a sign opposite to the one predicted from the single-particle density of states. The heat capacity and non-Fermi liquid response are discussed in the context of similar results in the literature. All results are obtained by evaluation of an effective single-particle free-energy operator in closed form. The method to obtain this operator is described in detail.
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    Quantum interference in nanotube electron waveguides (2005)
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    The European physical journal 43 (2005), S. 399-403 
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    Notes: Abstract. We have calculated the quantum conductance of single-walled carbon nanotube (SWNT) waveguide by using a tight binding-based Green’s function approach. Our calculations show that the slow conductance oscillations as well as the fast conductance oscillations are manifestations of the intrinsic quantum interference properties of the conducting SWNTs, being independent of the defect and disorder of the SWNTs. And zigzag type tubes do not show the slow oscillations. The SWNT electron waveguide is also found to have distinctly different transport behavior depending on whether or not the length of the tube is commensurate with a (3N+1) rule, with N the number of basic carbon repeat units along the nanotube length.
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    The investigation of the magnetodielectric effect in multiferroic ferroelectromagnets (2005)
    Springer
    The European physical journal 43 (2005), S. 333-338 
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    Topics: Physics
    Notes: Abstract. In multiferroic ferroelectromagnets, microscopic coupling interaction between the ferroelectric and magnetic order results in the macroscopic correlation between the dielectric and magnetic properties, which is defined as magnetodielectric effect. If we classify multiferroic ferroelectromagnets as two kinds: ferroelectric-ferromagnets and ferroelectric-antiferromagnets, we find the magnetodielectric behavior of these two kinds of ferroeletromagnets show obvious difference. We analyze the origin of the different magnetodielectric behavior and find that the fluctuation of the spin-pair correlation plays a critical role. Soft-mode theory based on DIFFOUR model and the mean-field theory are combined to deal with multiferroic ferroelectromagnetic system.
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    The H+ related defects involved in domain reversal for both near-stoichiometric and heavily Mg-doped lithium niobate crystals (2005)
    Springer
    The European physical journal 43 (2005), S. 347-353 
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    Notes: Abstract. Domain reversal was performed on both near-stoichiometric and heavily Mg-doped lithium niobate crystals. H+ related defect structures in these two types of crystals were studied through the infrared absorption spectra. It is found that the intensity of some decomposed peaks of absorption band change apparently during domain reversal for near-stoichiometric lithium niobate crystals but not for heavily Mg-doped lithium niobate crystals. According to these experimental results, distinct models about H+ related defect structure in LiNbO3 lattice were supposed for them. Nb4+Li and Mg3-Nb were considered as the centers of H+ related defect complex for near-stoichiometric and heavily Mg-doped lithium niobate crystals respectively. Different behavior of them was used to explain the difference of infrared absorption spectra during domain reversal between two types of crystals.
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    Integrable spin-boson interaction in the Tavis-Cummings model from a generic boundary twist (2005)
    Springer
    The European physical journal 43 (2005), S. 387-391 
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    Notes: Abstract. We construct models describing interaction between a spin s and a single bosonic mode using a quantum inverse scattering procedure. The boundary conditions are generically twisted by generic matrices with both diagonal and off-diagonal entries. The exact solution is obtained by mapping the transfer matrix of the spin-boson system to an auxiliary problem of a spin-j coupled to the spin-s with general twist of the boundary condition. The corresponding auxiliary transfer matrix is diagonalized by a variation of the method of Q-matrices of Baxter. The exact solution of our problem is obtained applying certain large-j limit to su(2)j, transforming it into the bosonic algebra.
