ALBERT

Notes: Abstract: The friction between the walls of multi-wall carbon nanotubes is shown to be extremely low in general, with important details related to the specific choice of the walls. This is governed by a simple expression revealing that the phenomenon is a profound consequence of the specific symmetry breaking: super-slippery sliding of the incommensurate walls is a Goldstone mode. Three universal principles of tribology, offering a recipe for lubricant selection are emphasized.

Notes: Abstract: A new kind of memory effect on low frequency dielectric measurements on plexiglass (PMMA) is described. These measurements show that cooling and heating the sample at constant rate give an hysteretic dependence on temperature of the dielectric constant ε. A temporary stop of cooling produces a downward relaxation of ε. Two main features are observed (i) when cooling is resumed ε goes back to the values obtained without the cooling stop (i.e. the low temperature state is independent of the cooling history) (ii) upon reheating ε keeps the memory of all the cooling stops (Advanced memory). The dependence of this effect on frequency and on the cooling rate is analyzed. The memory deletion is studied too. Finally the results are compared with those of similar experiments done in spin glasses and with the famous experiments of Kovacs.

Notes: Abstract: We present a quantum mechanical model of the magnetoresistance in ferromagnetic tunnel junctions artificially doped by the introduction of layers of impurities in the middle of the barrier. The electron transport across the barrier is described by a combination of direct tunneling, tunneling assisted by spin-conserving scattering and tunneling assisted by spin-flip scattering. With this model, we interpret recent experimental results concerning the dependence of the TMR amplitude on the amount of impurities in the barrier and on temperature.

Notes: Abstract: We investigate stationary and travelling wave solutions of the classical one-dimensional transverse field Ising model. Results are given on the existence, shape and stability of kink solutions and periodic solutions. We review recent analytical results (e.g., the proof of existence of a one-parameter family of stationary kink solutions and the proof of existence of travelling wave kink solutions with nonzero velocity c≠ 0) and extend them by the use of numerical methods. Small oscillations arising in the tails of travelling kink solutions are investigated numerically. In the end, stability analysis puts some light on pinning effects.

Notes: Abstract: We have measured the zero field and field cooled magnetization of the lightly oxygen doped Cu-rich La2CuO 4 + δ in a wide temperature range (5 K to 350 K). The data together with the evolution of the magnetic hysteresis loop suggest that the ferromagnetism with Curie temperature of 280 K coexists with superconductivity below the transition temperature ∼ 34 K. The coexistence occurs in the hole-rich clusters of size ? 150 nm, which are electronic phase separated from the hole-poor antiferromagnetic background.

Notes: Abstract: Superconductors put into rotation develope a spontaneous internal magnetic field (the “London field”). In this paper Ginzburg Landau equations for order parameter, field, and current distributions for superconductors in rotation are derived. Two simple examples are discussed: the massive cylinder and the “Little and Parks geometry”: a thin film of superconducting material deposited on a cylinder of normal material. A dependence of T c on rotational frequency is predicted. The magnitude of the effect is estimated and should be observable.

Notes: Abstract: The evaluation of the total force of magnetic origin acting upon a body in a stationary magnetic field is often carried out using the so-called magnetic energy (or co-energy) method, which is based on the derivation of the magnetic energy (or co-energy) with respect to a virtual rigid displacement of the considered body. The application of this method is usually justified by resorting to the energy conservation principle, written in terms both of electrical and of mechanical quantities. In this paper we shall re-examine the whole matter in the context of classical thermodynamics, in order to obtain a more comprehensive and general proof of the validity of the energy (or co-energy) approach and to point out its limitations. Two typical configurations will be discussed; in the first one, the field sources are represented by conducting bodies carrying free currents, whereas in the second one a permanent magnet creates the driving field. All magnetic materials are assumed to be non-hysteretic and permanent magnets are represented by means of the well-known linear model in the second quadrant of the (B,H) plane.

Notes: Abstract: The weak coupling instabilities of a two dimensional Fermi system are investigated for the case of a square lattice using a Wilson renormalization group scheme to one loop order. We focus on a situation where the Fermi surface passes through two saddle points of the single particle dispersion. In the case of perfect nesting, the dominant instability is a spin density wave but d-wave superconductivity as well as charge or spin flux phases are also obtained in certain regions in the space of coupling parameters. The low energy regime in the vicinity of these instabilities can be studied analytically. Although saddle points play a major role (through their large contribution to the single particle density of states), the presence of low energy excitations along the Fermi surface rather than at isolated points is crucial and leads to an asymptotic decoupling of the various instabilities. This suggests a more mean-field like picture of these instabilities, than the one recently established by numerical studies using discretized Fermi surfaces.

Notes: Abstract: The ac-transport properties of a one-dimensional quantum dot with non-Fermi liquid correlations are investigated. It is found that the linear photoconductance is drastically influenced by the interaction. While for weak interaction it shows peak-like resonances, in the strong interaction regime it assumes a step-like behavior. In both cases the photo-transport provides precise informations about the quantized plasmon modes in the dot. Temperature and voltage dependences of the sideband peaks are treated in detail. Characteristic Luttinger liquid power laws are found.

Notes: Abstract: A unification of recently proposed models describing population dynamics is presented. We study the effect of different factors, like environmental conditions, concentration of individuals in a given area and migration strategies, on population dynamics. Moreover, we show that a population occupying a smaller area is more susceptible to extinction, which is a well known biological fact. We solve the model using Monte Carlo simulations and the mean-field approach. Constructing flow diagrams we find the optimal strategy in population dynamics.

Notes: Abstract: According to contemporary crystal growth theories, crystals are bound by low-index faces which are the most slowly growing. However, high-index faces are observed in crystal habits more and more often. In this paper the growth of high-index faces is analysed from a crystallographic perspective. It is shown that the crystallographic structure of a given crystal, expressed by the trigonometric function of appropriate interfacial angles, influences to great degree the crystallisation process and the morphology of crystals, in particular the behaviour of high-index faces. Additionally, it is concluded that at particular crystallographic structure of a crystal, a given high-index face may exist in the habit and develop its size, although it grows much faster than the neighbouring faces.

Notes: Abstract: Vortex-antivortex pairs in 2D easy-plane ferromagnets have characteristics of solitons in two dimensions. We investigate numerically and analytically the dynamics of such vortex pairs. In particular we simulate numerically the head-on collision of two pairs with different velocities for a wide range of the total linear momentum of the system. If the momentum difference of the two pairs is small, the vortices exchange partners, scatter at an angle depending on this difference, and form two new identical pairs. If it is large, the pairs pass through each other without losing their identity. We also study head-tail collisions. Two identical pairs moving in the same direction are bound into a moving quadrupole in which the two vortices as well as the two antivortices rotate around each other. We study the scattering processes also analytically in the frame of a collective variable theory, where the equations of motion for a system of four vortices constitute an integrable system. The features of the different collision scenarios are fully reproduced by the theory. We finally compare some aspects of the present soliton scattering with the corresponding situation in one dimension.

Notes: Abstract: The network of Barabasi and Albert, a preferential growth model where a new node is linked to the old ones with a probability proportional to their connectivity, is applied to Brazilian election results. The application of the Sznajd rule, that only agreeing pairs of people can convince their neighbours, gives a vote distribution in good agreement with reality

Notes: Abstract: The simulation of the transition sequence of superheated Type I superconducting granules (SSG) in disordered suspensions when an external magnetic field is slowly increased from zero has been studied. Simulation takes into account diamagnetic interactions and the presence of surface defects. Results have been obtained for the transition sequence and surface fields distribution covering a wide range of densities. These results are compared with previous analytical perturbative theory, which provides qualitative information on transitions and surface magnetic fields during transitions, but with a range of validity apparently limited to extremely dilute samples. Simulations taking into account the complete diamagnetic interactions between spheres appear to be a promising tool in interpreting SSG experiments, in applications such as particle detectors, and in some fundamental calculations of Solid State Physics.

