Vector dark radiation and gravitational-wave polarization

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.

Probing neutrino interactions and dark radiation with gravitational waves

“…We first review the well-established theory of the dynamics of gravitational and matter perturbations in the early Universe in application to the coupling of gravitational waves and relativistic species (of any spin). Gravitational waves also interact with other types of matter, including relativistic axions [90,91], nonrelativistic and collisional matter [92][93][94][95], and vector fields [96][97][98][99]; some of these scenarios are not captured by the kinetic theory treatment we review. We neglect any chemical potential that would be requisite to describe, e.g., chiral fermions and polarized gravitational waves [100][101][102][103][104].…”