Bouncing Galileon Cosmologies

TL;DR

This paper explores nonsingular bouncing cosmologies within the conformal Galileon model, analyzing perturbations and proposing a coupling to produce a scale-invariant spectrum consistent with observations.

Contribution

It introduces a novel bouncing solution in the Galileon framework and demonstrates how to generate a scale-invariant power spectrum through specific scalar couplings.

Findings

Nonsingular bouncing solutions start with radiation-dominated contraction.

Perturbations evolve smoothly with a blue-tilted spectrum.

A light scalar coupling can produce a scale-invariant spectrum.

Abstract

We present nonsingular, homogeneous and isotropic bouncing solutions of the conformal Galileon model. We show that such solutions necessarily begin with a radiation-dominated contracting phase. This is followed by a quintom scenario in which the background equation of state crosses the cosmological constant boundary allowing for a nonsingular bounce which in turn is followed by Galilean Genesis. We analyze the spectrum of cosmological perturbations in this background. Our results show that the fluctuations evolve smoothly and without any pathology, but the adiabatic modes form a blue tilted spectrum. In order to achieve a scale-invariant primordial power spectrum as required by current observations, we introduce a light scalar field coupling to the Galileon kinetically. We find two couplings which yield a scale-invariant spectrum, one of which requires a fine tuning of the initial conditions. This model also predicts a blue tilted spectrum of gravitational waves stemming from quantum vacuum fluctuations in the contracting phase.