Bridging the gap: spectral distortions meet gravitational waves

In this paper we provide a new method to constrain the energy density of gravitational waves at high redshifts using measurements of the µ-type spectral distortion of the CMB. We show that the µ-distortion is sensitive to gravitational waves with frequencies \(10^{-16} \lesssim f \lesssim 10^{-8}\) Hz, which is inaccessible to other probes. In particular, this range of frequencies bridges the gap between cosmological large-scale and astrophysical small-scale probes. We use this method to place new constraints on the energy density of gravitational waves at high redshifts.

Arxiv preprint

Published version

Upper limits on the energy density of gravitational waves from measurements of µ-distortions for various experimental configurations