Primordial Gravitational Waves in Parity-violating Symmetric Teleparallel Gravity

TL;DR

This paper explores how parity-violating extensions of symmetric teleparallel gravity influence inflationary gravitational waves, predicting detectable chiral signals with unique spectral features that could be observed by future space-based detectors.

Contribution

It introduces a novel application of PV symmetric teleparallel gravity to axion inflation, predicting distinctive chiral gravitational wave signatures and their potential detectability.

Findings

Primordial GWs exhibit a multi-peak energy spectrum with significant amplitude.

Chiral gravitational waves could be detected by LISA and Taiji.

Model parameters can be constrained using Fisher matrix analysis.

Abstract

In this paper, we investigate the inflationary phenomenology of parity-violating (PV) extensions of symmetric teleparallel gravity by applying this PV gravity theory to axion inflation. The presence of PV terms induces velocity birefringence in the tensor perturbations. During inflation, when the inflaton rapidly traverses the cliff-like region in its potential, the tensor modes at specific scales for one of the two circular polarization states undergo significant amplification due to tachyonic instability. Consequently, the resulting primordial gravitational waves (GWs), characterized by a one-handed polarization and a multi-peak structure in their energy spectrum, exhibit a significant amplitude potentially detectable by LISA and Taiji, and their chirality could be determined by the LISA-Taiji network. The detection of such a chiral GW signal provides an opportunity to probe inflation and PV gravity theory. Moreover, we perform the Fisher matrix analysis to forecast the constraints on the model parameters with the LISA-Taiji network.