Oscillations and parity violation in gravitational wave background from extra tensor modes

TL;DR

This paper predicts that extra tensor modes from spectator fields can cause oscillations and parity-violating signatures in the gravitational wave background, which are detectable with future GW observatories.

Contribution

It introduces a universal prediction of oscillatory features and parity violation in GW spectra due to extra tensor modes using an effective field theory approach.

Findings

Oscillatory features in GW spectrum due to metric and tensor mode mixing

Chiral signatures from parity-violating operators in spin-2 sector

Potential detectability of these signatures with future GW detectors

Abstract

Spectator fields which provide additional tensor degrees of freedom, on top of the standard metric tensor perturbations, can produce significant amounts of gravitational waves (GWs). Employing the effective field theory approach for spin-2 fields, we find a universal prediction that linear mixing between the metric and extra tensor modes inevitably induces oscillatory features in the GW spectrum, reminiscent of the so-called neutrino oscillation. Moreover, parity-violating operators in the spin-2 sector can imprint chiral signatures on the resulting GW background. We consider a concrete scenario in which the spin-2 field generates observable chiral GWs with characteristic oscillatory patterns. These results provide a model-independent characterization of the key signatures and observational implications of such scenarios which can be detected with future GW detectors.