A Time-Varying Fine Structure Constant from Naturally Ultralight Dark Matter

TL;DR

This paper proposes models where an ultralight scalar dark matter field causes the fine structure constant to oscillate over time, with potential observability in current experiments.

Contribution

It introduces a novel mechanism linking ultralight scalar dark matter to time-varying fundamental constants, protected by a discrete symmetry.

Findings

Oscillations in the fine structure constant are large enough for detection.

The scalar field's mass is stabilized against radiative corrections.

Dark matter abundance is explained via the misalignment mechanism.

Abstract

We present a class of models in which the coupling of the photon to an ultralight scalar field that has a time-dependent vacuum expectation value causes the fine structure constant to oscillate in time. The scalar field is assumed to constitute all or part of the observed dark matter. Its mass is protected against radiative corrections by a discrete $\mathbb{Z}_N$ exchange symmetry that relates the Standard Model to several copies to itself. The abundance of dark matter is set by the misalignment mechanism. We show that the oscillations in the fine structure constant are large enough to be observed in current and near-future experiments.