Probing early-universe phase transitions with CMB spectral distortions

Understand

Global, symmetry-breaking phase transitions in the early universe can generate scaling seed networks which lead to metric perturbations.

• The acoustic waves in the photon-baryon plasma sourced by these metric perturbations, when Silk damped, generate spectral distortions of the cosmic microwave background (CMB).
• In this work, the chemical potential distortion ($\mu$) due to scaling seed networks is computed and the accompanying Compton $y$-type distortion is estimated.
• The specific model of choice is the $O(N)$ nonlinear $\sigma$-model for $N\gg 1$, but the results remain the same order of magnitude for other scaling seeds.