Inflation in general covariant Ho\v{r}ava-Lifshitz gravity without projectability

TL;DR

This paper investigates inflation within a non-projectable, covariant Hořava-Lifshitz gravity framework, deriving perturbation equations, calculating power spectra, and showing consistency with observations, highlighting unique corrections from the theory's high-order derivatives.

Contribution

It provides the first derivation of the master equation for scalar perturbations in this specific gravity model without gauge fixing, demonstrating its compatibility with cosmological data.

Findings

Perturbations remain scale-invariant.

Corrections to standard power spectrum are due to high-order derivatives.

Perturbation equations are explicitly derived without gauge fixing.

Abstract

In this paper, we study inflation in the general covariant Ho\v{r}ava-Lifshitz gravity without the projectability condition. We write down explicitly the equations of the linear scalar perturbations of the FRW universe for a single scalar field without specifying to any gauge. Applying these equations to a particular gauge, we are able to obtain a master equation of the perturbations, in contrast to all the other versions of the theory without the projectability condition. This is because in the current version of the theory it has the same degree of freedom of general relativity. To calculate the power spectrum and index, we first define the initial conditions as the ones that minimize the energy of the ground state. Then, we obtain the full solutions of the equation of motion, by using the WKB approximations. From these solutions, we calculate the power spectrum and spectrum index of the comoving curvature perturbations and find the corrections due to the high order spatial derivative terms of the theory to those standard results obtained in general relativity. Remarkably, partly of corrections are a direct consequence of the non-projectability condition. It is also shown that the perturbations are still of scale-invariance, and the results obtained in the general covariant Ho\v{r}ava-Lifshitz gravity without the projectability condition are consistent with all current cosmological observations.