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We consider the direct detection of dark matter (DM) with polar materials, where single production of optical or acoustic phonons gives excellent reach to scattering of sub-MeV DM for both scalar and vector mediators. Using Density Functional Theory (DFT), we calculate the material-specific matrix elements, focusing on GaAs and sapphire, and show that DM scattering in an anisotropic crystal such as sapphire features a strong directional dependence. For example, for a DM candidate with mass 40 keV and relic abundance set by freeze-in, the daily modulation in the interaction rate can be established at 90% C.L. with a gram-year of exposure. Non-thermal dark photon DM in the meV - eV mass range can also be effectively absorbed in polar materials.
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We show that polar materials are excellent targets for direct detection of sub-GeV dark matter due to the presence of gapped optical phonons as well as acoustic phonons with high sound speed. We take the example of Gallium Arsenide (GaAs), which has the properties needed for experimental realization, and where many results can be estimated analytically. We find GaAs has excellent reach to dark photon absorption, can completely cover the freeze-in benchmark for scattering via an ultralight dark photon, and is competitive with other proposals to detect sub-MeV dark matter scattering off nuclei.
Superconducting detectors have been proposed as outstanding targets for the direct detection of light dark matter scattering at masses as low as a keV. We study the prospects for directional detection of dark matter in isotropic superconducting targets from the angular distribution of excitations produced in the material. We find that dark matter scattering produces initial excitations with an anisotropic distribution, and further show that this directional information can be preserved as the initial excitations relax. Our results demonstrate that directional detection is possible for a wide range of dark matter masses, and pave the way for light dark matter discovery with bulk superconducting targets.
Inelastic dark matter reconciles the DAMA anomaly with other null direct detection experiments and points to a non-minimal structure in the dark matter sector. In addition to the dominant inelastic interaction, dark matter scattering may have a subdominant elastic component. If these elastic interactions are suppressed at low momentum transfer, they will have similar nuclear recoil spectra to inelastic scattering events. While upcoming direct detection experiments will see strong signals from such models, they may not be able to unambiguously determine the presence of the subdominant elastic scattering from the recoil spectra alone. We show that directional detection experiments can separate elastic and inelastic scattering events and discover the underlying dynamics of dark matter models.
Directional detection of dark matter has sensitivity for both recoil energy and direction of nuclear recoil. It opens the way to measure local velocity distribution of dark matter. In this paper, we study possibility to discriminate isotropic distribution and anisotropic one suggested by a N-body simulation with directional detector. Numerical simulation is performed for two cases according to the detectors, one corresponds to angular histogram and the other is energy-angular distribution of the signals. We reveal that the anisotropy of velocity distribution can be discriminated at 90% C.L. with chi-squared test if O($10^4$) signals are obtained.
The direct detection of sub-GeV dark matter interacting with nucleons is hampered by to the low recoil energies induced by scatterings in the detectors. This experimental difficulty is avoided in the scenario of boosted dark matter where a component of dark matter particles is endowed with large kinetic energies. In this Letter, we point out that the current evaporation of primordial black holes with masses from $10^{14}$ to $10^{16}$ g is a source of boosted light dark matter with energies of tens to hundreds of MeV. Focusing on the XENON1T experiment, we show that these relativistic dark matter particles could give rise to a signal orders of magnitude larger than the present upper bounds. Therefore, we are able to significantly constrain the combined parameter space of primordial black holes and sub-GeV dark matter. In the presence of primordial black holes with a mass of $10^{15}~mathrm{g}$ and an abundance compatible with present bounds, the limits on DM-nucleon cross-section are improved by four orders of magnitude.
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