Notes: This coming year, 2002, will already be the fifth year of publication for the European Physical Journal B, EPJ B. The journal is still influenced by the centennial tradition of its parent journals, Il Nuovo Cimento (section B), Journal de Physique and Zeitschrift für Physik B, which have formed the basis of the merger, EPJ B is rapidly expanding and has now managed to capture the interest of eleven European Physical Societies. We are happy to announce that in 2001 both the Polish Physical Society and the Roland Eötvös Physical Society from Hungary were included as part of our Scientific Advisory Committee. All information regarding the various sections of EPJ can be seen by accessing the Web address: http://www.eurphysj.org/ 2001 has been a healthy year for EPJ B with interesting physics, increasing support from the scientific community, an increase in the overall number of submissions, a growing readership and continuously improving performance of the editorial procedures. With high quality physics already published we continue to be a generalist physics journal focusing on specific themes of current interest. A special topic has also been emphasised in 2001 with a topical issue on Interdisciplinary Physics based on invited papers at the conference APFA-2 (Applications of Physics to Financial Analysis) in Liège, Belgium. This topic will be further emphasised again in 2002. Thanks to the competence of the Editorial Office and the efficiency of the publishers, we have reached a highly competitive publication time (with an average of 2.5 months between the acceptance and the publication of articles). As for the evaluation process, two or sometimes three referees are asked to advise the associate editors, therefore contributing to a thorough evaluation and often providing authors with valuable suggestions, with three quarters of the manuscripts accepted in less than four months (including revision time). This editorial is a good opportunity to thank very warmly all our colleagues, associate editors and their referees who have devoted time and effort to perform fair and constructive scientific evaluations. The quality of the journal has been recognised by the ISI impact factor since it has climbed from the twelfth up to the fifth rank from 1999 to 2000. EPJ B is now ranked as the first European-based journal in Condensed Matter Physics. Two new associate editors have joined the Editorial Board in 2001, M. Dacorogna (Interdisciplinary Physics) and F. Mila (Solid and Condensed Matter Physics), both of whom are located in Switzerland. More new associate editors are expected to join us in 2002. This will expand both the topical and geographical coverage of the journal. Let us remind you about the existence of the Rapid Notes which have been quite successful in EPJ B. These notes provide a means of publication of short papers, less than four printed pages, describing important advances, within three months of their reception by the Editorial Office. Authors, referees and the editorial office benefit from an improved inquiry service (IS) or manuscript management system (MMS) which allow on-line submissions, on-line response from referees as well as the follow up of the evaluation and production processes by the authors. Finally we are happy to announce that from now onwards the DOI referencing procedure will be used (http://www.doi.org) allowing a means of persistent electronic referencing to the on-line first version of the articles. All in all we have good reasons to be proud of this European-based journal with a world-wide distribution. All colleagues on the editorial staff can assure you that they will do all that is possible to spread high level scientific information and to please both its authors and readers. We invite you to remain with us, publish some of your best papers in EPJ B and read the journal on a regular basis. As always at the turn of the year, we wish you many outstanding results, many exciting discoveries and a Happy New Year. S. Grossmann, D. Jérome and A. Paoletti

Notes: Abstract: Discontinuous magnetic metal/insulator multilayers are formed of equally spaced layers of magnetic particles embedded in an insulating matrix. Their electronic transport properties result from spin-polarized electron tunneling and Coulomb blockade effect. The current-in-plane (CIP) and current-perpendicular-to plane (CPP) resistances change by several orders of magnitude when the thicknesses of the metallic or insulating layers are varied. Calculations of the shape of the current lines in these multilayers are presented. It is shown that pure CIP or CPP transport occur in these systems only when the CIP or CPP resistances are very different in magnitude. If the two resistances are of the same order of magnitude, then the measured transport properties in both geometries are a combination of CIP and CPP transport.

Notes: Abstract: A self-organized branching process is introduced to describe one-dimensional rice-pile model with stochastic topplings. Although the branching processes are generally expected to describe well high-dimensional systems, our modification highlights some of the peculiarities present in one dimension. We find analytically that the crossover behavior from the trivial one-dimensional BTW behaviour to self-organized criticality is characterised by a power-law distribution of avalanches. The finite-size effects, which are crucial to the crossover, are calculated.

Notes: Abstract: We report a theoretical analysis of the phonon thermal conductance, κ(T), for single wall carbon nanotubes (SWCN). In a range of low temperatues up to 100 K, κ(T) of perfect SWCN is found to increase with temperature, approximately, in a parabolic fashion. This is qualitatively consistent with recent experimental measurements where the tube-tube interactions are negligibly weak. When the carbon-carbon bond length is slightly varied, κ(T) is found to be qualitatively unaltered which implies that the anharmonic effect does not change the qualitative behavior of κ(T).

Notes: Abstract: The electronic and magnetic properties of Pu monopnictides and monochalcogenides, PuX (X = N, P, As, Sb, Bi, O, S, Se, Te, Po), are studied using the self-interaction-corrected local spin-density approximation. This approach allows for an integer number of f-states to be localized, while the remaining f-electron degrees of freedom are available for band formation. By varying the relative proportions of localized and delocalized f-states, the energetically most favourable (groundstate) configuration can be established. We show that the experimental data can be interpreted in terms of the coexistence of both localized and delocalized f-states.

Notes: Abstract: Growth, structural and magnetic properties of cobalt island structures grown by molecular beam epitaxy on 4 nm thick island shaped Ru buffers are studied. The islands are characterized by a narrow distribution of sizes, and are separated on average by spacing of around one hundred nanometers. Growth of the islands into continuous films is found to proceed in three well defined stages, and corresponding magnetic behaviors are identified. The particles formed in the first stage of growth appear to be similar in shape and size, and their magnetic behavior suggest the presence of superparamagnetism. Particles in the second stage of growth are ferromagnetic and display a reorientation transition of their magnetization out of the film plane, consistent with that seen in patterned magnetic dot arrays. Particles coalesce in the last stage of growth and magnetic properties of continuous films are observed.

Notes: Abstract: We studied the changes in the electronic structure of SrTi1-xRuxO3 across the metal-insulator transition. The parent compound, SrTiO3, is a well known diamagnetic insulator; whereas the doped compound, SrTi1-xRuxO3, becomes a ferromagnetic metal above x C = 0.35. The techniques used in the study were photoemission (PES) and O 1 s X-ray absorption (XAS) spectroscopy. The experimental spectra were analyzed in terms of band structure and Hubbard model calculations. The PES and XAS spectra of SrTi1-xRuxO3 show the Ru 4 d bands growing in the band gap of SrTiO3 . The analysis in terms of the Hubbard model indicates that the Ti 3 d and Ru 4 d bands are mostly decoupled. This suggests that the metal-insulator transition is a percolation transition like that of metals embedded in a rare gas matrix. Electron correlation effects are present in this system, but they do not seem to play a major role in the transition.

Notes: Abstract: Highway traffic as simulated with a simple cellular automata model has been analysed in a search for self-similarity in the behaviour of car density and car flow as a function of space. Fractal dimensions between 1.5 and 1.6, depending on the simulation characteristics, have been measured with a box counting algorithm. The self-similarity spans over about 2 orders of magnitude. A comparison with experimental data is suggested.

Notes: Abstract. We discuss rare kaon decays that violate charged-lepton flavour conservation in supersymmetric theories with and without R parity, in view of possible experiments using an intense proton source as envisaged for a neutrino factory. In the minimal supersymmetric standard model, such decays are generated by box diagrams involving charginos and neutralinos, but the limits from $\mu \rightarrow e \gamma, \mu$ –e conversion and $\Delta m_K$ constrain the branching ratios to challengingly small values. However, this is no longer the case in R-violating theories, where such decays may occur at tree level at rates close to the present experimental limits. Within this framework, we obtain bounds on products of $LL\bar{E}$ and $LQ\bar{D}$ operators from the experimental upper limits on $K^0 \rightarrow \mu^\pm e^\mp$ and $K^{\pm,0} \rightarrow \pi^{\pm,0} \mu^\pm e^\mp$ decays. We also note the possibility of like-sign lepton decays $K^\pm \rightarrow \pi^\mp \ell^\pm \ell^\pm$ in the presence of non-zero $\tilde{b}_{\mathrm{L}}$ – $\tilde{b}_{\mathrm{R}}$ mixing. We conclude that rare kaon decays violating charged-lepton flavour conservation could be an interesting signature of R violation.

