Generation of gravitational waves in dynamical Chern-Simons gravity

TL;DR

This paper explores how a two-field inflationary model with a dynamical Chern-Simons term can produce amplified primordial gravitational waves detectable by future observatories, due to resonant effects and instabilities.

Contribution

It introduces a novel two-field inflationary framework with a dynamical Chern-Simons coupling that leads to distinctive GW signatures from resonant amplification and instabilities.

Findings

Primordial GWs are resonantly amplified in certain modes.

Isocurvature perturbations cause a tachyonic instability.

Resulting GWs are detectable by SKA, LISA, and Taiji.

Abstract

We investigate gravitational waves (GWs) generated in a two-field inflationary model with a non-canonical kinetic term, in which the gravitational Chern-Simons term is coupled to a heavy dynamical field. In such a model, primordial GWs experience a period of resonant amplification for some modes. In addition, isocurvature perturbations suffer from a temporary tachyonic instability due to an effective negative mass, which source curvature perturbations, resulting in large induced GWs. These two stochastic gravitational wave backgrounds correspond to different frequency bands, which are expected to be detected by future GW detectors such as SKA, LISA and Taiji.