Projected Sensitivity of DMRadio-m${}^3$: A Search for the QCD Axion Below $1\hat{I}¼$eV

Abstract

The QCD axion is one of the most compelling candidates to explain the dark matter abundance of the universe. With its extremely small mass ($\ll 1\mathrm{eV}/c^2$), axion dark matter interacts as a classical field rather than a particle. Its coupling to photons leads to a modification of Maxwell's equations that can be measured with extremely sensitive readout circuits. DMRadio-m${}^3$ is a next-generation search for axion dark matter below $1\hat{I}¼$eV using a $>4$ T static magnetic field, a coaxial inductive pickup, a tunable LC resonator, and a DC-SQUID readout. It is designed to search for QCD axion dark matter over the range $20\mathrm{neV}\lesssim m_a{c}^2\lesssim 800\mathrm{neV}$ ($5\mathrm{MHz}<\hat{I}½<200\mathrm{MHz}$). The primary science goal aims to achieve DFSZ sensitivity above $m_a{c}^2\approx 120$ neV (30 MHz), with a secondary science goal of probing KSVZ axions down to $m_a{c}^2\approx 40\mathrm{neV}$ (10 MHz).

8 pages, 4 figures. Updated to fix small errors and correct acknowledgements. Updated title and notational clarifications