Notes: Abstract. A search for first generation scalar and vector leptoquarks (LQ) as well as for squarks ( $\tilde{\mbox{q}}$ ) in R-parity violating SUSY models with the direct decay of the $\tilde{\mbox{q}}$ into Standard Model particles has been performed using e $^+$ e $^-$ collisions collected with the OPAL detector at LEP at an e $^+$ e $^-$ centre-of-mass energy $\sqrt{s_{\rm ee}}$ of 189 GeV. The data correspond to an integrated luminosity of about 160 pb $^{-1}$ . The dominant process for this search is $\mbox{eq}\to\LQ/\tilde{\mbox{q}}\to\mbox{eq},\nu\mbox{q}$ , where a photon, which has been radiated by one of the beam electrons, serves as a source of quarks. The numbers of selected events found in the two decay channels are in agreement with the expectations from Standard Model processes. This result allows to set lower limits at the 95% confidence level on the mass of first generation scalar and vector leptoquarks, and of squarks in R-parity violating SUSY models. For Yukawa couplings $\lambda$ to fermions larger than $\sqrt{4\pi\alpha_{\rm em}}$ , the mass limits range from 121 GeV $/c^2$ to $175$ GeV $/c^2$ ( $149$ GeV $/c^2$ to $188$ GeV $/c^2$ ) depending on the branching ratio $\beta$ of the scalar (vector) leptoquark state. Furthermore, limits are set on the Yukawa couplings $\lambda$ for leptoquarks and $\lambda'_{1jk}$ for squarks, and on $\beta$ as a function of the scalar leptoquark/squark mass.

Notes: Abstract. In the framework of the constrained minimal supersymmetric standard model (CMSSM) we discuss the impact of the pseudo-scalar Higgs boson in delineating regions of the parameters which are consistent with cosmological data and E821 data on the anomalous magnetic moment of the muon. For the large values of the parameter $\tan \beta 〉 50$ , cosmologically allowed corridors of large $m_0, M_{1/2}$ are opened, due to the s-channel pseudo-scalar exchange in the pair annihilation of the lightest of the neutralinos to $b \bar{b}$ or $\tau \bar{\tau}$ , which dominates in this region. However, no such corridors are found for values $\tan \beta 〈 50 $ . Combining cosmological and E821 data puts severe upper limits on the sparticle masses. We find that at LHC, but even at a $e^+e^-$ linear collider with center of mass energy $s^{1/2} = 800$ GeV, such as TESLA, supersymmetry can be discovered, if it is based on the CMSSM.

Notes: Abstract. In this work we report about the effect that the improved knowledge of electroweak radiative corrections, via the recent calculations of four-fermion processes with ${\cal O}(\alpha)$ corrections in double pole approximation, has on WW physics at LEP2. Particular emphasis is given to the effects on differential distributions and their impact on the experimental observables. This study is based on generator comparisons using the new codes from the 2000 LEP2 Montecarlo workshop and allows new, important insights on the effects full radiative corrections have on W physics observables. The results presented here explain why it is so important to take these new calculations into account for precision measurements at LEP2.

Notes: Abstract. We compute the low energy threshold corrections to neutrino masses and mixing in the standard model (SM) and its minimal supersymmetric version, using the effective theory technique. We demonstrate that they stabilize the results for neutrino masses and mixing with respect to the choice of the scale to which the renormalization group (RG) equation is integrated. (This confirms the correctness of the recent re-derivation of the RGE for the SM in hep-ph/0108005.) Since, as is known, those corrections are potentially very important for phenomenology we derive for them the explicit formulae that can be applied to specific models of neutrino masses and mixing.

Notes: Abstract. A simple model is presented which interpolates between the DGLAP and BFKL regimes in deep inelastic ep scattering. This model is based on the CCFM and LDC models, and it is simple enough to provide an intuitive picture of the transition region between the two domains. Results are presented for both fixed and running coupling; for fixed coupling the transition between the domains occurs at a constant ratio between $\ln k_\perp^2$ and $\ln 1/x$ , while for a running coupling it occurs for constant ratio between $\ln \ln k_\perp^2$ and $\ln 1/x$ .

Notes: Abstract. The method of stochastic quantization of Parisi–Wu is extended to include spinor fields obeying the generalized statistics of order two consistent with the weak locality requirement. Appropriate Langevin and Fokker–Planck equations are constructed using paragrassmann variables, which give rise to two fields with different masses in the equilibrium limit, in agreement with the results of the canonical quantization procedure. The connection between the stochastic quantization method and conventional Euclidean field theory is established through Klein transformations.

Notes: Abstract. A recently proposed modified perturbative expansion for QCD incorporating gluon condensation is employed to evaluate the quark and gluon self-energy corrections in first approximation. The results predict mass values of 1/3 of the nucleon mass for the light quarks u, d, and s and a monotonously growing variation with the current mass. The only phenomenological input is that $\langle G^2\rangle $ is evaluated up to order $g^2$ as a function of the unique parameter C defining the modified propagator, and then C is fixed to give a current estimate of $\langle g^2G^2\rangle $ . The light quarks u and d as a result are found to be confined and the s, c, b and t ones show damped propagation modes, suggesting a model for the large differences in stability between the nucleons and the higher resonances. The above properties of quark modes diverge from the fully confinement result following from the similar gluon propagator previously considered by Munczek and Nemirovski. On the other hand, the condensate effects on the gluon self-energy furnish a tachyonic mass shell as predicted by the Fukuda analysis of gluon condensation in QCD.

Notes: Abstract. We study the double-diffractive production of various heavy systems (e.g. Higgs, dijet, $t\bar{t}$ and SUSY particles) at LHC and Tevatron collider energies. In each case we compute the probability that the rapidity gaps, which occur on either side of the produced system, survive the effects of soft rescattering and QCD bremsstrahlung effects. We calculate both the luminosity for different production mechanisms, and a wide variety of subprocess cross sections. The results allow numerical predictions to be readily made for the cross sections of all these processes at the LHC and the Tevatron collider. For example, we predict that the cross section for the exclusive double-diffractive production of a 120 GeV Higgs boson at the LHC is about 3 fb, and that the QCD background in the $b\bar{b}$ decay mode is about 4 times smaller than the Higgs signal if the experimental missing-mass resolution is 1 GeV. For completeness we also discuss production via $\gamma\gamma$ or WW fusion.

Notes: Abstract. We compute the couplings $DD^*\pi$ , $D_1D^*\pi, D^*D^*\pi$ and $D_1 D_1\pi$ using QCD sum rules. These couplings are important inputs in the meson-exchange model calculations used to estimate the amount of $J/\psi$ absorption due to pions and rho mesons in heavy-ion collisions. Our sum rules are constructed at the first order in the pion momentum $p_\mu$ , which give the couplings that are not trivially related to the soft-pion theorem. Our calculated couplings, which somewhat depend upon the values of the heavy meson decay constants, are $g_{DD^*\pi}=8.2 \pm 0.1$ , $g_{D_1 D^* \pi} = 15.8 \pm 2{\mathrm{ GeV}}$ , $g_{D^* D^* \pi}= 0.3 \pm 0.03$ and $g_{D_1 D_1 \pi}= 0.17 \pm 0.04$ .

Notes: Abstract. The results concerning the $e^+e^-$ production in peripheral highly relativistic heavy-ion collisions presented in a recent paper by Baltz et al. are rederived in a very straightforward manner. It is shown that the solution of the Dirac equation directly leads to the multiplicity, i.e. to the total number of electron–positron pairs produced by the electromagnetic field of the ions, whereas the calculation of the single pair production probability is much more involved. A critical observation concerns the unsolved problem of seemingly absent Coulomb corrections (Bethe–Maximon corrections) in pair production cross sections. It is shown that neither the inclusion of the vacuum–vacuum amplitude nor the correct interpretation of the solution of the Dirac equation concerning the pair multiplicity is able the explain (from a fundamental point of view) the absence of Coulomb corrections. Therefore the contradiction has to be accounted to the treatment of the high energy limit.

Notes: Abstract. We construct the effective chiral Lagrangian for chiral perturbation theory in the mesonic odd-intrinsic-parity sector at order $p^6$ . The Lagrangian contains 24 in principle measurable terms and no contact terms for the general case of $N_f$ light flavors, 23 terms for three and 5 for two flavors. In the two flavor case we need a total of 13 terms if an external singlet vector field is included. We discuss and implement the methods used to reduce to a minimal set. The infinite parts needed for renormalization are calculated and presented as well.

Notes: Abstract. A generalized Dick model with a potential term is discussed. The solution originating from a static, point-like, color source is found to have a confining part. A comparison with a wide spectrum of phenomenological quark–antiquark potentials is presented.

