Particle dark matter density and entropy production in the early
  universe
  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.
