Inflation and reheating in theories with spontaneous scale invariance symmetry breaking

TL;DR

This paper explores a scale-invariant quadratic gravity model with a scalar field, demonstrating spontaneous symmetry breaking, inflationary expansion, and potential reheating mechanisms consistent with observations.

Contribution

It presents a novel analysis of cosmological solutions in a scale-invariant quadratic gravity model, detailing how symmetry breaking leads to inflation and subsequent reheating.

Findings

Scale invariance is spontaneously broken, generating a mass scale.

The model predicts inflationary dynamics similar to Starobinsky's model.

Reheating can occur through oscillations around a stable fixed point.

Abstract

We study a scale-invariant model of quadratic gravity with a non-minimally coupled scalar field. We focus on cosmological solutions and find that scale invariance is spontaneously broken and a mass scale naturally emerges. Before the symmetry breaking, the Universe undergoes an inflationary expansion with nearly the same observational predictions of Starobinsky's model. At the end of inflation, the Hubble parameter and the scalar field converge to a stable fixed point through damped oscillations and the usual Einstein-Hilbert action is recovered. The oscillations around the fixed point can reheat the Universe in various ways and we study in detail some of these possibilities.