Spectral signatures of axionlike dark matter

TL;DR

This paper derives the spectral line shapes for axionlike dark matter signals in haloscope experiments, including new results for gradient couplings and their directional and temporal modulations, aiding experimental detection.

Contribution

It extends previous models to include gradient couplings, revealing directional sensitivity and daily/annual modulations of the axion signal.

Findings

Derived spectral line shapes for axion-photon and axion-gluon couplings.

Identified directional dependence of the gradient coupling signal.

Discussed daily and annual modulation effects on the signal.

Abstract

We derive spectral line shapes of the expected signal for a haloscope experiment searching for axionlike dark matter. The knowledge of these line shapes is needed to optimize an experimental design and data analysis procedure. We extend the previously known results for the axion-photon and axion-gluon couplings to the case of gradient (axion-fermion) coupling. A unique feature of the gradient interaction is its dependence not only on magnitudes but also on directions of velocities of galactic halo particles, which leads to the directional sensitivity of the corresponding haloscope. We also discuss the daily and annual modulations of the gradient signal caused by the Earth's rotational and orbital motions. In the case of detection, these periodic modulations will be an important confirmation that the signal is sourced by axionlike particles in the halo of our Galaxy.