Ultralight Millicharged Dark Matter via Misalignment

TL;DR

This paper introduces a new model for ultralight millicharged dark matter produced via the misalignment mechanism, compatible with cosmological observations and testable by upcoming experiments.

Contribution

It proposes a concrete non-thermal production model for millicharged dark matter using a spontaneously broken symmetry, expanding the viable parameter space.

Findings

The model is consistent with observed dark matter abundance.

New parameter space accessible to future experiments.

Phenomenology compatible with existing experimental constraints.

Abstract

We explore the cosmology and phenomenology of millicharged and millicharge-like dark matter with masses from 1 eV to 10 keV and charges of $10^{-18}$ to $10^{-14}$. Dark matter in this mass range cannot be thermally produced, but can arise from non-thermal mechanisms. We propose a concrete model employing a spontaneously broken approximate global symmetry, in which millicharged dark matter is produced via the misalignment mechanism. We show that this production mechanism is cosmologically consistent and compatible with the observed dark matter abundance. This model can be implemented using either fundamental scalars or hidden-sector quarks, and coupled either to the Standard Model photon or to a hidden photon. We then consider the phenomenology of light millicharged dark matter, regardless of its cosmological origin, and determine the parameter space consistent with existing experiments and observations. A significant part of the new parameter space we consider may be accessible in the near future through direct deflection experiments, measurements of the cosmic microwave background blackbody spectrum, and future constraints on plasma instabilities due to dark matter self-interaction.