# Forbidden frozen-in dark matter

## TL;DR

This paper explores a novel dark matter production mechanism via freeze-in, emphasizing the role of large thermal corrections to mediator masses at high temperatures, which can dominate dark matter generation.

## Contribution

It introduces the significance of thermally corrected mediator decays in dark matter production, expanding the standard freeze-in paradigm with new parameter space considerations.

## Key findings

- Thermal corrections can enable forbidden mediator decays to dominate dark matter production.
- The model identifies parameter ranges consistent with observed dark matter abundance.
- Constraints from collider, cosmological, and astrophysical data are applied to the new mechanism.

## Abstract

We examine and point out the importance of a regime of dark matter production through the freeze-in mechanism that results from a large thermal correction to a decaying mediator particle mass from hot plasma in the early Universe. We show that mediator decays to dark matter that are kinematically forbidden at the usually considered ranges of low temperatures can be generically present at higher temperatures and actually dominate the overall dark matter production, thus leading to very distinct solutions from the standard case. We illustrate these features by considering a dark Higgs portal model where dark matter is produced via decays of a scalar field with a large thermal mass. We identify the resulting ranges of parameters that are consistent with the correct dark matter relic abundance and further apply current and expected future collider, cosmological, and astrophysical limits.