Ultraviolet freeze-in and non-standard cosmologies

Abstract

A notable feature of UV freeze-in is that the relic density is strongly dependent on the highest temperatures of the thermal bath, and a common assumption is that the relevant "highest temperature" should be the reheating temperature after inflation T RH . However, the temperature of the thermal bath can be significantly higher in certain scenarios, reaching a value denoted T max , a fact which is only apparent away from the instantaneous decay approximation. Interestingly, it has been shown that if the operators are of sufficiently high mass dimension then the dark matter abundance can be enhanced by a "boost factor" depending on (T max /T RH ) relative to naive estimates assuming instantaneous reheating. We highlight here that in non-standard cosmological histories the critical mass dimension of the operator above at which the instantaneous decay approximation breaks down, and the exponent of the boost factor, depend on the equation of state ω prior to reheating. We highlight four examples in which the dark matter abundance receives a significant enhancement in the context of gravitino dark matter, the moduli portal, the Higgs portal, and the spin-2 portal (as might arise in bimetric gravity models). We comment on the transition from kination domination to radiation domination as a motivated example of non-standard cosmologies. arXiv:1909.07992v1 [hep-ph]

Kaluza-Klein FIMP dark matter in warped extra-dimensions

“…In particular, it has been observed that if the DM is produced during the transition from matter to radiation domination via an interaction rate that scales like γ(T ) ∝ T n , for n > 12 the DM abundance is enhanced by a boost factor proportional to (T max /T rh ) n−12 [66], whereas for n ≤ 12 the difference between the standard UV freeze-in calculation differ only by an O(1) factor from calculations taking into account non-instantaneous reheating. More recently, it has been highlighted that the critical mass dimension of the operator at which the instantaneous decay approximation breaks down depend on the equation of state ω, or equivalently, to the shape of the inflationary potential at the reheating epoch [67][68][69]. Therefore, the exponent of the boost factor becomes (T max /T rh ) n−nc with n c ≡ 6 + 2 3−ω 1+ω , showing a strong dependence on the equation of state [67].…”

“…More recently, it has been highlighted that the critical mass dimension of the operator at which the instantaneous decay approximation breaks down depend on the equation of state ω, or equivalently, to the shape of the inflationary potential at the reheating epoch [67][68][69]. Therefore, the exponent of the boost factor becomes (T max /T rh ) n−nc with n c ≡ 6 + 2 3−ω 1+ω , showing a strong dependence on the equation of state [67]. Subsequent papers have explored the impact of this boost factor in specific models [4,[70][71][72][73][74][75][76][77][78][79][80].…”

FIMP Dark Matter in Clockwork/Linear Dilaton extra-dimensions

“…In a more realistic picture, in which the instantaneous decay approximation is not used for reheating, the SM bath temperature may initially display a temperature much higher than T rh at onset of the radiation domination [67]. UV freeze-in is highly sensitive to the dynamics of the thermal bath during the intermediate period between inflation and radiation domination [68,69] and, therefore, it is natural to be analyzed within a specific heating setup (for related studies, see e.g. refs.…”

Neutron decay to a non-Abelian dark sector

“…Thereby, in this paper, we explore another avenue. We assume dark sector particles start with zero abundance in the early universe and they get produced through the freezein mechanism [66][67][68][69][70][71][72]. Consequently, in our setup, we need the maximum temperature T max to be smaller than m Φ i so that they are not produced in the early universe.…”