Abstract
The cosmological abundance of dark matter can be significantly influenced by the temperature dependence of particle masses and vacuum expectation values. We illustrate this point in three simple freeze-in models. The first one, which we call kinematically induced freeze-in, is based on the observation that the effective mass of a scalar temporarily becomes very small as the scalar potential undergoes a second order phase transition. This opens dark matter production channels that are otherwise forbidden. The second model we consider, dubbed vev-induced freeze-in, is a fermionic Higgs portal scenario. Its scalar sector is augmented compared to the Standard Model by an additional scalar singlet, S, which couples to dark matter and temporarily acquires a vacuum expectation value (a two-step phase transition or “vev flip-flop”). While 〈S〉 ≠ 0, the modified coupling structure in the scalar sector implies that dark matter production is significantly enhanced compared to the 〈S〉 = 0 phases realised at very early times and again today. The third model, which we call mixing-induced freeze-in, is similar in spirit, but here it is the mixing of dark sector fermions, induced by non-zero 〈S〉, that temporarily boosts the dark matter production rate. For all three scenarios, we carefully dissect the evolution of the dark sector in the early Universe. We compute the DM relic abundance as a function of the model parameters, emphasising the importance of thermal corrections and the proper treatment of phase transitions in the calculation.
Highlights
In kinetic and chemical equilibrium, until eventually Hubble expansion dilutes the DM density to the extent that DM annihilation into SM particles ceases
Its scalar sector is augmented compared to the Standard Model by an additional scalar singlet, S, which couples to dark matter and temporarily acquires a vacuum expectation value
While S = 0, the modified coupling structure in the scalar sector implies that dark matter production is significantly enhanced compared to the S = 0 phases realised at very early times and again today
Summary
In thermal quantum field theory, particle masses can receive temperature-dependent corrections from self-energy diagrams and become functions of T themselves. The SM Higgs mass is mh(T = 0) = 125 GeV today, but was much larger in the very early Universe and close to zero around the time of the electroweak cross-over at TEW 165 GeV. We discuss a scenario where the kinematics of the DM freeze-in rate are controlled by the mass of a new real scalar S
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have