Freeze-in at Low Reheating and Direct Detection of Fermion Dark Matter

TL;DR

This paper explores a low-reheating-temperature freeze-in model of fermionic dark matter interacting via a pseudoscalar, analyzing production mechanisms, thermalization conditions, and prospects for direct detection experiments like LZ and DARWIN.

Contribution

It introduces a minimal fermionic dark matter model with a pseudoscalar mediator, detailing production, thermalization conditions, and experimental detection constraints.

Findings

Dark matter produced via pseudoscalar decay remains in thermal equilibrium under certain conditions.

Derived constraints from current and future direct detection experiments.

Identified parameter space compatible with low-reheating scenarios.

Abstract

We investigate a low-reheating-temperature freeze-in scenario within a minimal model of fermionic dark matter interacting through a pseudoscalar mediator. In this setup, dark matter is produced via the decay of the pseudoscalar, which remains in thermal equilibrium with the Standard Model bath. We derive the thermalization and non-thermalization conditions for the new fields and obtain the corresponding direct-detection constraints and projections on the model based on LZ and DARWIN experiments, respectively.