Cosmological and Astrophysical Constraints on Late First-Order Phase Transitions

TL;DR

This paper investigates how late-time first-order phase transitions in a dark sector generate curvature perturbations that affect cosmological observables, providing new constraints on such transitions using diverse astrophysical data.

Contribution

It derives universal features of curvature perturbations from late dark sector phase transitions and constrains their properties through multiple astrophysical observations.

Findings

Constraints on dark sector phase transition parameters from Planck data.

Limits from baryon acoustic oscillations and Lyman-alpha observations.

Implications for early reionization and ultra-faint dwarf galaxy formation.

Abstract

First-order cosmological phase transitions (PT) can take place in a dark sector at relatively late times between the big-bang nucleosynthesis and recombination epochs. Because bubble nucleation is stochastic, the PT completes at different times in different regions of the Universe. This fluctuation sources a curvature perturbation whose (dimensionless) power spectrum ${\cal P}_\zeta(k)$ features a universal infrared tail, independent of the microscopic details of the PT. Even in the absence of any non-gravitational interaction between the dark sector and the Standard Model, these additional curvature perturbations at small scales impact a variety of observables. We derive new constraints on dark sector phase transitions using {\it Planck}, baryon acoustic oscillation (BAO), Lyman-$\alpha$ observations, spectral distortion limits from FIRAS, constraints on early reionization, and the existence of ultra-faint dwarf galaxies.