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    Acoustic radiation force due to incident plane-progressive waves on coated spheres immersed in ideal fluids (2005)
    Springer
    The European physical journal 43 (2005), S. 379-386 
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    Topics: Physics
    Notes: Abstract. In this study, the acoustic radiation force resulting from the interaction of a plane progressive wave with a coated sphere was examined. The linear acoustic scattering problem was obtained first by solving the classical boundary conditions to obtain the required coefficients. The radiation force was then determined by averaging the momentum flux tensor expressed in terms of the total scattering pressure or velocity potential in an ideal fluid. Numerical calculations of the radiation force function Yp , which is the radiation force per unit energy density and unit cross-section, were displayed versus the dimensionless size parameter x=k1 b (k1 is the wave number in the exterior fluid and b the radius of the uncoated sphere) over a large range of frequencies. Particular emphasis has been focused on the coating thickness and the absorption of sound inside the outer covering layer. The fluid-loading effect on the radiation force function curves was also analysed.
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    Rayleigh-Schrödinger-Goldstone variational perturbation theory for many Fermion systems (2005)
    Springer
    The European physical journal 43 (2005), S. 393-398 
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    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. We present a Rayleigh-Schrödinger-Goldstone perturbation formalism for many Fermion systems. Based on this formalism, variational perturbation scheme which goes beyond the Gaussian approximation is developed. In order to go beyond the Gaussian approximation, we identify a parent Hamiltonian which has an effective Gaussian vacuum as a variational solution and carry out further perturbation with respect to the renormalized interaction using Goldstone’s expansion. Perturbation rules for the ground state wavefunctional and energy are found, thus, opening a way for general use of the Schrödinger picture method for many Fermion systems. Useful commuting relations between operators and the Gaussian wavefunctional are also found, which could reduce the calculational efforts substantially. As examples, we calculate the first order correction to the Gaussian wavefunctional and the second order correction to the ground state of an electron gas system with the Yukawa-type interaction.
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    Optoelectronic properties of zinc blende ZnSSe and ZnBeTe alloys (2005)
    Springer
    The European physical journal 43 (2005), S. 3-9 
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    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. The compositional dependence of the electronic band structure has been computed for zinc blende ZnSxSe1-x and Zn1-xBexTe alloys with composition x ranging from 0 to 1. The empirical pseudo potential method with the virtual crystal approximation have been used. A particlar attention has been paid to the effect of alloy disorder on the electronic properties of the II-VI studied compounds. For this purpose, the compositional disorder is added to the virtual crystal approximation as an effective potential. Such correction approximates significantly our calculated values of the band gap bowing parameters to experimental ones. The ZnSxSe1-x gap energy shows a nonlinear behavior with strong bowing for low compositions of sulfur. The Zn1-xBexTe compound, as it is known, can be direct or indirect semiconductor depending on its beryllium composition x. The electron effective mass and the refractive index have been investigated as well. Polynomial approximations are obtained for both the energy gap and the effective mass as functions of alloy composition at Γ and X valleys.
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    Melting and evaporation transitions in small Al clusters: canonical Monte-Carlo simulations (2005)
    Springer
    The European physical journal 43 (2005), S. 47-52 
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    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. A dimer of bound atoms cannot melt, only dissociate. Bulk metals show a well defined first order transition between their solid and liquid phases. The appearance of the melting transition is explored for increasing clusters sizes via the signatures in the specific heat and the root mean square of the bond lengths δB (Berry parameter) by means of Monte-Carlo simulations of Al clusters modelled by Gupta potentials. Clear signatures of a melting transition appear for N∼6 atoms. Closed-shell effects are shown for clusters with up to 56 atoms. The melting transition is compared in detail with the dissociation transition, which induces a second and possibly much larger local maximum in the specific heat at higher temperatures. Larger clusters are shown to fragment into dimers and trimers, which in turn dissociate at higher temperatures.
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    Lattice vibrational analysis of polyacene (2005)
    Springer
    The European physical journal 43 (2005), S. 53-64 
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    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. Within an extended Su-Schrieffer-Heeger model, we made a lattice vibrational analysis of polyacene. In a singly-charged polyacene, the ground state contains an interchain-coupled polaron of quasi-D2h symmetry, around which we found thirteen localized modes in total. Among these localized modes, five (three B2u and two B3u) are infrared active, six (four Ag and two B1g) modes are Raman active, and the other two localized modes are asymmetric, which are both infrared active and Raman active. For the case a charged polaron is coupled with a neutral soliton in a finite polyacene chain, the vibrational modes are also calculated to display the coupling effect between self-trapping excitations on phonons. It is found that the localized phonons are determined mainly by the charged polaron, but the number and frequencies of the localized modes are influenced by the existence of the neutral soliton.
