Relic cosmological vector fields and inflationary gravitational waves

Abstract

We show that relic vector fields can significantly impact a spectrum of primordial gravitational waves in the post-inflationary era. We consider a triplet of U(1) fields in a homogeneous, isotropic configuration. The interaction between the gravitational waves and the vector fields, from the end of reheating to the present day, yields novel spectral features. The amplitude, tilt, shape, and net chirality of the gravitational wave spectrum are shown to depend on the abundance of the electric-and magnetic-like vector fields. Our results show that even a modest abundance can have strong implications for efforts to detect the imprint of gravitational waves on the cosmic microwave background polarization. We find that a vector field comprising less than 2% of the energy density during the radiation dominated era can have a greater than order unity effect on the predicted inflationary gravitational wave spectrum.

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].…”