Notes: Abstract. Within a Two-Higgs-Doublet Model (2HDM) a search for a light Higgs boson in the mass range of 4–12 GeV has been performed in the Yukawa process $\mathrme^+ \mathrme^-\rightarrow \mathrm{b}\bar{\mathrm{b}}\mathrm{A}/\mathrm{h}\rightarrow\mathrm{b} \bar{\mathrm{b}}\tau^+\tau^-$ , using the data collected by the OPAL detector at LEP between 1992 and 1995 in $\mathrme^+ \mathrme^-$ collisions at about 91 GeV centre-of-mass energy. A likelihood selection is applied to separate background and signal. The number of observed events is in good agreement with the expected background. Within a CP-conserving 2HDM type II model the cross-section for Yukawa production depends on $\xi^{\mathrm{A}}_d=|\tan\beta|$ and $\xi^{\mathrm{h}}_d=|\sin\alpha/\cos\beta|$ for the production of the CP-odd A and the CP-even h, respectively, where $\tan\beta$ is the ratio of the vacuum expectation values of the Higgs doublets and $\alpha$ is the mixing angle between the neutral CP-even Higgs bosons. From our data 95% C.L. upper limits are derived for $\xi^{\mathrm{A}}_d$ within the range of 8.5 to 13.6 and for $\xi^{\mathrm{h}}_d$ between 8.2 to 13.7, depending on the mass of the Higgs boson, assuming a branching fraction into $\tau^+\tau^-$ of 100%. An interpretation of the limits within a 2HDM type II model with Standard Model particle content is given. These results impose constraints on several models that have been proposed to explain the recent BNL measurement of the muon anomalous magnetic moment.

Notes: Abstract. We accomplish our efforts to obtain predictions for all four–fermion final states of $e^+ e^-$ –annihilation and the corresponding bremsstrahlung reactions which are possible in the framework of the Standard Model. For this purpose we have developed a program ee4 f$\gamma$ . Our predictions are valid for fermions of arbitrary masses and we can obtain results for total cross sections without any collinear cut. Keeping exact fermion masses is of course required for top quark production. We give a detailed phenomenological analysis of fermion mass effects and real photon radiation for all channels of four–fermion production at LEP-II and next linear collider energies.

Notes: Abstract. We study B meson decays to two charmless baryons in the diquark model, including strong and electroweak penguins as well as the tree operators. It is shown that penguin operators can enhance $\bar{B} \rightarrow{\vec B}_s \bar{{\vec B}}$ considerably, but affect $\bar{B} \rightarrow{\vec B}_1 \bar{{\vec B}}_2$ only slightly, where ${\vec B}_{(1,2)}$ and ${\vec B}_s$ are non-strange and strange baryons, respectively. The $\gamma$ dependence of the decay rates due to tree–penguin interference is illustrated. In principle, some of the ${\vec B}_s \bar{{\vec B}}$ modes could dominate over ${\vec B}_1 \bar{{\vec B}}_2$ for $\gamma 〉 90^\circ$ , but in general the effect is milder than their mesonic counterparts. This is because the $O_6$ operator can only produce vector but not scalar diquarks, while the opposite is true for $O_1$ and $O_4$ . Predictions from the diquark model are compared to those from the sum rule calculation. The decays $\bar{B} \rightarrow{\vec B}_s \bar{{\vec B}}_s$ and inclusive baryonic decays are also discussed.

Notes: Abstract. Inelastic QED processes, the cross sections of which do not drop with increasing energy, play an important role at high-energy colliders. Such reactions have the form of two-jet processes with the exchange of a virtual photon in the t-channel. We consider them in the region of small scattering angles $ m/E \lesssim \theta 〈〈 1$ , which yields the dominant contribution to their total cross sections. A new effective method is presented and applied to QED processes with emission of real photons to calculate the helicity amplitudes of these processes. Its basic idea is similar to the well-known equivalent-lepton method. Compact analytical expressions for those amplitudes up to $e^8$ are derived omitting only terms of the order of $m^2/E^2, \theta^2, \theta m/E$ and higher order. The helicity amplitudes are presented in a compact form in which large compensating terms are already cancelled. Some common properties for all jet-like processes are found and we discuss their origin.

Notes: Abstract. We discuss the enumeration of Feynman diagrams at tree order for processes with external lines of different types. We show how this can be done by iterating algebraic Schwinger–Dyson equations. Asymptotic estimates for very many external lines are derived. Applications include QED, QCD and scalar QED, and the asymptotic estimates are numerically confronted with the exact results.

Notes: Abstract. Supersymmetric (SUSY) Ward identities are considered for the N=1 SU(2) SUSY Yang-Mills theory discretized on the lattice with Wilson fermions (gluinos). They are used in order to compute non-perturbatively a subtracted gluino mass and the mixing coefficient of the SUSY current. The computations were performed at gauge coupling $\beta=2.3$ and hopping parameter $\kappa\!=\!0.1925$ , 0.194, 0.1955 using the two-step multi-bosonic dynamical-fermion algorithm. Our results are consistent with a scenario where the Ward identities are satisfied up to O(a) effects. The vanishing of the gluino mass occurs at a value of the hopping parameter which is not fully consistent with the estimate based on the chiral phase transition. This suggests that, although SUSY restoration appears to occur close to the continuum limit of the lattice theory, the results are still affected by significant systematic effects.

Notes: Abstract. In the framework of a gauge invariant continuous and non-perturbative regularization scheme based on the smearing of point-like interactions by means of cutoff functions, we show that the axial anomaly, though cutoff independent, depends on the shape of the cutoff functions. The standard value for the strength of the axial anomaly is recovered if we assume that the regularized gauge invariant axial current is in addition local.

Notes: Abstract. We show that the non-commutative Yang–Mills field forms an irreducible representation of the (undeformed) Lie algebra of rigid translations, rotations and dilatations. The non-commutative Yang–Mills action is invariant under combined conformal transformations of the Yang–Mills field and of the non-commutativity parameter $\theta$ . The Seiberg–Witten differential equation results from a covariant splitting of the combined conformal transformations and can be computed as the missing piece to complete a covariant conformal transformation to an invariance of the action.

Notes: Abstract. Two simple proofs are presented for the first order virial expansion of the self-energy of a particle moving through a medium, characterised by temperature and/or chemical potential(s). One is based on the virial expansion of the self-energy operator itself, while the other is based on the analysis of its Feynman diagrams in configuration space.

Notes: Abstract. Starting from the divergence pattern of perturbative quantum chromodynamics, we propose a novel, non-power series replacing the standard expansion in powers of the renormalized coupling constant a. The coefficients of the new expansion are calculable at each finite order from the Feynman diagrams, while the expansion functions, denoted as $W_n(a)$ , are defined by analytic continuation in the Borel complex plane. The infrared ambiguity of perturbation theory is manifest in the prescription dependence of the $W_n(a)$ . We prove that the functions $W_n(a)$ have branch points and essential singularities at the origin a=0 of the complex a plane and that their perturbative expansions in powers of a are divergent, while the expansion of the correlators in terms of the $W_n(a)$ set is convergent under quite loose conditions.

Notes: Abstract. We formulate and analyse a saturation model for the total $\gamma \gamma$ and $\gamma^* \gamma^*$ cross-sections and for the real photon structure function $F_2^{\gamma}(x,Q^2)$ . The model is based on a picture in which the $\gamma^* \gamma^*$ total cross-section for arbitrary photon virtualities is driven by the interaction of colour dipoles into which the virtual photons fluctuate. The cross-section describing this interaction is assumed to satisfy the saturation property with the saturation radius taken from the Golec-Biernat and Wüsthoff analysis of the $\gamma^*p$ interaction at HERA. The model is supplemented by the QPM and non-pomeron reggeon contributions. The model gives a very good description of the data on the $\gamma \gamma$ total cross-section, on the photon structure function $F_2^{\gamma}(x,Q^2)$ at lowx and on the $\gamma^* \gamma^*$ cross-section extracted from LEP double tagged events. The production of heavy flavours in $\gamma \gamma$ collisions is also studied. Predictions of the model for the very high energy range which will be probed at future linear colliders are given.