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    Disturbing synchronization: Propagation of perturbations in networks of coupled oscillators (2005)
    Springer
    The European physical journal 43 (2005), S. 97-108 
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    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. We study the response of an ensemble of synchronized phase oscillators to an external harmonic perturbation applied to one of the oscillators. Our main goal is to relate the propagation of the perturbation signal to the structure of the interaction network underlying the ensemble. The overall response of the system is resonant, exhibiting a maximum when the perturbation frequency coincides with the natural frequency of the phase oscillators. The individual response, on the other hand, can strongly depend on the distance to the place where the perturbation is applied. For small distances on a random network, the system behaves as a linear dissipative medium: the perturbation propagates at constant speed, while its amplitude decreases exponentially with the distance. For larger distances, the response saturates to an almost constant level. These different regimes can be analytically explained in terms of the length distribution of the paths that propagate the perturbation signal. We study the extension of these results to other interaction patterns, and show that essentially the same phenomena are observed in networks of chaotic oscillators.
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    Fractal geometry of critical Potts clusters (2005)
    Springer
    The European physical journal 43 (2005), S. 155-155 
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    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
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    A density functional study of molecular oxygen adsorption and reaction barrier on Pu (100) surface (2005)
    Springer
    The European physical journal 43 (2005), S. 131-141 
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    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. Oxygen molecule adsorptions on a Pu(100) surface have been studied in detail, using the generalized gradient approximation to density functional theory. Dissociative adsorption with a layer by layer alternate spin arrangement of the plutonium layer is found to be energetically more favorable compared to molecular adsorption. Hor2 approach on a bridge site without spin polarization was found to the highest chemisorbed site with an energy of 8.787 eV among all the cases studied. The second highest chemisorption energy of 8.236 eV, is the spin-polarized Hor2 or Ver approach at center site. Inclusion of spin polarization affects the chemisorption processes significantly, non-spin-polarized chemisorption energies being typically higher than the spin-polarized energies. We also find that the 5f electrons to be more localized in spin-polarized cases compared to the non-spin-polarized counterparts. The ionic part of O-Pu bonding plays a significant role, while the Pu 5f-O 2p hybridization was found to be rather week. Also, adsorptions of oxygen push the top of 5f band deeper away from the Fermi level, indicating further bonding by the 5f orbitals might be less probable. Except for the interstitial sites, the work functions increase due to adsorptions of oxygen.
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    On voltage-current characteristics and critical current in Bi-2212 (2005)
    Springer
    The European physical journal 43 (2005), S. 39-45 
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    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. V(I) characteristics have been performed in a monocrystalline microbridge of Bi[ Pb $]-2212$ . The vortex phase diagram has been greatly investigated. Linear but non-ohmic Voltage (Current) (V(I)) curves with a well defined critical current have been observed. A departure from this behavior is observed near the peak effect where an out of equilibrium high threshold current can be stabilized. At high temperature, the critical current persists in the “liquid” state despite the dissipation at the lowest bias. Some implications of these results are discussed. In particular, it is proposed that the surface disorder, rather than the bulk disorder, is responsible for the vortex pinning in this sample.
