Abstract
We study the stochastic background of gravitational waves which accompany the sudden freeze-out of dark matter triggered by a cosmological first order phase transition that endows dark matter with mass. We consider models that produce the measured dark matter relic abundance via (1) bubble filtering, and (2) inflation and reheating, and show that gravitational waves from these mechanisms are detectable at future interferometers.
Highlights
We study the stochastic background of gravitational waves which accompany the sudden freeze-out of dark matter triggered by a cosmological first order phase transition that endows dark matter with mass
We consider a first order phase transition (FOPT) in the early universe, with vacuum bubbles nucleated at temperature T, which ends with the expanding bubbles populating the entire universe; until we discuss inflationary supercooling, we do not differentiate between the nucleation temperature Tn and the temperature T at which gravitational waves are produced
We focus on gravitational wave (GW) signals of sudden DM freeze-out caused by a FOPT during which DM mass is generated
Summary
During the FOPT and bubble expansion, massless (massive) DM particles are located outside (inside) the bubble, and momentum conservation must be satisfied at the bubble wall. An incident DM particle enters the bubble if it carries kinetic energy larger than its mass inside the bubble. If a thermal flux of χ is incident on the wall, the number density of DM particles that enter the bubble is [14]. In the non-relativistic limit, vw → 0, filtering strongly suppresses the DM number density inside the bubble as e−mχ/T. Mχ/(γwT ) → 0, the number density ∼ e−mχ/(2γwT ), so there is very little filtering and niχn approaches the equilibrium number density outside the bubble, neχq|T =T = gDMT 3/π2. The DM relic abundances for three values of T and relativistic and non-relativistic wall velocities are shown in figure 1. That larger T requires larger mχ/T can be understood by combining eq (2.1) and (2.2): ΩDMh2 ∝ T (mχ/T ) e−mχ/T
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