Notes: Abstract. A new set of supersymmetric benchmark scenarios has recently been proposed in the context of the constrained MSSM (CMSSM) with universal soft supersymmetry-breaking masses, taking into account the constraints from LEP, $b \rightarrow s \gamma$ and $g_\mu - 2$ . These points have previously been used to discuss the physics reaches of different accelerators. In this paper, we discuss the prospects for discovering supersymmetric dark matter in these scenarios. We consider direct detection through spin-independent and spin-dependent nuclear scattering, as well as indirect detection through relic annihilations to neutrinos, photons, and positrons. We find that several of the benchmark scenarios offer good prospects for direct detection via spin-independent nuclear scattering and indirect detection via muons produced by neutrinos from relic annihilations inside the Sun, and some models offer good prospects for detecting photons from relic annihilations in the galactic centre.

Notes: Abstract. We study permutation invariant oscillator algebras and their Fock space representations using three equivalent techniques, i.e. (i) a normally ordered expansion in creation and annihilation operators, (ii) the action of annihilation operators on monomial states in Fock space and (iii) Gram matrices of inner products in Fock space. We separately discuss permutation invariant algebras which possess hermitean number operators and permutation invariant algebras which possess non-hermitean number operators. The results of a general analysis are applied to the $S_M$ -extended Heisenberg algebra, underlying the M-body Calogero model. Particular attention is devoted to the analysis of Gram matrices for the Calogero model. We discuss their structure, eigenvalues and eigenstates. We obtain a general condition for positivity of eigenvalues, meaning that all norms of states in Fock space are positive if this condition is satisfied. We find a universal critical point at which the reduction of the physical degrees of freedom occurs. We construct dual operators, leading to the ordinary Heisenberg algebra of free Bose oscillators. From the Fock-space point of view, we briefly discuss the existence of a mapping from the Calogero oscillators to the free Bose oscillators and vice versa.

Notes: Abstract. We study the interface between Regge behavior and DGLAP evolution in a non-perturbative model for the nucleon structure function based on a multipole pomeron exchange. This model provides the input for a subsequent DGLAP evolution that we calculate numerically. The soft input and its evolution give a good fit to the experimental data in the whole available range of x and $Q^2$ .

Notes: Abstract. Recent investigations of electroweak radiative corrections have revealed the importance of higher order contributions in high energy processes, where the size of typical corrections can exceed those associated with QCD considerably. Beyond one loop, only universal (angular independent) corrections are known to all orders except for massless $e^+ e^- \rightarrow f {\overline f}$ processes, where also angle dependent corrections exist in the literature. In this paper we present general arguments for the consistent resummation of angle dependent subleading (SL) logarithmic corrections to all orders in the regime where all invariants are still large compared to the gauge boson masses. We discuss soft isospin correlations, fermion mass and gauge boson mass gap effects, the longitudinal and Higgs boson sector as well as mixing contributions including CKM effects for massive quarks. Two loop results for the right handed Standard Model are generalized in the context of the high energy effective theory based on the standard model Lagrangian in the symmetric basis with the appropriate matching conditions to include the soft QED regime. The result is expressed in exponentiated operator form in a CKM extended isospin space in the symmetric basis. Thus, a full electroweak SL treatment based on the infrared evolution equation method is formulated for arbitrary high energy processes at future colliders. Comparisons with known results are presented.

Notes: Abstract. The sample of hadronic Z decays collected by the Aleph detector at Lep in the years 1991-1995 is analysed in order to measure the forward-backward asymmetry in ${\mathrm{Z}} \to{\mathrm{b}} \bar{{\mathrm{b}}}$ and ${\mathrm{Z}} \to{\mathrm c} \bar{{\mathrm c}}$ events and the ${\mathrm{B}}^0{\mathrm{-}}\bar{\mathrm{B}}^0$ average mixing parameter $\bar \chi$ . Quark charges are tagged by the charges of electrons and muons produced in ${\mathrm{b}}$ and ${\mathrm c}$ semileptonic decays. Multivariate analyses are used to separate the event flavours and ${\mathrm{b}} \to \ell$ / ${\mathrm{b}} \to{\mathrm c} \to \ell$ processes. The ${\mathrm{b}}$ and ${\mathrm c}$ quark asymmetries are measured simultaneously; the average mixing parameter and the pole asymmetries are determined to be $\begin{eqnarray*} \bar \chi &=& 0.1196 \pm 0.0049 \;{\mathrm{(stat.)}} \;{}^{\displaystyle{+0.0043}}_{\displaystyle{-0.0050}} \;{\mathrm{(syst.)}}, {\mathrm{A}}^{0,{\mathrm{b}}}_{\mathrm{FB}} &=& 0.0998 \pm 0.0040 \;{\mathrm{(stat.)}} \; \pm 0.0017 \;{\mathrm{(syst.)}}, {\mathrm{A}}^{0,{\mathrm c}}_{\mathrm{FB}} &=& 0.0732 \pm 0.0053 \;{\mathrm{(stat.)}} \; \pm 0.0037 \;{\mathrm{(syst.)}}. \end{eqnarray*}$ These asymmetries, combined with the Aleph measurements of the ${\mathrm{b}}$ asymmetry using inclusive ${\mathrm{b}}$ hadron decays and of the ${\mathrm c}$ asymmetry using reconstructed ${\mathrm{D}}$ mesons, correspond to a value of the effective electroweak mixing angle of ${\mathrm{sin}}^2\theta^{\mathrm{eff}}_{\mathrm{W}} = 0.23188 \pm 0.00046$ .

Notes: Abstract. The ”Snowmass Points and Slopes” (SPS) are a set of benchmark points and parameter lines in the MSSM parameter space corresponding to different scenarios in the search for Supersymmetry at present and future experiments. This set of benchmarks was agreed upon at the 2001 ”Snowmass Workshop on the Future of Particle Physics” as a consensus based on different existing proposals.

Notes: Abstract. Supersymmetric 5D SU(5) grand unification is considered. SU(5) is broken down to $G_{\mathrm{{SM}}}=SU(3)\times SU(2)\times U(1)$ by the $Z_2\times Z_2'$ assignment of the bulk field(s). The matter fields are located at the fixed point(s). In the bulk, a Higgs multiplet $\bar 5_H$ (containing the bottom doublet $H_1$ ) and the SU(5) gauge multiplet are located. At one fixed point, $H_2$ (the top doublet) and the standard model matter multiplets are presented. Because of the difference of the locations of $H_1$ and $H_2$ , one can obtain a hierarchy between top and bottom Yukawa couplings. We also present a possible way to understand the s– $\mu$ mass puzzle in this framework of the split multiplet.

Notes: Abstract. Electron–positron annihilation into hadrons plus an energetic photon from initial state radiation allows the hadronic cross-section to be measured over a wide range of energies. The full next-to-leading order QED corrections for the cross-section for $e^+ e^-$ annihilation into a real tagged photon and a virtual photon converting into hadrons are calculated where the tagged photon is radiated off the initial electron or positron. This includes virtual and soft photon corrections to the process $e^+ e^- \rightarrow \gamma+\gamma^*$ and the emission of two real hard photons: $e^+ e^- \rightarrow \gamma+\gamma+\gamma^*$ . A Monte Carlo generator has been constructed, which incorporates these corrections and simulates the production of two charged pions or muons plus one or two photons. Predictions are presented for centre-of-mass energies between 1 and 10 GeV, corresponding to the energies of DA $\Phi$ NE, CLEO-C and B-meson factories.

Notes: Abstract. We calculate the next-to-leading corrections to the jet vertex which is relevant for the Mueller-Navelet-jets production in $p\bar{p}$ collisions and for the forward jet cross section in ep collisions. In this first part we present the results of the vertex for an incoming quark. Particular emphasis is given to the separation of the collinear divergent part and the central region of the produced gluon.

Notes: Abstract. The contribution of proton polarizability to hydrogen hyperfine splitting is evaluated on the basis of modern experimental and theoretical results on the proton polarized structure functions. The value of this correction is equal to 1.4 ppm.

Notes: Abstract. We calculate the leading and next-to-leading logarithmic resummed distribution for the jet broadening in deep inelastic scattering, as well as the power correction for both the distribution and mean value. A truncation of the answer at NLL accuracy, as is standard, leads to unphysical divergences. We discuss their origin and show how the problem can be resolved. We then examine DIS specific procedures for matching to fixed order calculations and compare our results to the data. One of the tools developed for the comparison is an NLO parton distribution evolution code. When compared to PDF sets from MRST and CTEQ it reveals limited discrepancies in both.

