Space-times admitting Penrose-Floyd tensors

We present the full integrability conditions for the Penrose-Floyd equation. Then we proceed to the integration of the Einstein equations under the assumption of the existence of a Penrose-Floyd tensor and we find all space-times admitting such a tensor.     

Wormholes with a barotropic equation of state admitting a one-parameter group of conformal motions

The theoretical construction of a traversable wormhole proposed by Morris and Thorne maintains complete control over the geometry by assigning both the shape and redshift functions, thereby leaving open the determination of the stress–energy tensor. This paper examines the effect of introducing the linear barotropic equation of state p_r=ωρ$p_r=\omega \rho$ on the theoretical construction. If either the energy density or the closely related shape function is known, then the Einstein field equations do not ordinarily yield a finite redshift function. If, however, the wormhole admits a one-parameter group of conformal motions, then both the redshift and shape functions exist provided that −3<ω<−1$-3<\omega <-1$. In a cosmological setting, the equation of state p=ωρ$p=\omega \rho$, ω<−1$\omega <-1$, is associated with phantom dark energy, which is known to support traversable wormholes. The restriction −3<ω<−1$-3<\omega <-1$ that arises in the present wormhole setting can be attributed to the assumption of conformal symmetry.     

Space-times containing perfect fluids and having a vanishing conformal divergence

The solutions of the Einstein field equations are studied under the assumptions that (1) the source of the gravitational field is a perfect fluid, (2) the divergence of the conformal (Weyl) tensor vanishes, and (3a) either an equation of state exists such thatp=p (w),p being the pressure andw the rest energy density, or (3b) the rest particle density is conserved. Under assumptions (1), (2), and (3a) it is shown that the space-time is conformally flat and the metric is a Robertson-Walker metric. The flow is irrotational, shear-free, and geodesic. Under assumptions (1), (2), and (3b) it is shown that either the line element is static or the fluid has a very special caloric equation of state. Conditions for a static solution to exist are examined, and it is shown that the Schwarzschild interior solution satisfies these conditions as does the Einstein universe. The Schwarzschild interior and the Einstein universe are the only conformally flat, static solutions obeying (1), (2), and (3b).The research reported herein was supported in part by the Atomic Energy Commission under contract number AT (11-1)-34, Project Agreement No. 125.     

Charged gravastars admitting conformal motion

We propose a new model of a gravastar admitting conformal motion. While retaining the framework of the Mazur-Mottola model, the gravastar is assumed to be internally charged, with an exterior defined by a Reissner-Nordström instead of a Schwarzschild line element. The solutions, obtained by exploiting an assumed conformal Killing vector, involve (i) the interior region, (ii) the shell, and (iii) the exterior region of the sphere. Of these three cases the first one is of primary interest since the total gravitational mass here turns out to be an electromagnetic mass under some specific conditions. This suggests that the interior de Sitter vacuum of a charged gravastar is essentially an electromagnetic mass model that must generate gravitational mass which provides a stable configuration by balancing the repulsive pressure arising from charge with its attractive gravity to avert a singularity. Therefore the present model, like the Mazur-Mottola model, results in the construction of a compact astrophysical object, as an alternative to a black hole. We have also analyzed various other aspects such as the stress energy tensor in the thin shell and the entropy of the system.     

Wormhole supported by dark energy admitting conformal motion

In this article, we study the possibility of sustaining static and spherically symmetric traversable wormhole geometries admitting conformal motion in Einstein gravity, which presents a more systematic approach to search a relation between matter and geometry. In wormhole physics, the presence of exotic matter is a fundamental ingredient and we show that this exotic source can be dark energy type which support the existence of wormhole spacetimes. In this work we model a wormhole supported by dark energy which admits conformal motion. We also discuss the possibility of the detection of wormholes in the outer regions of galactic halos by means of gravitational lensing. Studies of the total gravitational energy for the exotic matter inside a static wormhole configuration are also performed.     

Space-times with a stable adiabatic vacuum

The adiabatic particle definition of Parker [1] has found widespread acceptance (see, e.g., [2]) in the semiclassical approach to quantum gravity. We give sufficient conditions on a space-time so that, using the adiabatic particle definition, exactly zero particles are created; for these space-times the adiabatic vacuum is stable. The difficulties in formulating necessary conditions are discussed.This essay received an honorable mention from the Gravity Research Foundation for the year 1983-Ed.     

Topological defect solutions in the spherically symmetric space-time admitting conformal motion

In this paper, we have examined strings with monopole and electric field and domain walls with matter and electric field in the spherically symmetric space-time admitting a one-parameter group of conformal motions. For this purpose, we have solved Einstein's field equations for a spherically symmetric space-time via conformal motions. Also, we have discussed the features of the obtained solutions.     

On the rescaling problem of space-times admitting groups of conformal motions

The necessary and sufficient conditions are given that a space-time admitting a group of conformal motions can be mapped conformally on a space-time admitting the same group but of Killing symmetries.     

