Vector dark radiation and gravitational-wave polarization

TL;DR

This paper explores how conformal vector dark radiation affects gravitational wave propagation, leading to polarization effects and anisotropies in the tensor power spectrum, with potential observational implications.

Contribution

It introduces the impact of vector dark radiation on gravitational waves, revealing polarization and anisotropy effects not previously detailed in cosmological models.

Findings

Suppression of tensor transfer function at large scales.

Imprinting of anisotropies in the tensor power spectrum.

Induction of net polarization and polarization conversion in gravitational waves.

Abstract

We consider conformal vector models which could play the role of a cosmological dark radiation component. We analyse the propagation of gravitational waves in the presence of this vector background and find a suppression in the tensor transfer function at large scales. We also find that although the cosmological background metric is isotropic, anisotropies are imprinted in the tensor power spectrum. In addition, the presence of the background vector fields induces a net polarization of the gravitational wave background and, for certain configurations of the vector field, a linear to circular polarization conversion. We also show that this kind of effects are also present for vector models with more general potential terms.