Particle Dark Matter Density and Entropy Production in the Early Universe

Arnab Chaudhuri,Maxim Yu Khlopov,Shiladitya Porey

doi:10.3390/sym14020271

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.

Highlights

The early universe is associated with the high temperature and density of particles
As shown in this paper, the preexisting baryon asymmetry, and the frozen out Dark Matter (DM) density of the universe can be diluted significantly due to electroweak phase transition. Such dilution can take place for DM particles with the mass m 5 TeV, particles interacting with plasma with cross-section σ ≤ (Tc MPl)−1 and primordial black holes (PBH) with mass
(5.6 × 1028 gram or 3 × 10−5 M for Standard Model (SM) and 3 × 1028 gram or 1.5 × 10−5 M for 2HDM (Tc = 245 GeV)). These types of DM are frozen out, decoupled, frozen in, or formed before electroweak phase transition (EWPT). Their dilution is achieved with the influx of entropy into the primordial plasma, which was in the state of thermal equilibrium before the onset of EWPT

Summary

Introduction

The early universe is associated with the high temperature and density of particles. In accordance with the Big Bang theory, the temperature during the very early stages of expansion ranged from few eV to Planck scale ∼ MPl ∼ 1019 GeV (more precisely to reheating temperature in inflationary models). The number density of the frozen out species are conserved in the early universe but there can be some periods when their dilution is possible due to the influx of entropy into the plasma.

Results

Conclusion