Infrared Freeze-In of Magnetic Dipole Dark Matter

TL;DR

This paper introduces a new infrared freeze-in mechanism for keV to GeV mass magnetic dipole dark matter, emphasizing the role of heavy charged states with masses comparable to dark matter, and explores its implications for detection.

Contribution

It presents a novel infrared freeze-in production scenario involving kinetically mixed $U(1)'$ charged states with masses near the dark matter mass, differing from previous ultraviolet-sensitive models.

Findings

Identifies parameter space consistent with cosmological constraints.

Proposes benchmark scenarios for direct detection experiments.

Highlights the importance of heavy charged states in dark matter production.

Abstract

We propose a novel mechanism for the cosmological production of keV - GeV mass dark matter that interacts with the Standard Model through a small effective magnetic dipole moment. Such an interaction can be radiatively generated if dark matter couples to heavier charged particles. Previous studies have focused on the case where these charged states are much heavier than the reheat temperature, such that freeze-in production of dark matter is sensitive to the ultraviolet details of reheating. Here, we instead consider the possibility that these heavy states have masses comparable to the dark matter mass and are charged under a new kinetically-mixed $U(1)'$. As a result, dark matter production is dominated by the infrared freeze-in of the heavy charged states that subsequently thermalize the rest of the dark sector to a temperature much below that of the visible bath. We delineate regions of parameter space consistent with cosmological and astrophysical constraints and identify benchmark scenarios that can guide the next generation of direct detection experiments searching for spin-dependent scattering of sub-GeV dark matter.