Scale-invariant cosmological perturbations from Horava-Lifshitz gravity without inflation

TL;DR

This paper proposes a scale-invariant cosmological perturbation generation mechanism within Horava-Lifshitz gravity, avoiding the need for inflation by leveraging anisotropic scaling and the curvaton mechanism.

Contribution

It introduces a novel scenario for generating scale-invariant perturbations using Horava-Lifshitz gravity without inflation or additional assumptions.

Findings

Quantum fluctuations are insensitive to Hubble rate due to anisotropic scaling.

The scenario works for power-law expansion with p>1/3.

It does not rely on the detailed balance condition.

Abstract

Based on the renormalizable theory of gravitation recently proposed by Horava, we present a simple scenario to generate almost scale-invariant, super-horizon curvature perturbations. The anisotropic scaling with dynamical critical exponent z=3 implies that the amplitude of quantum fluctuations of a free scalar field generated in the early epoch of the expanding universe is insensitive to the Hubble expansion rate and, thus, scale-invariant. Those fluctuations are later converted to curvature perturbations by the curvaton mechanism or/and the modulated decay of heavy particles/oscillating fields. This scenario works, for example, for power law expansion a\propto t^p with p>1/3 and, thus, does not require inflation. Also, this scenario does not rely on any additional assumptions such as the detailed balance condition.