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  • 1
    Electronic Resource
    Electronic Resource
    Special conformal Killing vector space-times and symmetry inheritance (1989)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 30 (1989), S. 2616-2625 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: Viscous heat-conducting fluid and anisotropic fluid space-times admitting a special conformal Killing vector (SCKV) are studied and some general theorems concerning the inheritance of the symmetry associated with the SCKV are proved. In particular, for viscous fluid space-times it is shown that (i) if the SCKV maps fluid flow lines into fluid flow lines, then all physical components of the energy-momentum tensor inherit the SCKV symmetry; or (ii) if the Lie derivative along a SCKV of the shear viscosity term ησab is zero then, again, we have symmetry inheritance. All space-times admitting a SCKV and satisfying the dominant energy condition are found. Apart from the vacuum pp-wave solutions, which are the only vacuum solutions that can admit a SCKV, the energy-momentum tensor associated with these space-times is shown to admit at least one null eigenvector and can represent either a viscous fluid with heat conduction or an anisotropic fluid. No perfect fluid space-times can admit a SCKV. These SCKV space-times and, also, space-times admitting a homothetic vector are used to illustrate the symmetry inheritance theorems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.528492
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  • 2
    Electronic Resource
    Electronic Resource
    Conformal symmetry inheritance with cosmological constant (1992)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 33 (1992), S. 4002-4007 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: A study is made of space-times satisfying the Einstein field equations with a nonzero cosmological constant and admitting a conformal Killing vector (CKV), ξa, which is such that the Lie derivative of the energy-momentum tensor in the direction of ξa is zero. This condition is necessary, but not sufficient, to ensure that the physical quantities associated with the energy-momentum tensor inherit the CKV symmetry. It is shown that this condition leads to two classes of space-times, each of which may be regarded as generalizations of the de Sitter space-times. The possible physical interpretations of these models are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.529850
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  • 3
    Electronic Resource
    Electronic Resource
    Space-times admitting special affine conformal vectors (1990)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 31 (1990), S. 649-652 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: Space-times admitting a special affine conformal vector (SACV) are shown to be precisely the space-times that admit a special conformal Killing vector. All possible SACV space-times are listed together with the corresponding SACV's and covariantly constant tensors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.528899
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  • 4
    Electronic Resource
    Electronic Resource
    Two-fluid cosmological models (1986)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 27 (1986), S. 406-416 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: Homogeneous and isotropic, relativistic two-fluid cosmological models are investigated. In these models two separate fluids act as the source of the gravitational field, as represented by the FRW line element. The general theory of two-fluid FRW models in which neither fluid need be comoving or perfect is developed. However, attention is focused on the physically interesting special class of flat FRW models in which one fluid is a comoving radiative perfect fluid and the second a noncomoving imperfect fluid. The first fluid is taken to model the cosmic microwave background and the second to model the observed material content of the universe. One of the motivations of the present work is to model the observed velocity of our galaxy relative to the cosmic microwave background that was recently discovered by G. F. Smoot, M. V. Gorenstein, and R. A. Muller [Phys. Rev. Lett. 39, 898 (1977)]. Several models within this special class are found and analyzed. The models obtained are theoretically satisfactory in that they are represented by solutions of Einstein's field equations and the laws of thermodynamics in which all the physical quantities occurring in the solutions are suitably well behaved. In addition, the models are in agreement with current observations. Consequently it is believed that the models obtained are physically acceptable models of the universe.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.527347
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  • 5
    Electronic Resource
    Electronic Resource
    Affine conformal vectors in space-time (1992)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 33 (1992), S. 1754-1764 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: All space-times admitting a proper affine conformal vector (ACV) are found. By using a theorem of Hall and da Costa, it is shown that such space-times either (i) admit a covariantly constant vector (timelike, spacelike, or null) and the ACV is the sum of a proper affine vector and a conformal Killing vector or (ii) the space-time is 2+2 decomposable, in which case it is shown that no ACV can exist (unless the space-time decomposes further). Furthermore, it is proved that all space-times admitting an ACV and a null covariantly constant vector (which are necessarily generalized pp-wave space-times) must have Ricci tensor of Segré type {2,(1,1)}. It follows that, among space-times admitting proper ACV, the Einstein static universe is the only perfect fluid space-time, there are no non-null Einstein–Maxwell space-times, and only the pp-wave space-times are representative of null Einstein–Maxwell solutions. Otherwise, the space-times can represent anisotropic fluids and viscous heat-conducting fluids, but only with restricted equations of state in each case.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.529652
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  • 6
    Electronic Resource
    Electronic Resource
    Conformally Ricci-flat viscous fluids (1990)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 31 (1990), S. 1704-1706 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: It is shown that if the gradient of the conformal scalar in a conformally Ricci-flat space-time is parallel to an eigenvector (timelike, spacelike, or null) of the stress-energy tensor, then acceptable solutions, without restrictions on the physical and kinematical quantities, of the Einstein field equations for a viscous fluid with heat conduction may be found.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.528718
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  • 7
    Electronic Resource
    Electronic Resource
    FRW Models as Exact Viscous Magnetohydrodynamical Cosmologies (1984)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 422 (1984), S. 0 
    Details
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1749-6632.1984.tb23372.x
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  • 8
    Electronic Resource
    Electronic Resource
    Observations and FRW Models (1986)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 470 (1986), S. 0 
    Details
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1749-6632.1986.tb47994.x
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  • 9
    Electronic Resource
    Electronic Resource
    A class of algebraically general solutions of the Einstein-Maxwell equations for non-null electromagnetic fields. II (1976)
    Springer
    General relativity and gravitation 7 (1976), S. 479-486 
    Details
    ISSN: 1572-9532
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In a previous article the Einstein-Maxwell field equations for non-null electromagnetic fields were studied under the conditions that the null tetrad is parallel-propagated along both principal null congruences. A solution with twist and shear, but no expansion, was found and was conjectured to be the only expansion-free solution. Here it is shown that this conjecture is false; the general expansion-free solution is found to be a family of space-times depending on a single constant parameter which is the ratio of the (constant) twists of the two principal null congruences.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00766405
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  • 10
    Electronic Resource
    Electronic Resource
    Common solutions of the einstein and Brans-Dicke theories (1974)
    Springer
    International journal of theoretical physics 11 (1974), S. 353-356 
    Details
    ISSN: 1572-9575
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract It is shown that non-trivial solutions common to the vacuum field equations of the Einstein and of the Brans-Dicke theories necessarily representpp-waves and the set of all common solutions is precisely the set of allpp-wave solutions of the Einstein equations. The form of the associated scalar field is found and is shown to be singular when ω〈−1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01808090
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