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    Neutron and light-charged-particle productions in proton-induced reactions on 208Pb at 62.9 MeV (2005)
    Springer
    The European physical journal 23 (2005), S. 49-60 
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    ISSN: 1434-601X
    Keywords: 27.80.+w 190 ⩽ A ⩽ 219 ; 25.40.-h Nucleon-induced reactions ; 25.40.Sc Spallation reactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. Neutrons and light charged particles produced in 62.9MeV proton-induced reactions on 208Pb were measured during a single experiment performed at the CYCLONE facility in Louvain-la-Neuve (Belgium). Two independent experimental set-ups were used to extract double differential cross-sections for neutrons, protons, deuterons, tritons, 3He and alpha-particles. Charged particles were detected using a set of Si- Si- CsI telescopes from 25° to 155°, by step of 10 degrees. Neutrons were measured using shielded DeMoN counters, liquid NE213 scintillators, at 24°, 35°, 55°, 80° and 120°. These data allowed the determination of angle differential, energy differential and total production cross-sections. A comparison with theoretical calculations (MCNPX, FLUKA and TALYS) has been performed. It shows that the neutron and proton production rates are well predicted by MCNPX, using the INCL4 option. All the other codes underestimate the neutron production whereas they overestimate the proton one. For composite particles, which represent 17% of the charged particle total reaction cross-section, neither the shape nor the amplitude of the cross-sections are correctly predicted by the models.
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    Levels in 127La fed by the 127Ce beta-decay (2005)
    Springer
    The European physical journal 23 (2005), S. 33-39 
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    ISSN: 1434-601X
    Keywords: 23.20.Lv γ transitions and level energies ; 27.60.+j 90 ⩽ A ⩽ 149
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. The low-lying levels in 127La have been studied through the β-decay of 127Ce ( T1/2 = 29s) produced by bombarding a natMo target with a 185-MeV 35Cl beam. Reaction products were on-line mass-separated, and γ-ray singles and γ-γ coincidence measurements were performed. Conversion electrons were also measured and multipolarities of transitions have been derived. The half-life of the 210.9-keV level was determined to be (1.9±0.3)ns by the β-γ delayed coincidence technique. The level scheme obtained has been compared with calculations based on the Nilsson model.
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    Measurement of the πmeson polarizabilities via the γp → γπ+n reaction (2005)
    Springer
    The European physical journal 23 (2005), S. 113-127 
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    ISSN: 1434-601X
    Keywords: 12.38.Qk Experimental tests ; 13.40.-f Electromagnetic processes and properties ; 13.60.Le Meson production
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. An experiment on the radiative π{+}-meson photoproduction from the proton ( γp → γπ{+}n) was carried out at the Mainz Microtron MAMI in the kinematic region 537MeV 〈 Eγ 〈 817MeV, 140°≤ $ \theta_{{\gamma \gamma ^{\prime }}}^{{{{\rm cm}}}}$ ≤180°. The π{+}-meson polarizabilities have been determined from a comparison of the data with the predictions of two different theoretical models, the first one being based on an effective pole model with pseudoscalar coupling while the second one is based on diagrams describing both resonant and nonresonant contributions. The validity of the models has been verified by comparing the predictions with the present experimental data in the kinematic region where the pion polarizability contribution is negligible ( s1 〈 5mπ2) and where the difference between the predictions of the two models does not exceed 3%. In the region, where the pion polarizability contribution is substantial ( 5 〈 s1/mπ2 〈 15, -12 〈 t/mπ2 〈 - 2), the difference $\ensuremath{(\alpha -\beta )_{\pi^{+}}}$ of the electric (α) and the magnetic (β) polarizabilities has been determined. As a result we find $\ensuremath{(\alpha -\beta )_{\pi^{+}}=(11.6\pm 1.5_{{\rm stat}}\pm 3.0_{{\rm syst}}\pm 0.5_{{\rm mod}})\times 10^{-4}{}{\rm fm^{3}}}$ . This result is at variance with recent calculations in the framework of chiral perturbation theory.