Notes: Abstract. In this work, the mass of the strange quark is calculated from QCD sum rules for the divergence of the strangeness-changing vector current. The phenomenological scalar spectral function which enters the sum rule is determined from our previous work on strangeness-changing scalar form factors [1]. For the running strange mass in the $\bar{\rm MS}$ scheme, we find $m_s(2 {\mathrm{GeV}})=99\pm 16 {\mathrm{MeV}}$ . Making use of this result and the light quark mass ratios obtained from chiral perturbation theory, we are also able to extract the masses of the lighter quarks $m_u$ and $m_d$ . We then obtain $m_u(2 {\mathrm{GeV}})=2.9\pm 0.6 {\mathrm{MeV}}$ and $m_d(2 {\mathrm{GeV}})=5.2\pm 0.9 {\mathrm{MeV}}$ . In addition, we present an updated value for the light quark condensate.

Notes: Abstract. We investigate the mass differences $\Delta M_{B_{d,s}}$ in $B^0_{d,s}$ – $\bar B^0_{d,s}$ mixing with a new up-like quark $t^{\prime}$ in the sequential fourth generation model. We give the basic formulae for $\Delta M_{B_{d,s}}$ in this model and obtain two kinds of numerical results for $\Delta M_{B_{s}}$ as a function of $m_{t^{\prime}}$ . We find that one of our results can satisfy the present experimental lower bound of $\Delta M_{B_s}$ . We also get the constraints of the fourth generation CKM factor $V^*_{t'b}V_{t'd}$ , as a function of $t'$ , from the experimental measurements of $\Delta M_{B_d}$ . Thus, $\Delta M_{B_{d,s}}$ provides a possible test of the fourth generation and may give a signal of new physics.

Notes: Abstract. This paper describes the calculation of the semileptonic Kl3 decay form factors at order p6 of chiral perturbation theory, which is the next-to-leading order correction to the well-known p4 result achieved by Gasser and Leutwyler. At order p6 the chiral expansion contains one- and two-loop diagrams which are discussed in detail. The irreducible two-loop graphs of the sunset topology are calculated numerically. In addition, the chiral Lagrangian ${\cal L}^{(6)}$ produces direct couplings with the W bosons. Due to these unknown couplings, one can always add linear terms in q2 to the predictions of the form factor f - (q 2 ). For the form factor f + (q 2 ), this ambiguity involves even quadratic terms. Making use of the fact that the pion electromagnetic form factor involves the same q4 counterterm, the q4 ambiguity can be resolved. Apart from the possibility of adding an arbitrary linear term in q2 our calculation shows that chiral perturbation theory converges very well in this application, as the ${\cal O}(p^{6})$ corrections are small. Comparing the predictions of chiral perturbation theory with the recent CPLEAR data, it is seen that the experimental form factor f + (q 2 ) is well described by a linear fit, but that the slope $ \lambda _{+}$ is smaller by about 2 standard deviations than the ${\cal O} (p^{4})$ prediction. The unavoidable q2 counterterm of the ${\cal O}(p^{6})$ corrections allows one to bring the predictions of chiral perturbation theory into perfect agreement with experiment.

Notes: Abstract. We present a solution of the solar neutrino deficit using three flavors of neutrinos and R-parity non-conserving supersymmetry. In this model, in vacuum, the $\nu_e$ is massless and unmixed, mass and mixing being restricted to the $\nu_\mu$ - $\nu_\tau$ sector only, which we choose in consistency with the requirements of the atmospheric neutrino anomaly. The flavor changing and flavor diagonal neutral currents present in the model and the three-flavor picture together produce an energy dependent resonance-induced $\nu_e$ - $\nu_\mu$ mixing in the sun. This mixing plays a key role in the new solution to the solar neutrino problem. The best fit to the solar neutrino rates and spectrum (1258-day SK and 241-day SNO data) requires a mass square difference of $\sim 10^{-5}$ eV2 in vacuum between the two lightest neutrinos. This solution cannot accommodate a significant day-night effect for solar neutrinos nor CP violation in terrestrial neutrino experiments.

Notes: Abstract. The analysing power of the reaction ${\rm n} {\rm p} \rightarrow {\rm p} {\rm p} \pi^{-}$ for neutron energies between threshold and 570 MeV has been determined using a transversely polarised neutron beam at PSI. The reaction has been studied in a kinematically complete measurement using a time-of-flight spectrometer with large acceptance. Analysing powers have been determined as a function of the c.m. pion angle in different regions of the proton-proton invariant mass. They are compared to other data from the reactions ${\rm n} {\rm p} \rightarrow {\rm p} {\rm p} \pi^{-}$ and ${{\rm p} {\rm p} \rightarrow {\rm p} {\rm p} \pi^{0}}$ . The np elastic scattering analysing power was determined as a by-product of the measurements.

Notes: Abstract. We generalize the worldline variational approach to field theory by introducing a trial action which allows for anisotropic terms to be induced by external 4-momenta of Green's functions. By solving the ensuing variational equations numerically we demonstrate that within the (quenched) scalar Wick-Cutkosky model considerable improvement can be achieved over results obtained previously with isotropic actions. In particular, the critical coupling associated with the instability of the model is lowered, in accordance with expectations from Baym's proof of the instability in the unquenched theory. The physical picture associated with a different quantum mechanical motion of the dressed particle along and perpendicular to its classical momentum is discussed. Indeed, we find that for large couplings the dressed particle is strongly distorted in the direction of its four-momentum. In addition, we obtain an exact relation between the renormalized coupling of the theory and the propagator. Along the way we introduce new and efficient methods to evaluate the averages needed in the variational approach and apply them to the calculation of the 2-point function.

Notes: Abstract. We analyze the higher-twist effects and the SU(3)-flavor symmetry breaking in the correlation functions used to calculate form factors of pseudoscalar mesons in the QCD light-cone sum rule approach. It is shown that the Ward identities for these correlation functions yield relations between twist-4 two- and three-particle distribution amplitudes. In addition to the relations already obtained from the QCD equations of motions, we have found a new one. With the help of these relations, the twist-4 contribution to the light-cone sum rule for the pion electromagnetic form factor is reduced to a very simple form. Simultaneously, we correct a sign error in an earlier calculation. The updated light-cone sum rule prediction for the pion form factor at intermediate momentum transfers is compared with the recent Jefferson Lab data. Furthermore, from the correlation functions with strange-quark currents the kaon electromagnetic form factor and the $K\to \pi$ weak transition form factors are predicted with $O(m_s)\char126O(m_K^2)$ accuracy.

Notes: Abstract. A simple model for nuclear structure functions in the region of small x and small and moderate Q2 is presented. It is a parameter-free extension, in the Glauber-Gribov approach to nuclear collisions, of a saturation model for the nucleon. A reasonable agreement with experimental data on the ratios of nuclear structure functions is obtained. Nuclear effects in the longitudinal-to-transverse cross section ratios are found to be small. Predictions of the model for values of x smaller than those available to present experiments are given. The unintegrated gluon distribution and the behaviour of the saturation scale which result from this model are shown and discussed.

Notes: Abstract. We use the constituent quark model (CQM) to describe CDF data on double parton cross section and HERA data on the $J / \Psi$ ratio cross section of elastic and inelastic diffractive productions. Our estimate shows that the radius of the constituent quark turns out to be rather small, $R^2_{quark} \approx 0.1$ GeV-2, in accordance with the assumption on which CQM is based.

Notes: Abstract. We discuss the measured partial width of the pseudoscalar charmonium state $\eta_c$ into two photons. Predictions from potential models are examined and compared with experimental values. On including radiative corrections, it is found that present measurements are compatible both with a QCD type potential and with a static Coulomb potential. The latter is then used to give an estimate on the $\eta_b$ decay into two photons. Results for $\etac$ are also compared with those from $J/\psi$ data through the NRQCD model.

Notes: Abstract. The ${W b \bar b}$ , ${Z b \bar b}$ and ${t \bar t b \bar b}$ production at LHC are irreducible backgrounds for the possible observability of the standard model and minimal supersymmetric standard model light Higgs boson in processes involving associated WH, ZH and $t \bar t H$ production followed by the $H \to b \bar b$ decay. The comparison presented in this paper uses the background estimates obtained with (a) the complete massive matrix element implemented in the AcerMC Monte Carlo generator and (b) the PYTHIA implementation of the inclusive W, Z, and $t \bar t$ production, followed by the parton showering mechanism. Both approaches lead to the production of the final state of interest but differ in the approximations used. The focal point of this study is the comparison of the two approaches when estimating the background contributions to the light Higgs boson searches at the LHC.

