Inflation and primordial gravitational waves in scale-invariant quadratic gravity with Higgs

TL;DR

This paper explores inflation in scale-invariant quadratic gravity, analyzing scalar and tensor perturbations, constraining model parameters with current data, and predicting potential detectability of gravitational waves by future CMB experiments.

Contribution

It introduces a novel inflationary model within scale-invariant quadratic gravity and provides detailed predictions for spectral indices and gravitational wave spectra.

Findings

Certain parameter regions are within reach of future CMB missions.

The model's spectral indices are consistent with current observational constraints.

Predicted gravitational wave signals could be detectable by upcoming experiments.

Abstract

In scale-invariant models of fundamental physics all mass scales are generated via spontaneous symmetry breaking. In this work, we study inflation in scale-invariant quadratic gravity, in which the Planck mass is generated classically by a scalar field, which evolves from an unstable fixed point to a stable one thus breaking scale-invariance. We investigate the dynamics by means of dynamical system standard techniques. By computing the spectral indices and comparing them with data, we put some constraints on the three dimensionless parameters of the theory. We show that certain regions of the parameter space will be within the range of future CMB missions like CMB-S4, LiteBIRD and STPol. The second half of the paper is dedicated to the analysis of inflationary first-order tensor perturbations and the calculation of the power spectrum of the gravitational waves. We comment on our results and compare them with the ones of mixed Starobinsky-Higgs inflation.