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    Halo or skin in the excited states of some light mirror nuclei (2005)
    Springer
    The European physical journal 23 (2005), S. 11-17 
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    ISSN: 1434-601X
    Keywords: 21.10.Gv Mass and neutron distributions ; 21.60.Jz Hartree-Fock and random-phase approximations ; 21.10.Dr Binding energies and masses ; 27.20.+n 6 ⩽ A ⩽ 19
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. The properties of three pairs of mirror nuclei 13N- 13C, 15N- 15O and 21Na- 21Ne (these mirror nuclei are all made of a good inert core plus an unpaired valence nucleon) are investigated by using the nonlinear relativistic mean-field (RMF) theory. It is found that the calculated binding energies with two different parameter sets are very close to the experimental ones for both the ground states and the excited states except for the large deformed nuclei. The calculations show that the 2s1/2 excited states of 15N and of 21Na are both weakly bound with a proton halo and a proton skin (or a pigmy proton skin), respectively. In addition, the 1d5/2 excited state of 13C and the 2s1/2 excited state of 15O are also weakly bound with a neutron skin, respectively. The ratio of the valence nucleon radius to matter radius is deduced and it can be regarded as an additional criterion for the existence of exotic structure. The unbound 2s1/2 and 1d5/2 excited states of 13N are also discussed.
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    Search for spontaneous transition of nuclei to a superdense state (2005)
    Springer
    The European physical journal 23 (2005), S. 7-10 
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    ISSN: 1434-601X
    Keywords: 21.10.Ft Charge distribution ; 21.10.-k Properties of nuclei; nuclear energy levels ; 21.65.+f Nuclear matter ; 29.40.Mc Scintillation detectors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. We report the results of an experimental search for spontaneous transition of nuclei from ordinary to superdense state in NaI(Tl). New limits on the superdense-state parameters are presented.
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    General survey of polarization observables in deuteron electrodisintegration (2005)
    Springer
    The European physical journal 23 (2005), S. 147-190 
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    ISSN: 1434-601X
    Keywords: 21.45.+v Few-body systems ; 24.70.+s Polarization phenomena in reactions ; 25.30.Fj Inelastic electron scattering to continuum ; 13.40.-f Electromagnetic processes and properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. Polarization observables in inclusive and exclusive electrodisintegration of the deuteron using a polarized beam and an oriented target are systematically surveyed using the standard nonrelativistic framework of nuclear theory but with leading-order relativistic contributions included. The structure functions and the asymmetries corresponding to the various nucleon polarization components are studied in a variety of kinematic regions with respect to their sensitivity to realistic NN-potential models, to subnuclear degrees of freedom in terms of meson exchange currents, isobar configurations and to relativistic effects in different kinematical regions, serving as a benchmark for a test of present standard nuclear theory with effective degrees of freedom.
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    Coexisting oblate and strongly triaxial structures in 191Pt (2005)
    Springer
    The European physical journal 23 (2005), S. 69-78 
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    ISSN: 1434-601X
    Keywords: 29.30.Kv X- and γ-ray spectroscopy ; 23.20.Lv γ transitions and level energies ; 21.60.Ev Collective models ; 27.80.+w 190 ⩽ A ⩽ 219
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. Excited states in 191Pt have been populated using the reaction 186W + 11B at 85MeV beam energy. Gamma-ray coincidences were measured using the EUROGAM-II spectrometer array. The level scheme has been extended considerably. Evidence for favoured structures of highly triaxial shape with γ ∼ -90° coexisting with oblate structures has been obtained by comparison with total Routhian surface and cranked shell model calculations. The presence of proton excitations in both positive- and negative-parity states has been confirmed.
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    From solar proton burning to pionic deuterium through the Nambu-Jona-Lasinio model of light nuclei (2005)
    Springer
    The European physical journal 23 (2005), S. 1-6 
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    ISSN: 1434-601X
    Keywords: 11.10.Ef Lagrangian and Hamiltonian approach ; 13.75.Gx Pion-baryon interactions ; 36.10.-k Exotic atoms and molecules (containing mesons, muons, and other unusual particles) ; 26.65.+t Solar neutrinos
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. Within the Nuclear Nambu-Jona-Lasinio model of light nuclei (the NNJL model), describing strong low-energy nuclear interactions, we compute the width of the energy level of the ground state of pionic deuterium. The theoretical value fits well the experimental data. Using the cross-sections for the reactions νe + d → p + p + e- and νe + d → p + n + νe, computed in the NNJL model, and the experimental values of the events of these reactions, detected by the SNO Collaboration, we compute the boron neutrino fluxes. The theoretical values agree well with the experimental data and the theoretical predictions within the Standard Solar Model by Bahcall. We argue the applicability of the constraints on the astrophysical factor for the solar proton burning, imposed by helioseismology, to the width of the energy level of the ground state of pionic deuterium. We show that the experimental data on the width satisfy these constraints. This testifies an indirect measurement of the recommended value of the astrophysical factor for the solar proton burning in terrestrial laboratories in terms of the width of the energy level of the ground state of pionic deuterium.
