Ultraviolet freezein and nonstandard cosmologies
Abstract
A notable feature of UV freezein 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 nonstandard 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 spin2 portal (as might arise in bimetric gravity models). We comment on the transition from kination domination to radiation domination as a motivated example of nonstandard cosmologies.
 Publication:

Journal of Cosmology and Astroparticle Physics
 Pub Date:
 November 2019
 DOI:
 10.1088/14757516/2019/11/026
 arXiv:
 arXiv:1909.07992
 Bibcode:
 2019JCAP...11..026B
 Keywords:

 High Energy Physics  Phenomenology;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 22 pages, 5 figures