Cosmological perturbations in a healthy extension of Horava gravity

TL;DR

This paper investigates scalar cosmological perturbations within a healthy extension of Horava gravity, demonstrating that large-scale evolution converges to a single curvature perturbation, simplifying the understanding of cosmological dynamics in this theory.

Contribution

It provides an analytical and numerical study of scalar modes in extended Horava gravity, showing improved behavior of the scalar mode and its impact on cosmological perturbations.

Findings

Large-scale perturbations converge to a single constant, ζ.

Evolution of perturbations is fully determined by ζ.

The extension addresses problems with the original Horava gravity scalar mode.

Abstract

In Horava's theory of gravity, Lorentz symmetry is broken in exchange for renormalizability, but the original theory has been argued to be plagued with problems associated with a new scalar mode stemming from the very breaking of Lorentz symmetry. Recently, Blas, Pujolas, and Sibiryakov have proposed a healthy extension of Horava gravity, in which the behavior of the scalar mode is improved. In this paper, we study scalar modes of cosmological perturbations in extended Horava gravity. The evolution of metric and density perturbations is addressed analytically and numerically. It is shown that for vanishing non-adiabatic pressure of matter the large scale evolution of cosmological perturbations converges to that described by a single constant, $\zeta$, which is an analog of a curvature perturbation on the uniform-density slicing commonly used in usual gravitational theories. The subsequent evolution is thus determined completely by the value of $\zeta$.