Probing early-universe phase transitions with CMB spectral distortions

Amplitude of a density perturbation produced by scaling seeds, beginning with super-horizon evolution, on through horizon entry and diffusion damping. Amplitude is plotted as a function of conformal time (in units of the inverse mode number), that is, as a function of the inverse fraction of the horizon subtended by a mode comoving wavelength as a function of time.

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.

Results published in arXiv: 1405.1039 (Phys. Rev. D 90, 083529).

In collaboration with Mustafa Amin.

Spectral distorter extraordinaire Mustafa Amin