Dark matter pair absorption

TL;DR

This paper analyzes how atomic transitions can detect light dark matter through pair absorption, offering new constraints on bosonic dark matter and the cosmic neutrino background, especially for low-mass particles.

Contribution

It introduces the concept of pair absorption in atomic transitions as a novel method to constrain light dark matter and neutrino overdensities, expanding detection possibilities beyond scattering.

Findings

Pair absorption can constrain bosonic dark matter with μeV to eV masses.

Spin-flip transitions set strong limits on neutrino overdensity for low masses.

Pair absorption is insensitive to light fermionic dark matter due to low density.

Abstract

We present a comprehensive analysis of the sensitivity of atomic transitions to light dark matter pair absorption. Unlike scattering, where only a fraction of the dark matter energy is deposited, pair absorption processes absorb the full mass, and are therefore capable of constraining far lighter dark matter. Spin-flip and fine structure transitions are able to constrain electroweak scale axial-vector couplings for bosonic dark matter with $\mu\mathrm{eV}$ to eV masses, whilst principal quantum number transitions are able to set similar constraints on bosonic dark matter with scalar couplings. Unfortunately, pair absorption is largely insensitive to light fermionic DM due its necessarily tiny density at low masses. We also demonstrate the sensitivity of pair absorption to the cosmic neutrino background, and find that spin-flip transitions can set constraints on the overdensity parameter of $\eta_\nu \lesssim 10^9$ for neutrino masses $m_\nu \lesssim 1\,\mathrm{meV}$, around a hundred times stronger than existing constraints.