The impact of a strongly first-order phase transition on the abundance
  of thermal relics
  We study the impact of a strongly first-order electro-weak phase transition
on the thermal relic abundance of particle species that could constitute the
dark matter and that decoupled before the phase transition occurred. We define
a dilution factor induced by generic first-order phase transitions, and we
explore the parameter space of the minimal supersymmetric extension to the
Standard Model to determine which phase transition temperatures and dilution
factors are relevant for the lightest neutralino as a dark matter candidate. We
then focus on a specific toy-model setup that could give rise to a strongly
first-order electro-weak phase transition, and proceed to a detailed
calculation of dilution factors and transition temperatures, comparing our
findings to actual neutralino dark matter models. Typical models that would
produce an excessive thermal relic density and that can be salvaged postulating
a strongly first-order electro-weak phase transition include massive
(multi-TeV) wino or higgsino-like neutralinos, as well as bino-like neutralinos
in a wider mass range, with masses as low as 400 GeV. If LHC data indicate an
inferred thermal neutralino relic abundance larger than the cold dark matter
density, the mismatch could thus potentially be explained by electro-weak scale
physics that will also be thoroughly explored with collider experiments in the
near future.