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    Wootters’ distance revisited: a new distinguishability criterium (2005)
    Springer
    The European physical journal 32 (2005), S. 413-419 
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    ISSN: 1434-6079
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. The notion of distinguishability between quantum states has shown to be fundamental in the frame of quantum information theory. In this paper we present a new distinguishability criterium by using a information theoretic quantity: the Jensen-Shannon divergence (JSD). This quantity has several interesting properties, both from a conceptual and a formal point of view. Previous to define this distinguishability criterium, we review some of the most frequently used distances defined over quantum mechanics’ Hilbert space. In this point our main claim is that the JSD can be taken as a unifying distance between quantum states.
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    Three-step laser excitation of the 6p3/2ns, nd, ng autoionizing Rydberg levels via the 6p5f 1/2[5/2]2 level of lead (2005)
    Springer
    The European physical journal 32 (2005), S. 271-276 
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    ISSN: 1434-6079
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. Odd parity autoionizing Rydberg levels of atomic lead in the energy region above the 6p1/2 ionization threshold have been investigated using three-step laser excitation in conjunction with an atomic beam apparatus. The 6p3/2ns (J = 1, 2), 6p3/2nd (J = 1, 2, 3) and 6p3/2ng (J = 2, 3) levels have been observed from the 6p5f 1/2[5/2]2 intermediate level. Energy values and FWHM of forty levels belonging to the 6p3/2ns, 6p3/2nd and 6p3/2ng configurations are presented. Six levels based on the 6p3/2ng (5, 13 ≤n ≤15) configurations and three levels attached to the 6p3/28d configuration are reported for the first time. The present study of the low-lying autoionizing levels attached to the 6p3/25g (J = 2, 3) configuration completes the series adjacent to the 6p1/2 limit.
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    Dynamics of a charged particle in a linearly polarized traveling wave (2005)
    Springer
    The European physical journal 32 (2005), S. 361-376 
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    ISSN: 1434-6079
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. The basic physical processes in laser-matter interaction, up to $10^{17}~{\rm W/cm}^2$ (for a neodymium laser) are now well understood, on the other hand, new phenomena evidenced in PIC code simulations have to be investigated above $10^{18}~{\rm W/cm}^2$ . Thus, the relativistic motion of a charged particle in a linearly polarized homogeneous electromagnetic wave is studied, here, using the Hamiltonian formalism. First, the motion of a single particle in a linearly polarized traveling wave propagating in a non-magnetized space is explored. The problem is shown to be integrable. The results obtained are compared to those derived considering a cold electron plasma model. When the phase velocity is close to c, it is shown that the two approaches are in good agreement during a finite time. After this short time, when the plasma response is taken into account no chaos take place at least when considering low densities and/or high wave intensities. The case of a charged particle in a traveling wave propagating along a constant homogeneous magnetic field is then considered. The problem is shown to be integrable when the wave propagates in vacuum. The existence of a synchronous solution is shown very simply. In the case when the wave propagates in a low density plasma, using a simplifying Lorentz transformation, it is shown that the system can be reduced to a time-dependent system with two degrees of freedom. The system is shown to be nonintegrable, chaos appears when a secondary resonance and a primary resonance overlap. Finally, stochastic instabilities are studied by considering the motion of one particle in a very high intensity wave perturbed by one or two low intensity traveling waves. Resonances are identified and conditions for resonance overlap are studied.
