Shaping Dark Photon Spectral Distortions

TL;DR

This paper uses COBE-FIRAS data to set new limits on dark photon interactions with photons, improving previous bounds by accounting for redshift evolution and spectral shape of distortions, aiding future CMB searches.

Contribution

It introduces a detailed redshift-dependent analysis of CMB spectral distortions caused by photon-dark photon oscillations, refining constraints over previous methods.

Findings

Established new bounds on dark photon masses from 10^{-10} to 10^{-4} eV.

Highlighted the importance of spectral shape analysis for future CMB missions.

Demonstrated the significance of redshift evolution in spectral distortion modeling.

Abstract

The cosmic microwave background (CMB) spectrum is an extraordinary tool for exploring physics beyond the Standard Model. The exquisite precision of the measurement makes it particularly sensitive to small effects caused by hidden sector interactions. In particular, CMB spectral distortions can unveil the existence of dark photons which are kinetically coupled to the standard photon. In this work, we use the COBE-FIRAS dataset to derive accurate and robust limits on photon-to-dark-photon oscillations for a large range of dark photon masses, from $10^{-10}$ to $10^{-4}$ eV. We consider in detail the redshift dependence of the bounds, computing CMB distortions due to photon injection/removal using a Green's function method. Our treatment improves on previous results, which had set limits studying energy injection/removal into baryons rather than photon injection/removal, or ignored the redshift evolution of distortions. The difference between our treatment and previous ones is particularly noticeable in the predicted spectral shape of the distortions, a smoking gun signature for photon-to-dark-photon oscillations. The characterization of the spectral shape is crucial for future CMB missions, which could improve the present sensitivity by orders of magnitude, exploring regions of the dark photon parameter space that are otherwise difficult to access.