Notes: Abstract. We consider the thermal correlation functions of vector and axial-vector currents and evaluate corrections to the vector and axial-vector meson pole terms to one loop in chiral perturbation theory. As expected, the pole positions do not shift to leading order in temperature. But the residues decrease with temperature. We review briefly other methods in the literature to determine these pole parameters. We find our evaluation to disprove a result on the mixing of the correlation functions at finite temperature.

Notes: Abstract. The phase structure of hadrons and the quark-gluon plasma is investigated by two types of equation of state of the hadrons, namely the ideal hadron gas model and the compressible bag model. It is pointed out that, while the ideal gas model produces an unrealistic extra hadron phase, the compressible bag model gives the expected and reasonable phase diagram even if the rich hadron spectrum is taken into account.

Notes: Abstract. We summarize the possible processes which may be used to search for a Higgs boson, of mass in the range 114-130 GeV, at the LHC. We discuss, in detail, two processes with rapidity gaps: exclusive Higgs production with tagged outgoing protons and production by Weak Boson Fusion, in each case taking $H\to b \bar b$ as the signal. We make an extensive study of all possible $b \bar b$ backgrounds, and discuss the relevant experimental issues. We emphasize the special features of these signals, and of their background processes, and show that they could play an important role in identifying a light Higgs boson at the LHC.

Notes: Abstract. We give a simple model to explain the origin of fermion families and chirality through the use of a domain wall-anti-domain wall pair placed in a five dimensional space-time.

Notes: Abstract. We present the final results obtained by the MACRO experiment in the search for GUT magnetic monopoles in the penetrating cosmic radiation, for the range $4\times 10^{-5}〈 \beta 〈 1$ . Several searches with all the MACRO sub-detectors (i.e. scintillation counters, limited streamer tubes and nuclear track detectors) were performed, both in stand alone and combined ways. No candidates were detected and a 90% Confidence Level (C.L.) upper limit to the local magnetic monopole flux was set at the level of $1.4\times 10^{-16}$ cm-2 s-1 sr-1. This result is the first experimental limit obtained in direct searches which is well below the Parker bound in the whole $\beta$ range in which GUT magnetic monopoles are expected.

Notes: Abstract. We study the differential branching ratio, the branching ratio and the forward-backward asymmetry for exclusive $B_s \to \phi \ell^+ \ell^+$ decay in the two Higgs doublet model. We analyze the dependences of these quantities on the model parameters and show that these observables are highly sensitive to new physics and hence may provide a powerful probe of the SM and beyond.

Notes: Abstract. The process of baryon number transfer due to string junction propagation in rapidity space is analyzed. It has a significant effect on the net baryon production in pp collisions at mid-rapidities and an even larger effect in the forward hemisphere in the cases of $\pi p$ and $\gamma p$ interactions. The results of numerical calculations in the framework of the quark-gluon string model are in reasonable agreement with the data.

Notes: Abstract. In this article we present the complete massless and massive one-loop triangle diagram results using the negative dimensional integration method (NDIM). We consider the following cases: massless internal fields; one massive, two massive with the same mass m and three equal masses for the virtual particles. Our results are given in terms of hypergeometric and hypergeometric-type functions of the external momenta (and masses for the massive cases) where the propagators in the Feynman integrals are raised to arbitrary exponents and the dimension of the space-time is D. Our approach reproduces the known results; it produces other solutions as yet unknown in the literature as well. These new solutions occur naturally in the context of NDIM revealing a promising technique to solve Feynman integrals in quantum field theories.

Notes: Abstract. Theoretical predictions for the polarized nucleon structure function g 1 (x, Q 2 ) at low Q2 are obtained in the framework of the generalized vector meson dominance model. Contributions from both light and heavy vector mesons are evaluated. In the photoproduction limit the first moment of g1 is related to the static properties of the nucleon via the Drell-Hearn-Gerasimov-Hosoda-Yamamoto sum rule. This property is employed to fix the magnitude of the light vector meson contribution to g1, using the recent measurements in the region of baryonic resonances. The results are compared to the data on g 1 (x, Q 2 ). Finally, the DHGHY moment function I(Q 2 ) is calculated, and our theoretical predictions are confronted with the recent preliminary data obtained at the Jefferson Laboratory.

Notes: Abstract. We study potential signals of neutralino dark matter indirect detection by neutrino telescopes in a wide range of CMSSM parameters. We also compare with direct detection potential signals taking into account in both cases present and future experiment sensitivities. Only models with neutralino annihilation into gauge bosons can satisfy cosmological constraints and current neutrino indirect detection sensitivities. For both direct and indirect detection, only next generation experiments will be able to really test this kind of models.

Notes: Abstract. We investigate the ground-state energy of the $\pi^-p$ atom (pionic hydrogen) in the framework of QCD + QED. In particular, we evaluate the strong energy-level shift. We perform the calculation at next-to-leading order in the low-energy expansion in the framework of the relevant effective field theory. The result provides a relation between the strong energy shift and the pion-nucleon S-wave scattering lengths - evaluated in pure QCD - at next-to-leading order in isospin-breaking and in the low-energy expansion. We compare our result with available model calculations.

Notes: Abstract. In this paper we consider the worldsheet of the superstring as a non-commutative space. Some additional terms can be added to the superstring action, such that for an ordinary worldsheet they are zero. The expansion of this extended action up to the first order of the non-commutativity parameter leads to the new supersymmetric action for the string. For the closed superstring, we obtain the boundary state that describes a brane. From the open string point of view, the new boundary conditions on the worldsheet bosons generalize the non-commutativity of spacetime. Finally, we suggest some definitions for the non-commutativity parameter of the superstring worldsheet.

Notes: Abstract. We revisit the decoupling phenomenon of massless modes in non-commutative open string (NCOS) theories. We check the decoupling by explicit computation in (2+1) or higher dimensional NCOS theories and recapitulate the validity of the decoupling to all orders in perturbation theory.

Notes: Abstract. The uncertainties due to limited knowledge of the multi-hadron final state on the measurements of the top mass at future linear colliders are discussed. This study is performed for $e^+e^-\to t\bar{t}$ annihilation events at the center-of-mass energy of s 1/2 =500 GeV using Monte Carlo models tuned to LEP experiments. The uncertainties are determined for the all-hadronic top-decay mode as well as for the lepton-plus-jets channel.

Notes: Abstract. We study the photoproduction of large $p_{\mathrm {T}}$ charged hadrons in e p collisions, both for the inclusive case and for the case where a jet in the final state is also measured. Our results are obtained by a NLO generator of partonic events. We discuss the sensitivity of the cross section to the renormalisation and factorisation scales, and to various fragmentation function parametrisations. The possibility to constrain the parton densities in the proton and in the photon is assessed. Comparisons are made with H1 data for inclusive charged hadron production.

Notes: Abstract. We discuss several mechanisms of heavy quark production in (real) photon-nucleon and (real) photon-(real) photon collisions. In particular we focus on the application of the saturation model. We discuss how to generalize the formula from virtual photon-proton scattering and analyze threshold effects. We discuss a possibility to measure the cross section for $\gamma \gamma \rightarrow 2 c 2 \bar c$ . In addition to the main dipole-dipole contribution included in a recent analysis, we propose how to calculate within the same formalism the hadronic single-resolved contribution to heavy quark production. At high energies this yields a sizable correction of about 30-40% for inclusive charm production and 15-20% for bottom production. We consider a subasymptotic component to the dipole-dipole approach. We get a good description of the recently measured $\sigma(\gamma \gamma \rightarrow c \bar c X)$ . Adding all possible contributions to $e^+ e^- \rightarrow b \bar b X$ together removes a huge deficit observed in earlier works but does not solve the problem totally. Whenever possible, we compare the present approach to the standard collinear one. We propose how to distinguish different mechanisms by measuring heavy quark-antiquark correlations.

Notes: Abstract. The interaction of a Grand Unification Magnetic Monopole with a nucleon can lead to a barion-number violating process in which the nucleon decays into a lepton and one or more mesons (catalysis of nucleon decay). In this paper we report an experimental study of the effects of a catalysis process in the MACRO detector. Using a dedicated analysis we obtain new magnetic monopole (MM) flux upper limits at the level of $\char1263\cdot 10^{-16} cm^{-2} s^{-1} sr^{-1}$ for $1.1\cdot 10^{-4} \le \vert\beta\vert \le 5\cdot 10^{-3}$ , based on the search for catalysis events in the MACRO data. We also analyze the dependence of the MM flux limit on the catalysis cross section.

