Twisted echoes of an odd quartet: Scalar-induced gravitational waves as a probe of primordial parity-violation

TL;DR

This paper demonstrates how parity-violation in primordial scalar trispectra can produce detectable chiral gravitational waves, providing a new way to probe parity-violation in the early universe.

Contribution

It introduces the concept that scalar-induced gravitational waves can reveal parity-violation through their chirality, offering a novel observational probe.

Findings

Parity-odd trispectra induce detectable chiral gravitational waves.

SIGW can directly measure parity-violation in primordial non-Gaussianity.

Results suggest SIGW and parity-odd trispectra are complementary in testing parity-violating theories.

Abstract

Parity-violation leaves tell-tale trails in many cosmological observables. We illustrate parity-odd primordial scalar trispectra, that despite being of modest strength, impart detectable chirality to scalar-induced gravitational waves (SIGW). This allows us to impose strong bounds on the parity-odd part of trispectrum. Over certain scales, we find SIGW directly quantify parity-violation in primordial non-Gaussianity, unobscured by the Gaussian contribution. Our results call for treatment of SIGW and parity-odd trispectrum as complementary predictions of parity-violating theories.