CMB Spectral Distortions from an Axion-Dark Photon-Photon Interaction

TL;DR

This paper investigates how interactions between axions, dark photons, and photons can distort the cosmic microwave background spectrum, providing new constraints on these beyond Standard Model particles.

Contribution

It introduces and analyzes the effects of a mixed axion-photon-dark-photon interaction on the CMB spectrum, revealing stronger constraints than previous studies.

Findings

CMB spectral distortions can constrain axion-dark photon interactions.

The constraints are stronger than those on axion-photon couplings for many masses.

Unique distortion signatures help identify the presence of such interactions.

Abstract

The presence of a plethora of light spin 0 and spin 1 fields is motivated in a number of BSM scenarios, such as the axiverse. The study of the interactions of such light bosonic fields with the Standard Model has focused mostly on interactions involving only one such field, such as the axion ($\phi$) coupling to photons, $\phi F \tilde F$, or the kinetic mixing between photon and the dark photon, $ F F_D$. In this work, we continue the exploration of interactions involving two light BSM fields and the standard model, focusing on the mixed axion-photon-dark-photon interaction $\phi F \tilde F_D$. If either the axion or dark photon are dark matter, we show that this interaction leads to conversion of the CMB photons into a dark sector particle, leading to a distortion in the CMB spectrum. We present the details of these unique distortion signatures and the resulting constraints on the $\phi F \tilde F_D$ coupling. In particular, we find that for a wide range of masses, the constraints from these effect are stronger than on the more widely studied axion-photon coupling.