Notes: Abstract. The complementarity between chiral perturbation theory and the linear sigma model is exploited to study $\pi^0\pi^0$ production in $\phi$ radiative decays, where the effects of the f 0 (980) scalar resonance, and those of its more controversial $\sigma (500)$ partner, should become manifest via the $\phi\rightarrow K^+ K^- (\gamma)\rightarrow\pi^0\pi^0\gamma $ decay chain. The recently reported data on $\phi\rightarrow\pi^0\pi^0\gamma$ coming from the VEPP-2M e + e - collider in Novosibirsk and the DA $\Phi$ NE $\phi$ -factory in Frascati can be reasonably described in our approach, which we propose as a promising first step towards more detailed analyses. The f 0 (980) contribution, which appears as a moderately narrow peak at the high part of the dipion mass spectrum, can be interpreted as the isoscalar member of the scalar nonet with a large $f_0 K\bar{K}$ coupling and an $f_0\pi\pi$ coupling suppressed by almost ideal $\sigma$ -f0 mixing. Indeed, the mixing angle in the flavor basis is found to be $\phi_{S}\approx - 6^\circ$ , if the f0 propagator is approximated by a simple Breit-Wigner expression, or $\phi_{S}\approx -9^\circ$ , if an improved two-channel analysis is performed. The $\sigma (500)$ resonance, which is then strongly coupled to pion pairs, yields a tiny contribution because, in our approach, its coupling to kaon pairs is proportional to $m^2_\sigma-m^2_K$ and thus quite small.

Notes: Abstract. We study Pomeron-Odderon interference effects giving rise to charge and single-spin asymmetries in diffractive electroproduction of a $\pi^+ \pi^-$ pair. We calculate these asymmetries, originating from both longitudinal and transverse polarizations of the virtual photon, in the framework of QCD and in the Born approximation, in a kinematical domain accessible to HERA experiments. We predict a sizable charge asymmetry with a characteristic dependence on the invariant mass of the $\pi^+ \pi^-$ pair, which makes this observable very important for establishing the magnitude of the Odderon exchange in hard processes. The single-spin asymmetry turns out to be rather small. We briefly discuss future improvements of our calculations and their possible effects on the results.

Notes: Abstract. We study the implications of the recently improved upper limits on the branching ratios for the decays $B \to \rho \gamma$ , expressed as $R(\rho \gamma/K^* \gamma)\equiv {\cal B}(B \to \rho \gamma)/{\cal B}(B \to K^* \gamma) \le 0.047$ . We work out the constraints that the current bound on $R(\rho \gamma/K^* \gamma)$ implies on the parameters of the quark mixing matrix in the standard model (SM). Using the present profile of the unitarity triangle, we predict this ratio to lie in the range $0.010 \leq R(\rho\gamma/K^*\gamma) \leq 0.046$ (at 95% C.L.), with the central value $R(\rho\gamma/K^*\gamma)=0.023$ . We also work out the correlations involving $R(\rho \gamma/K^* \gamma)$ , the isospin-violating ratio $\Delta (\rho \gamma)$ , and the direct CP-violating asymmetry $A_{CP}(\rho \gamma)$ in $B \to \rho \gamma$ decays in the SM, in the minimal supersymmetric extension of the SM (MSSM), and in an extension of the MSSM involving an additional flavor-changing structure in $b \to d$ transitions.

Notes: Abstract. The motion of a particle on the conical surface interacting with a scalar and a vector potential is studied in the path integral framework following the technique of constraints. The propagators are evaluated taking into account the problem of the angle periodicity. The result is given in a compact form.

Notes: Abstract. Diffractive heavy vector meson photoproduction accompanied by proton dissociation is studied for arbitrary momentum transfer. The process is described by the non-forward BFKL equation, for which a complete analytical solution is found, giving the scattering amplitude. The impact of non-leading corrections to the BFKL equation is also analysed. Results are compared to the HERA data on $J/\psi$ production.

Notes: Abstract. Two degenerate flavors of quarks are simulated with small masses down to about one fifth of the strange quark mass by using the two-step multi-boson (TSMB) algorithm. The lattice size is $8^3 \times 16$ with lattice spacing about $a \simeq 0.27 {\mathrm {fm}}$ which is not far from the N t =4 thermodynamical cross-over line. Autocorrelations of different physical quantities are estimated as a function of the quark mass. The eigenvalue spectra of the Wilson-Dirac operator are investigated.

Notes: Abstract. A model based on a dipole pomeron framework for exclusive vector meson photoproduction by real and virtual photons shows very good agreement with the experimental data. This model does not violate unitarity constraints and describes in a universal manner all the available data for $\rho$ , $\omega$ , $\varphi$ , $J/\psi$ and $\Upsilon$ vector meson photoproduction in the region of energies $1.7\le W \le 250{\mathrm { GeV}}$ and photon virtualities $0 \le Q^2 \le 35{\mathrm { GeV}}^2$ .

Notes: Abstract. A critical comparison is made between recent predictions of the cross sections for diffractive Higgs production at the Tevatron and the LHC. We show that the huge spread of the predictions arises either because different diffractive processes are studied or because important effects are overlooked. Exclusive production offers a reliable, viable Higgs signal at the LHC provided that proton taggers are installed.

Notes: Abstract. The problem of a relativistic spinning particle interacting with a quantized electromagnetic plane wave is treated by employing path integral methods and introducing the notion of a coherent state action. The dynamics of the particle spin is described using the supersymmetric action proposed recently by Alexandrou et al. in the so-called global representation. It is shown that to obtain the relative causal Green function, two fermionic identities, related directly to the classical equations of motion, have to be incorporated. The Green function, as constructed, allows us to extract in a natural way the expressions of the corresponding energy spectrum and wave functions.

Notes: Abstract. We focus on two aspects of CPT invariance in neutral meson-antimeson ( $M^0 \bar M^0$ ) mixing: (1) tests of CPT invariance, using only the property of ”lack of vacuum regeneration”, which occurs as a part of the well-known Lee-Oehme-Yang (LOY) theory; (2) methods for extracting the CPT-violating mixing parameter $\theta$ through explicit calculations by fully using the LOY-type theory. In the latter context, we demonstrate the importance of the C-even $\vert M^0 \bar M^0 \rangle$ state. In particular, by measuring the time dependence of opposite-sign dilepton events arising from decays of the C-even and C-odd $\vert M^0 \bar M^0 \rangle$ states, $\theta$ may be disentangled from the parameters $\lambda_+$ and $\bar \lambda_-$ characterizing violations of the $\Delta F = \Delta Q$ rule. Furthermore, these two parameters may also be determined. The same is true if one uses like-sign dilepton events arising from only the C-even $\vert M^0 \bar M^0 \rangle$ state.

Notes: Abstract. We compare distributions of leptons produced in hadronic collisions, by a horizontal neutral gauge boson, $Z^{\prime},$ suggested by the $Sp(6)_{\mathrm{L}}\otimes U(1)_{Y}$ model, to those produced by other theoretically motivated neutral gauge bosons occurring in left–right symmetric models and in superstring-inspired $E_6$ models. Forward–backward asymmetries in the gauge boson leptonic decay are found to be sensitive to specific forms of the couplings. The asymmetries are expected to be maximal for $Z^{\prime},$ distinguishing it from the other Z's.

Notes: Abstract. In this paper we extend the calculation of the QED corrections to deep inelastic lepton-proton scattering with a tagged photon, taking into account the full corrections on the lepton side. Comparing to previous results that were obtained by considering only large logarithmic terms at leading and next-to-leading accuray, we find that the difference is in general quite small, however, it may be significant in the region of large y and small x.

Notes: Abstract. The photon flux produced by light sources uniformly distributed in an infinite homogeneous medium is calculated on the basis of a known property of light propagation, taking into account the contribution of both absorption and scattering processes. The results are applied to the issue of the decays of $^{40}$ K content in sea salt and then to the rates detected by photomultipliers deployed in the deep sea. Numerical calculations are in agreement with the recent measurements performed in the Mediterranean Sea by the ANTARES and NEMO Collaborations.