Freeze-in of WIMP dark matter

TL;DR

This paper introduces a new freeze-in mechanism for WIMP dark matter triggered by a first-order phase transition, which alters the DM density and mass, expanding the understanding of WIMP dark matter production.

Contribution

It proposes a novel freeze-in scenario driven by a first-order phase transition, demonstrating its viability with simplified and realistic models, and broadening the WIMP dark matter paradigm.

Findings

FOPT can dilute pre-existing DM density to zero.

WIMPs can be produced via freeze-in after FOPT despite not having feeble interactions.

The mechanism applies to models with delayed electroweak phase transition.

Abstract

The nature of dark matter (DM) remains one of the most important unanswered questions in particle physics. Here, we propose a novel scenario for DM in which weakly interacting massive particles (WIMPs) can freeze-in due to a first-order phase transition (FOPT) in the early Universe. The FOPT dilutes the pre-existing DM density to zero and leads to a sudden change in DM mass, preventing WIMPs from re-equilibrating due to their large mass-to-temperature ratio. Following the FOPT, WIMPs are produced via a freeze-in process, even though their interactions are NOT feeble. We demonstrate this concept using a simplified model and then apply it to a realistic model with a delayed electroweak phase transition. Our work presents a promising new direction for the freeze-in mechanism, and also extends the category of WIMP DM.