The fifteen-parameter conformal group

The space of lines in a Hermitean quadric of signature (2, 2) in complex projective three-space is a quadric of signature (2, 4) in real projective five-space, the conformal compactification of Minkowski space. This geometric fact leads to the classical isomorphism ofPSU(2, 2) and the identity component ofPO(2, 4; ), the 15-parameter conformal group. In this paper it is shown how the geometry and the isomorphism, for all components ofPO(2, 4; ), arise naturally from a real form of the Clifford algebra, and its associated spin groups, of a certain complex vector space determined by skew-symmetric 4×4 matrices and having their Pfaffian as quadratic form.     

Gauging the conformal group

It is demonstrated that Kibble’s method of gauging the Poincaré group can be applied to the gauging of the conformal group. The action of the gauge transformations is the action of general spacetime diffeomorphisms (or coordinate transformations) combined with a local action of an 11-parameter subgroup of SO(4,2). Because the translational subgroup is not an invariant subgroup of the conformal group the appropriate generalisation of the derivative of a physical field is not a covariant derivative in the usual sense, but this does not lead to any inconsistencies.     

Conformally Ricci-flat spacetimes admitting a Killing vector field parallel to the gradient of the conformal scalar field

It is shown that the stress-energy tensor of a conformally Ricci-flat spacetime in which there exists a Killing vector field parallel to the gradient of the conformal scalar field (a) cannot be of the perfect fluid type and (b) can only originate in an electromagnetic field when the latter is null and the solution belongs to a particular class of pp-waves.     

Faddeev-Jackiw quantization method in conformal three-dimensional supergravity

The conformal supergravity in three space-time dimensions is described by a pure Lorentz-Chern-Simons term. This system has constraints on curvatures and so it is a higher-derivative gauge model. The dynamical properties of this model are analyzed by means of the supersymmetric extension of the Faddeev-Jackiw symplectic quantization method. Using this algorithm in the first-order formalism, we study the gauge supersymmetric transformations and we find the constraints of the model.     

Representing functionally the two-dimensional conformal group

Projective representations of the two-dimensional conformal group are explicitly constructed in terms of propagation kernels. The representation functionals are then used to study the effect of conformal transformations on the states of a free massless scalar field theory.     

Conformal Geodesics on Vacuum Space-times

 A classification of discrete integrable systems on quad–graphs, i.e. on surface cell decompositions with quadrilateral faces, is given. The notion of integrability laid in the basis of the classification is the three–dimensional consistency. This property yields, among other features, the existence of the discrete zero curvature representation with a spectral parameter. For all integrable systems of the obtained exhaustive list, the so called three–leg forms are found. This establishes Lagrangian and symplectic structures for these systems, and the connection to discrete systems of the Toda type on arbitrary graphs. Generalizations of these ideas to the three–dimensional integrable systems and to the quantum context are also discussed. Received: 14 February 2002 / Accepted: 22 September 2002 Published online: 8 January 2003 Acknowledgements. This research was partly supported by DFG (Deutsche Forschungsgemeinschaft) in the frame of SFB 288 ``Differential Geometry and Quantum Physics'. V.A. was also supported by the RFBR grant 02-01-00144. He thanks TU Berlin for warm hospitality during the visit when part of this work has been fulfilled. Communicated by L. Takhtajan     

Space-times with spherically symmetric hypersurfaces

When discussing spherically symmetric gravitational fields one usually assumes that the whole space-time is invariant under theO(3) group of transformations. In this paper, the Einstein field equations are investigated under the weaker assumption that only the 3-spacest=const areO(3) symmetric. The following further assumptions are made: (1) Thet lines are orthogonal to the spacest=const. (2) The source in the field equations in a perfect fluid, or dust, or the term, or the empty space. (3) With respect to the center of symmetry the fluid source may move only radially if at all. Under these assumptions one solution with a perfect fluid source, found previously by Stephani, is recovered and interpreted geometrically, and it is shown that it is the sole solution which is not spherically symmetric in the traditional sense. The paper ends with a general discussion of cosmological models whose 3-spacest=const are the same as in the Robertson-Walker models. No new solutions were explicitly found, but it is shown that such models exist in which the sign of curvature is not fixed in time.     

Space-times carrying a quasirecurrent pairing of vector fields

A quasirecurrent pairing of vector fields {X₁, X₂} (defined in [1]) is investigated on a space-time in two cases: (1)X ₁ is spacelike andX ₂ is timelike; (2) X₁ is null andX ₂ space-like. The physical interpretation of these vector fields is given.     

Tensor Distributions on Signature-changing Space-times

Irregularities in the metric tensor of a signature-changing space-time suggest that field equations on such space-times might be regarded as distributional. We review the formalism of tensor distributions on differentiable manifolds, and examine to what extent rigorous meaning can be given to field equations in the presence of signature-change, in particular those involving covariant derivatives. We find that, for both continuous and discontinuous signature-change, covariant differentiation can be defined on a class of tensor distributions wide enough to be physically interesting.     

Space-times with covariant-constant energy-momentum tensor

It is shown that a general relativistic space-time with covariant-constant energy-momentum tensor is Ricci symmetric. Two particular types of such general relativistic space-times are considered and the nature of each is determined.     

Functional representation for the two-dimensional conformal group

A functional projective representation for the two-dimensional conformal group is explicitly constructed. The representation functionals are propagation kernels for self-dual fields.