Dilution of dark matter relic density in singlet extension models

TL;DR

This paper investigates how strong electroweak phase transitions in singlet extension models can dilute dark matter relic density, finding that dilution is limited but can impact certain parameter spaces.

Contribution

It provides a comparative analysis of dilution effects in xSM, 2HDM+S, and NMSSM models, highlighting the conditions under which dilution is significant.

Findings

Dilution of dark matter density can reach up to one-third.

In xSM and NMSSM, dilution is negligible due to phase transition timing.

In 2HDM+S, dilution can help recover viable dark matter parameter space.

Abstract

We study the dilution of dark matter (DM) relic density caused by the electroweak first-order phase transition (FOPT) in the singlet extension models, including the singlet extension of the standard model (xSM), of the two-Higgs-doublet model (2HDM+S) and the next-to-minimal supersymmetric standard model (NMSSM). We find that in these models the entropy released by the strong electroweak FOPT can dilute the DM density to 1/3 at most. Nevertheless, in the xSM and NMSSM where the singlet field configure is relevant to the phase transition temperature, the strong FOPT always happens before the DM freeze-out, making the dilution effect negligible for the current DM density. On the other hand, in the 2HDM+S where the DM freeze-out temperature is independent of FOPT, the dilution may salvage some parameter space excluded by excessive DM relic density or by DM direct detections.