2025/11/21(Fri)
10:00 -11:30
Online Seminar
視訊演講 Video Seminar [ Meeting Link / ID: / Password: ]
Title
Ultra-relativistic freeze-out: a bridge from WIMPs to FIMPs
Speaker
Dr. Stephen Henrich (University of Minnesota Twin Cities)Abstract
We re-examine the case for dark matter (DM) produced by ultra-relativistic freeze-out (UFO). UFO is the mechanism by which Standard Model (SM) neutrinos decouple from the radiation bath in the early universe at a temperature $T_{d} \approx 1$ MeV. This corresponds to chemical freeze-out without Boltzmann suppression. While UFO has historically been rejected as a viable mechanism for DM production due to its association with hot DM and the accompanying incompatibility with $\Lambda$CDM, we show that when the approximation of instantaneous reheating after inflation is lifted, UFO can produce cold DM and account for the entire observed relic density in large regions of parameter space. We delineate the conditions on the thermally averaged cross section required for a given particle physics process to be compatible with UFO, and we demonstrate that UFO is a robust intermediate regime between the standard WIMP and FIMP scenarios. This mechanism does not require fine tuning. In particular, we find that UFO during reheating can produce the correct relic density ($\Omega_{\chi}h^2 = 0.12$) for DM masses spanning about 13 orders of magnitude, reheating temperatures spanning 17 orders of magnitude, and beyond the Standard Model (BSM) effective interaction scales spanning 11 orders of magnitude.
Language
演講語言 (Language): in English
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