DarkELF: A python package for dark matter scattering in dielectric targets

Abstract

We present a python package to calculate interaction rates of light dark matter in dielectric materials, including screening effects. The full response of the material is parametrized in the terms of the energy loss function (ELF) of material, which DarkELF converts into differential scattering rates for both direct dark matter electron scattering and through the Migdal effect. In addition, DarkELF can calculate the rate to produce phonons from sub-MeV dark matter scattering via the dark photon mediator, as well as the absorption rate for dark matter comprised of dark photons. The package includes precomputed ELFs for Al, Al2O3, GaAs, GaN, Ge, Si, SiO2, and ZnS, and allows the user to easily add their own ELF extractions for arbitrary materials.

DM-electron scattering in materials: sum rules and heterostructures

“…Especially at high DM masses, our toy model calculation will not be realistic. For m χ MeV, the characteristic momentum scale is m χ v 0 770 eV = 2π 1.6 nm , which is close enough to atomic lattice scales that the dielectric function will have non-negligible momentum dependence [25,35]. However, for m χ MeV, our calculations illustrate the kind of behaviour expected.…”

“…At frequencies ∼ 10−100 meV, polar materials can support optical phonon excitations, which can have dω ω Im(− −1 L ) up to ∼ 0.3 over the relevant frequency range [34] (at small k). Approximate energy-loss-function-based calculations of the DM scattering rate in such materials [35], as well as density functional theory calculations [16,36], indicate that they are promising candidates for DM detection [16,[36][37][38]. The SiO 2 curves in Figure 2 illustrate that, at DM masses in the ∼ 0.1 − 1 MeV range, the scattering rate into optical phonons can be within an order of magnitude of the sum rule bound.…”

“…These illustrate that the scattering rates are significantly below the theoretical optimum, especially for DM masses MeV or MeV. The solid SiO2 curve corresponds to an updated [39] density functional theory projection from [16] for phonons in quartz, and the dashed curve to an energy loss function calculation from [35], illustrating that scattering into optical phonons can approach the sum rule limit more closely at suitable DM masses. dynamics are effectively electrostatic.…”

“…The SiO 2 curves in Figure 2 illustrate that, at DM masses in the ∼ 0.1 − 1 MeV range, the scattering rate into optical phonons can be within an order of magnitude of the sum rule bound. 6 Other materials proposed for DM scattering experiments, such as aluminium or semiconductors, have response functions with most of their support at energies 10 eV [24,25,35], for low k. This means that their scattering rates are some way from the theoretical optimum, at all DM masses. For DM masses 20 MeV, the response function is concentrated at overly high frequencies, while for higher DM masses, the associated momentum transfers are 10 keV, which is large enough that Im −1 L (ω, k) is significantly reduced.…”

The Phonon Background from Gamma Rays in Sub-GeV Dark Matter Detectors

“…3, we extract the signal for the scalar mediators directly from Fig. 5 of [46], and use the DarkELF package [79] to calculate DM interacting with an ultralight (or massless) dark photon mediator. DarkELF utilizes the energy-loss-function Im −1 (ω) [81,82], a quantity that has both been measured and calculated from first principles.…”