If a GUT-scale phase transition occured after inflation, large domains in different vacuum states could be produced via the Kibble mechanism. The resulting network of scaling seeds supports horizon-scale density perturbations at all time (as shown in the below cartoon), stirring the baryon-photon plasma, which then generates CMB spectral distortions as the perturbations diffusively damp. Mustafa Amin and I computed the CMB spectral distortion signature of such a transition, produced by the scalar density perturbations produced by scaling seeds. The growth of scaling-seed density fluctuations is shown in the above figure, along with their damping (shaded in red) during the diffusion-damping era. The upshot of our investigation is that a scaling seed transition consistent with Planck constraints could be subsequently detected by a CMB spectral distortion mission like PIXIE.
In collaboration with Mustafa Amin.