Testing parity symmetry of gravity with gravitational waves

TL;DR

This paper reviews how gravitational wave observations can test parity symmetry in gravity, focusing on parity-violating theories and their observable effects on GW polarization modes, with implications for current and future experiments.

Contribution

It summarizes recent progress in parity-violating gravity theories and discusses how GW data can constrain the energy scale of parity violation in gravity.

Findings

Current GW observations can set bounds on parity violation energy scales.

Parity-violating effects manifest as differences in polarization modes of GWs.

Future GW and CMB observations can further test parity symmetry at high energies.

Abstract

The examination of parity symmetry in gravitational interactions has drawn increasing attention. Although Einstein's General Relativity is parity-conserved, numerous theories of parity-violating (PV) gravity in different frameworks have recently been proposed for different motivations. In this review, we briefly summarize the recent progress of these theories, and focus on the observable effects of PV terms in the gravitational waves (GWs), which are mainly reflected in the difference between the left-hand and right-hand polarization modes. We are primarily concerned with the implications of these theories for GWs generated by the compact binary coalescences and the primordial GWs generated in the early Universe. The deviation of GW waveforms and/or primordial power spectrum can always be quantified by the energy scale of parity violation of the theory. Applying the current and future GW observation from laser interferometers and cosmic microwave background radiation, the current and potential constraints on the PV energy scales are presented, which indicates that the parity symmetry of gravity can be tested in high energy scale in this new era of gravitational waves.