Probing cosmological fields with gravitational wave oscillations

TL;DR

This paper develops a framework to study gravitational wave oscillations caused by additional tensor modes from new fields or symmetries, predicting observable effects like waveform modulations and anomalous GW speeds.

Contribution

It introduces a general cosmological model for tensor mode oscillations and analyzes their phenomenology, including potential observational signatures.

Findings

Oscillations lead to waveform modulations

GW luminosity distance exhibits oscillations

Possible detection with current and future GW observatories

Abstract

Gravitational wave (GW) oscillations occur whenever there are additional tensor modes interacting with the perturbations of the metric coupled to matter. These extra modes can arise from new spin-2 fields (as in e.g. bigravity theories) or from non-trivial realisations of the cosmological principle induced by background vector fields with internal symmetries (e.g. Yang-Mills, gaugids or multi-Proca). We develop a general cosmological framework to study such novel features due to oscillations. The evolution of the two tensor modes is described by a linear system of coupled second order differential equations exhibiting friction, velocity, chirality and mass mixing. We follow appropriate schemes to obtain approximate solutions for the evolution of both modes and show the corresponding phenomenology for different mixings. Observational signatures include modulations of the wave-form, oscillations of the GW luminosity distance, anomalous GW speed and chirality. We discuss the prospects of observing these effects with present and future GW observatories such as LIGO/VIRGO and LISA.