Multiphonon excitations from dark matter scattering in crystals

Abstract

For direct detection of sub-MeV dark matter, a promising strategy is to search for individual phonon excitations in a crystal. We perform an analytic calculation of the rate for light dark matter (keV < m DM < MeV) to produce two acoustic phonons through scattering in cubic crystals such as GaAs, Ge, Si and diamond. The multiphonon rate is always smaller than the rate to produce a single optical phonon, whenever the latter is kinematically accessible. In Si and diamond there is a dark matter mass range for which multiphonon production can be the most promising process, depending on the experimental threshold.

Plasmon production from dark matter scattering

“…Note that for plasmon decays yielding ∼5 electrons on average, it is not necessary to assume zero background in the 1-or 2-electron bins, where there may in fact be large backgrounds in a realistic experimental analysis. The total plasmon rate is calculated assuming E R > 100 meV; for lower energies, the ion kinematics assumed here are no longer accurate and single-and multiphonon [17] production will start to dominate. The turnover in the sensitivity curves at around m χ ≈ 30 MeV is due to our choice of threshold E R .…”

“…As experiments lower their energy thresholds, collective many-body effects can become increasingly important and enhance the discovery potential beyond that of traditional searches for hard nuclear recoils. Examples can be found in numerous theoretical studies of direct detection of sub-GeV dark matter, including with semiconductors [2][3][4][5], superconductors [6][7][8], Dirac materials [9][10][11][12][13], phonon excitations in crystals [14][15][16][17], phonons in superfluid He [18][19][20], and others.…”

Describing the Migdal effect with a bremsstrahlung-like process and many-body effects

“…Owing to the continuous developments in detector technologies in recent years, the frontier of the dark matter direct detection has been pushed to the mass range below the GeV scale, where the traditional detection methods based on the nuclear scattering are expected to lose sensitivity. So more and more theorists and experimentalists have begun to shift to other alternative proposals based on new detection channels and materials, such as with semiconductors [1][2][3][4], Dirac materials [5][6][7], superconductors [8,9], superfluid helium [10][11][12], and via phonon excitations [13][14][15] and bremsstrahlung photons [16][17][18], as well as other proposals and analyses .…”

Effective Field Theory for Acoustic and Pseudo-Acoustic Phonons in Solids

“…One promising application of this is in the use of EFTs for describing the interactions of sub-GeV dark matter with a detector: when the de Broglie wavelength of the dark matter is large, an effective description of the coupling between dark matter and collective modes is necessary. For example, the relativistic approach could provide useful insights into cancellation mechanisms that have been observed in low-mass dark matter scattering rates in various detector materials [21,[31][32][33]. 3 Conventions: We work in natural units, = c = 1, and adopt a "mostly plus" metric, η µν = diag(−1, 1, 1, .…”