New Non-Separable Diagonal Cosmologies

TL;DR

This paper classifies new non-separable diagonal cosmological models with perfect fluids, exploring their physical properties, singularities, and relation to known cosmologies like FRW.

Contribution

It provides a complete classification of non-separable G2 diagonal perfect fluid cosmologies with constant quotient of Killing vector norms.

Findings

Four families of solutions depending on parameters

Analysis of energy conditions and singularities

Some solutions include FRW cosmologies as special cases

Abstract

We find all the perfect fluid G2 diagonal cosmologies with the property that the quotient of the norms of the two orthogonal Killing vectors is constant along each fluid world-line. We find four different families depending each one on two or three arbitrary parameters which satisfy that the metric coefficients are not separable functions. Some physical properties of these solutions including energy conditions, kinematical quantities, Petrov type, the existence and nature of the singularities and whether they contain Friedman-Robertson-Walker cosmologies as particular cases are also included.