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    A theoretical scheme for generation of nonlinear coherent states in a micromaser under intensity-dependent Jaynes-Cummings model (2005)
    Springer
    The European physical journal 32 (2005), S. 397-408 
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    ISSN: 1434-6079
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. In this paper we propose a theoretical scheme to show the possibility of generating various families of nonlinear (f-deformed) coherent states of the radiation field in a micromaser. We show that these states can be provided in a lossless micromaser cavity under the weak Jaynes-Cummings interaction with intensity–dependent coupling of large number of individually injected two-level atoms in a coherent superposition of the upper and lower states. In particular, we show that the so-called nonlinear squeezed vacuum and nonlinear squeezed first excited states, as well as the even and odd nonlinear coherent states can be generated in a two-photon micromaser.
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    Diffraction of three-dimensional beams in uniaxial media (2005)
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    The European physical journal 32 (2005), S. 377-381 
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    ISSN: 1434-6079
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. Within here we make an analysis of two and three-dimensional beams synthesized by extraordinary waves that propagate in uniaxial media. A relation between the geometric place of the first interference maxima and the energy flow direction is established. In addition, we determine that three-dimensional extraordinary symmetrical beams can be obtained from two two-dimensional ones that are not to be necessarily orthogonal.
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    Obtaining colder ensembles of free clusters by using evaporation and recoil (2005)
    Springer
    The European physical journal 32 (2005), S. 339-345 
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    ISSN: 1434-6079
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. We describe a theoretical model which treats the effects of evaporation-induced recoil on the mass and temperature distributions of a collimated beam of small neutral clusters emitted by a hot-nozzle source. The model incorporates two important consequences of in-flight cluster fragmentation processes. One is the well-known statistical evaporation of atoms and dimers accompanied by cluster size redistribution and cooling, and the other is the accompanying mechanical recoil of the fragments. We predict that the filtering effect introduced by cluster recoil can be used to an advantage by separating out the off-axis cluster population. This fraction will have a significantly narrower and colder distribution of internal temperatures than the on-axis ensemble.
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    Excessive hydrogen and deuterium Balmer lines broadening in a hollow cathode glow discharges (2005)
    Springer
    The European physical journal 32 (2005), S. 347-354 
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    ISSN: 1434-6079
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. Results of a Doppler spectroscopy study of hydrogen and deuterium Balmer lines in the stainless steel and copper hollow cathode glow discharge, operated in pure hydrogen, deuterium and mixtures of inert gases with hydrogen, are reported. For all gases and gas mixtures plasma observations perpendicular to electric field revealed the excessively large Doppler broadening. By changing mode of glow discharge operation, the Doppler broadened line profiles in helium-hydrogen mixture are recorded parallel to the discharge electric field as well. The excessively broadened part of the Hα line profile is shifted towards blue or red wavelength by changing the direction of electric field vector. The presence of large excessive Balmer lines broadening in pure hydrogen and in its gas mixture with neon as well as shifting of the excessively broadened part of line profile by means of electric field is in contradiction with the resonance transfer model proposed by Mills et al. in several publications, see e.g. [IEEE Trans. Plasma Sci. 31, 338 (2003)].  
