Earth as a transducer for axion dark-matter detection
Ariel Arza, Michael A. Fedderke, Peter W. Graham, Derek F. Jackson Kimball, Saarik Kalia
Abstract
We demonstrate that ultralight axion dark matter with a coupling to photons induces an oscillating global terrestrial magnetic-field signal in the presence of the background geomagnetic field of the Earth. This signal is similar in structure to that of dark-photon dark matter that was recently pointed out and searched for in [Fedderke et al. Phys. Rev. D 104, 075023 (2021)] and [Fedderke et al. Phys. Rev. D 104, 095032 (2021)]. It has a global vectorial pattern fixed by the Earth's geomagnetic field, is temporally coherent on long timescales, and has a frequency set by the axion mass ${m}_{a}$. In this work, we both compute the detailed signal pattern and undertake a search for this signal in magnetometer network data maintained by the SuperMAG Collaboration. Our analysis identifies no strong evidence for an axion dark-matter signal in the axion mass range $2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}18}\text{ }\text{ }\mathrm{eV}\ensuremath{\lesssim}{m}_{a}\ensuremath{\lesssim}7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}17}\text{ }\text{ }\mathrm{eV}$. Assuming the axion is all of the dark matter, we place constraints on the axion-photon coupling ${g}_{a\ensuremath{\gamma}}$ in the same mass range; at their strongest, for masses $3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}17}\text{ }\text{ }\mathrm{eV}\ensuremath{\lesssim}{m}_{a}\ensuremath{\lesssim}4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}17}\text{ }\text{ }\mathrm{eV}$, these constraints are comparable to those obtained by the CAST helioscope.