Broadband phonon production from axion absorption

• Main Authors: Bloch, Itay M, Knapen, Simon, Madden, Amalia, Marocco, Giacomo
• Format: Journal Article
• Language: English
• Published: 15-11-2024
• Subjects: Physics - High Energy Physics - Phenomenology
• DOI: 10.48550/arxiv.2411.10542

We show that axion dark matter in the range meV $\lesssim m_a\lesssim$ 100
meV can incoherently excite phonons in crystal targets with unpolarised nuclear
spins. This can occur through its coupling to nuclear spins and/or through its
induced time-dependent electric dipole moment in nuclei. Due to the random
orientation of the nuclear spins, translation symmetry is broken in the phonon
effective theory, allowing axion absorption to create phonons with unrestricted
momentum. The absorption rate is therefore proportional to the phonon density
of states, which generically has support across a wide range of energies,
allowing for a broadband detection scheme. We calculate the absorption rate for
solid $\text{H}_2$, $\text{D}_2$, $\text{Al}_2\text{O}_3$, $\text{GaAs}$,
$\text{H}_2\text{O}$, $\text{D}_2\text{O}$, $\text{Be}$ and $\text{Li}_2
\text{O}$, and find that materials containing light, non-zero spin nuclei are
the most promising. The predicted rates for the QCD axion are of the order of a
few events / 10 kg-year exposure, setting an ambitious target for the required
exposure and background suppression.