The phase portrait of a matter bounce in Horava-Lifshitz cosmology

TL;DR

This paper analyzes the phase space of Horava-Lifshitz cosmology models to determine the conditions under which a cosmological bounce can occur, revealing that bounces are possible but not common, and identifying new oscillating universe solutions.

Contribution

It provides a phase space analysis of Horava-Lifshitz cosmology models, identifying conditions for bounces and discovering new oscillating universe solutions.

Findings

Bounces are possible but not generic in the models studied.

New bouncing solutions are identified beyond previously known ones.

Oscillating universe solutions are also found.

Abstract

The occurrence of a bounce in FRW cosmology requires modifications of general relativity. An example of such a modification is the recently proposed Horava-Lifshitz theory of gravity, which includes a ``dark radiation'' term with a negative coefficient in the analog of the Friedmann equation. This paper describes a phase space analysis of models of this sort with the aim of determining to what extent bouncing solutions can occur. A simplification, valid in the relevant region, allows a reduction of the dimension of phase space so that visualization in three dimensions is possible. It is found that a bounce is possible, but not generic in models under consideration. Apart from previously known bouncing solutions some new ones are also described. Other interesting solutions found include ones which describe a novel sort of oscillating universes.