Dark matter phonon coupling

Abstract

Generically, the effective coupling between the dark matter and an atom scales with the number of constituents in the atom, resulting in the effective coupling being proportional to the mass of the atom. In this limit, when the momentum transfer is also small, we show that the leading term in the scattering of a particle off the optical phonons of an array of atoms, whether in a crystal or in a molecule, vanishes. Next-generation dark matter direct detection experiments with sub-electron-volt energy thresholds will operate in a regime where this effect is important, and the suppression can be up to order 106 over naive expectations. For dark matter that couples differently to protons and neu..