Particle dark matter density and entropy production in the early universe

TL;DR

This paper investigates how entropy production during the electroweak phase transition in the early universe can dilute dark matter density, comparing the standard model and two-Higgs doublet model scenarios.

Contribution

It introduces a comparative analysis of entropy production effects in the SM and 2HDM during EWPT and their impact on dark matter density dilution.

Findings

Entropy production during EWPT can significantly dilute dark matter density.

First-order EWPT in 2HDM leads to more entropy release than second-order in SM.

Dilution effects are relevant for various dark matter candidates including primordial black holes.

Abstract

Dark Matter (DM) density is reduced if entropy production takes place after DM particles abundance is frozen out in the early universe. We study a possibility of such reduction due to entropy production in the electroweak phase transition (EWPT). We compare scenarios of entropy production in the standard model (SM) and its simplest extension, the two-Higgs doublet model (2HDM). Assuming the EWPT is of second order in the SM scenario and the first order in the 2HDM, we calculate the entropy release in these scenarios and the corresponding dilution of preexisting DM density in the early universe. We find the effect of dilution in EWPT significant for confrontation with observations of any form of possible DM (including primordial black holes (PBHs)), which is frozen out, decoupled, frozen in, or formed before EWPT.