Homothetic matter collineations of LRS Bianchi type V spacetimes with perfect fluid source

For a perfect fluid source, we have investigated the homothetic matter collineations (HMCs) of locally rotationally symmetric (LRS) Bianchi type V spacetimes. For degenerate energy–momentum tensor, two cases arise. In one case, the solution of HMC equations yields 11-dimensional algebra of HMCs while in the second case, we have infinite number of HMCs. When the energy–momentum tensor is non-degenerate, we have four cases, each giving five-dimensional algebra of HMCs. Some LRS Bianchi type V metrics are provided admitting HMCs.

Homothetic matter collineations of static plane symmetric spacetimes

In this paper, we present a complete classification of static plane symmetric spacetimes via their homothetic symmetries of the energy–momentum tensor, known as homothetic matter collineations (HMCs). The HMC equations for these spacetimes are derived and then solved by considering the degeneracy and non-degeneracy of the energy–momentum tensor. In the former case, we have obtained 6, 11 and infinite number of HMCs, while in the latter case, the solution of HMC equations yields 6-, 7-, 8-, 10- and 11-dimensional algebra of HMCs. The obtained HMCs generate some differential constraints involving the components of the energy–momentum tensor. Some examples of static plane symmetric spacetime metrics satisfying these constraints are provided and the physical interpretations of these metrics are discussed.

Homothetic matter collineations of LRS Bianchi type I spacetimes

A complete classification of locally rotationally symmetric (LRS) Bianchi type I spacetimes via homothetic matter collineations (HMCs) is presented. For non-degenerate energy–momentum tensor, a general form of the vector field generating HMCs is found, subject to some integrability conditions. Solving the integrability conditions in different cases, it is found that the LRS Bianchi type I spacetimes admit 6-, 7-, 8-, 10- or 11-dimensional Lie algebra of HMCs. When the energy–momentum tensor is degenerate, two cases give 6 and 11 HMCs, while the remaining cases produce infinite number of HMCs. Some LRS Bianchi type I metrics are provided admitting HMCs.

ON THE DEFINITION OF MATTER COLLINEATIONS

It is shown that when the stress–energy tensor of a spacetime is diagonal and is written in the mixed form, its collineations admit infinite dimensional Lie algebras except possibly in the case when the tensor depends on all the spacetime coordinates. The result can be extended for more general second rank tensors.

PROPER MATTER COLLINEATIONS OF PLANE SYMMETRIC SPACETIMES

We investigate matter collineations of plane symmetric spacetimes when the energy–momentum tensor is degenerate. There exists three interesting cases where the group of matter collineations is finite-dimensional. The matter collineations in these cases are either four, six or ten in which four are isometries and the rest are proper.

SYMMETRIES OF LOCALLY ROTATIONALLY SYMMETRIC MODELS

Matter collineations of locally rotationally symmetric space–times are considered. These are investigated when the energy–momentum tensor is degenerate. We know that the degenerate case provides infinite dimensional matter collineations in most of the cases. However, an interesting case arises where we obtain proper matter collineations. We also solve the constraint equations for a particular case to obtain some cosmological models.

MATTER COLLINEATIONS OF BIANCHI V SPACETIME

Matter collineations of the Bianchi V spacetime are studied according to degenerate or non-degenerate energy–momentum tensor. We have found that in degenerate case there are infinitely many matter collineations, whereas two cases give finite number of matter collineations which are five and six. When the energy–momentum tensor is non-degenerate, we obtain either four, five, six or seven independent matter collineations, out of which three are minimal Killing vectors and the rest are proper matter collineations.