Resonance instability of primordial gravitational waves during inflation in Chern-Simons gravity

TL;DR

This paper explores how Chern-Simons gravity during axion inflation causes resonance amplification of gravitational waves with polarization-dependent effects, leading to distinctive spectral features that differ from standard matter-induced backgrounds.

Contribution

It introduces a model where gravitational Chern-Simons coupling causes polarization-dependent resonance amplification of primordial gravitational waves during inflation.

Findings

Polarization-dependent amplification of tensor perturbations

Distinct spectral features such as peaks or plateaus

Characteristic infrared cutoff in gravitational wave spectrum

Abstract

We investigate axion inflation where the gravitational Chern-Simons term is coupled to a periodic function of the inflaton. We find that tensor perturbations with different polarizations are amplified in different ways by the Chern-Simons coupling. Depending on the model parameters, the resonance amplification results in a parity-violating peak or a board plateau in the energy spectrum of gravitational waves, and the sharp cutoff in the infrared region constitutes a characteristic distinguishable from stochastic gravitational wave backgrounds produced by matter fields in Einstein gravity.