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1140/epjd/e2004-00192-1
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    Radiative lifetimes of some excited states of neutral xenon (2005)
    Springer
    The European physical journal 32 (2005), S. 285-288 
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    ISSN: 1434-6079
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. The radiative lifetimes of ten levels belonging to the nf (n=4-7) and three levels belonging to the ns (n=8,9) configuration of XeI have been measured using the high frequency deflection technique together with a delayed coincidence single-photon counting arrangement. Lifetimes of some of the levels have been measured for the first time. The results have been compared with other experimental and theoretical values.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1140/epjd/e2005-00002-4
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  • 196
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    Ion charge state distributions following K-shell ionization in atoms (2005)
    Springer
    The European physical journal 32 (2005), S. 277-283 
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    ISSN: 1434-6079
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. Ion charge state distributions and the mean charge state following K-shell ionization in atoms are calculated. The Monte Carlo method is applied to calculate the vacancy cascades after K-shell vacancy creation. The radiative and non-radiative transitions are calculated for singly ionized atoms. The transition rates for multi-ionized atoms are obtained using a statistical scaling procedure based on the transition probabilities for singly ionized atoms. The electron shake-off process due to the change of atomic potential, which occurs from core hole production and de-excitation decays, is considered in the calculation. The present results agree well with the available experimental values.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1140/epjd/e2005-00003-3
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    The threshold electron impact spectrum of H2O (2005)
    Springer
    The European physical journal 32 (2005), S. 319-328 
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    ISSN: 1434-6079
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. The threshold electron spectrum of H2 O was obtained using a high resolution electron impact spectrometer combined with the penetrating field method for scattered electrons with energies close to zero eV. The valence, triplet Rydberg states, as well as the resonances were identified and are discussed in the energy region 5.2–14.3 eV. The threshold spectrum confirms the influence of resonances on the enhancement of the intensity of some Rydberg states above 10 eV. The vibrational spacing of the observed transitions of the Rydberg states indicates that the water molecule is excited in the symmetric stretching mode.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1140/epjd/e2005-00001-5
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    Insights into positron annihilation lifetime spectroscopy by molecular dynamics simulations (2005)
    Springer
    The European physical journal 32 (2005), S. 289-297 
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    ISSN: 1434-6079
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. The relationship between free-volume properties measured from positron annihilation lifetime spectroscopy (PALS) and calculated from molecular dynamics simulations has been investigated for glassy and liquid glycerol in the temperature range 150–400 K. A virtual probing procedure has been developed to retrieve information on the basic free-volume properties of the simulated microstructures, i.e. mean cavity volume and free-volume cavity fractions. Our data leads us to infer on the occurrence of experimentally non-detectable small cavities with mean equivalent radius of 1.8–1.9 Å between 250 and 275 K. The size of these limiting cavities is found to be temperature dependent, being smaller at low temperatures. At high temperatures, above a characteristic PALS temperature Tb2L , the formation of very large cavities is predicted. This finding suggests that, when the dimension of the holes in the system exceeds a given value, the PALS measurements become unable to catch the complete structural information and phenomena of dynamical origin enter into play in the PALS signal decay. The calculated number of cavities is found to be almost independent on the temperature from the glassy up to the liquid phase, thus furnishing a certain support to theoretical models proposed to evaluate the free-volume cavity fractions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1140/epjd/e2005-00015-y
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    Thermal entanglement in two qutrits system (2005)
    Springer
    The European physical journal 32 (2005), S. 409-412 
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    ISSN: 1434-6079
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. The thermal entanglement in a two-qutrit system with two spins coupled by exchange interaction is investigated in terms of the measure of entanglement called “negativity”. It is found that the thermal entanglement is present and evolvements symmetrically between both ferromagnetic and antiferromagnetic exchange couplings with the temperature. Moreover the critical temperature at which the negativity vanishes increases with the exchange coupling constant J. From the temperature and magnetic field dependences we demonstrate that the temperature and the magnetic field can affect the feature of the thermal entanglement significantly.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1140/epjd/e2004-00194-y
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    Smoothed Wigner functions: a tool to resolve semiclassical structures (2005)
    Springer
    The European physical journal 32 (2005), S. 355-359 
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    ISSN: 1434-6079
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. The Wigner and Husimi distributions are the usual phase space representations of a quantum state. The Wigner distribution has structures of order ħ2. On the other hand, the Husimi distribution is a Gaussian smearing of the Wigner function on an area of size ħ and then, it only displays structures of size ħ. We have developed a phase space representation which results a Gaussian smearing of the Wigner function on an area of size ħσ, with σ≥1. Within this representation, the Husimi and Wigner functions are recovered when σ=1 and $ \sigma \gtrsim 2 $ respectively. We treat the application of this intermediate representation to explore the semiclassical limit of quantum mechanics. In particular we show how this representation uncover semiclassical hyperbolic structures of chaotic eigenstates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1140/epjd/e2004-00189-8
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