Speaker
Description
Deviations of the CMB from a black body spectrum, so called spectral distortions, provide a powerful probe of the early universe. For example they can be sourced by gravitational waves (GWs) with frequencies too large to be probed by CMB polarization and too low for pulsar timing arrays. But what if your favorite source of GWs, e.g. a phase transition or cosmic defects, only sources the GWs as these modes enter the horizon? We show that in this case a much larger spectral distortion is caused through gravitationally induced acoustic waves in the baryon-photon fluid. We give an analytic estimate of this effect and compare to the numerical result of a toy model. Finally we show that spectral distortions can test and constraint a large class of purely gravitationally coupled sectors, complementing GW searches.
