Resolution of cosmological singularity in Ho\v{r}ava-Lifshitz cosmology

TL;DR

This paper reviews how Hořava-Lifshitz gravity modifies cosmological equations to potentially resolve the initial singularity through a universe bounce, analyzing stability and different formulations of the theory.

Contribution

It provides a comprehensive review of stability analyses and various formulations of Hořava-Lifshitz gravity addressing the cosmological singularity problem.

Findings

HL gravity enables a universe bounce replacing the singularity

Stability of the bounce depends on specific formulations of HL theory

Higher-order terms in HL theory influence cosmological evolution

Abstract

The standard $\Lambda$CDM model despite its agreement with observational data still has some issues unaddressed, lie the problem of initial singularity. Solving that problem usually requires modifications of general relativity. However, there appeared the Ho\v{r}ava-Lifshitz (HL) theory of gravity, in which equations governing cosmological evolution include a new term scaling similarly as dark radiation term in the Friedmann equations, enabling a bounce of the universe instead of initial singularity. This review describes past works on a stability of such a bounce in different formulations of HL theory, initial detailed balance scenario and further projectable versions containing higher than quadratic term to the original action.