Next-to-Minimal Freeze-in Dark Matter

TL;DR

This paper explores extended models of freeze-in dark matter production, especially considering non-instantaneous reheating and higher SU(2) representations, revealing new experimental prospects.

Contribution

It introduces next-to-minimal extensions of minimal freeze-in dark matter, analyzing effects of non-instantaneous reheating and higher SU(2) representations.

Findings

Reheating dynamics significantly affect dark matter production.

Higher SU(2) representations can be probed in near-future experiments.

Non-instantaneous reheating scenarios expand viable dark matter models.

Abstract

If the dark matter mass exceeds the highest temperature of the thermal bath, then dark matter production is Boltzmann suppressed. This opens new possibilities for dark matter model building. In particular, WIMP models that are experimentally excluded can be revived in this setting; conversely, freeze-in models, which would typically be beyond experimental reach, are potentially discoverable in the Boltzmann suppressed regime. In a recent letter, we highlighted these aspects for the case of electroweak doublet fermion dark matter assuming instantaneous inflationary reheating. Due to its elegance and simplicity, we coin this {\em Minimal Freeze-in} (MFI) Dark Matter. Here we consider next-to-minimal extensions of MFI dark matter. We present the implications for non-instantaneous reheating, including scenarios beyond the standard picture in which the Universe is initially matter dominated prior to reheating. Furthermore, we explore model variations within the electroweak dark matter scenario. Specifically, we consider fermion dark matter in higher representations of SU(2)${}_L$, exploring the current limits and the near-future discovery potential.