Imprint of ultralight vector fields on gravitational wave propagation

Abstract

We study the effects of ultralight vector field (ULVF) dark matter on gravitational wave propagation. We find that the coherent oscillations of the vector field induce an anisotropic suppression of the gravitational wave amplitude as compared to the standard cosmology prediction. The effect is enhanced for smaller vector field masses and peaks for modes aroundThe suppression is negligible for astrophysically generated gravitational waves but could be sizable for primordial gravity waves. We discuss the possibility of detecting such an effect on the tensor power spectrum with future cosmic microwave background B-mode polarization detectors. We find that for the sensitivity of the upcoming LiteBIRD mission, the correction to the tensor power spectrum at decoupling time could be distinguishable from that of ΛCDM for ULVF masses m ≲ 10 −26 eV and sufficiently large abundances.

Vector dark radiation and gravitational-wave polarization

“…2 shows a particular example of this multipole decomposition for the different Stokes parameters evaluated today. We see the suppression of power in the monopole I 0 at large scales with respect to ΛCDM similarly to that found for vector dark matter [12] and the generation of a quadrupole and hexadecapole contributions which are absent in ΛCDM, whereas higher multipoles are negligible. On the other hand, we also see a large degree of polarization with a monopole distribution and also nonnegligible polarization with a quadrupolar and hexadecapolar distribution patterns.…”

Vector dark radiation and gravitational-wave polarization

“…Even though at the background level the vector field configurations we will consider behave as isotropic perfect fluids, the presence of the background vector fields induces non-vanishing anisotropic stresses in the perturbed energy-momentum tensor. As shown in [12], such anisotropic stresses modify the propagation equation of gravitational waves. Notice that this type of effect is not generated by cosmological scalar fields.…”

“…Thus, apart from the suppression of the matter power spectrum on small scales which is typical of any fuzzy dark matter model, the presence of the background vector field induces a mixing between scalar, vector and tensor modes which allows the generation of gravitational waves (GWs) from the usual density perturbations [11]. In addition, the propagation of tensor modes is also modified with respect to standard General Relativity inducing an anisotropic suppression of the tensor power spectrum on large scales [12].…”

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].…”