Abstract
We present a new class of direct detection signals; absorption of fermionic dark matter. We enumerate the operators through dimension six which lead to fermionic absorption, study their direct detection prospects, and summarize additional constraints on their suppression scale. Such dark matter is inherently unstable as there is no symmetry which prevents dark matter decays. Nevertheless, we show that fermionic dark matter absorption can be observed in direct detection and neutrino experiments while ensuring consistency with the observed dark matter abundance and required lifetime. For dark matter masses well below the GeV scale, dedicated searches for these signals at current and future experiments can probe orders of magnitude of unexplored parameter space.
Highlights
The search for dark matter (DM) is rapidly expanding both theoretically and experimentally
To discover these lighter DM candidates, the direct detection program is moving toward detecting smaller energy deposits with novel scattering targets and lowerthreshold detectors [14,15,16,17,18,19,20,21,22,23]
Candidates with studies of fermionic absorption signals limited to induced proton-to-neutron conversion in superKamiokande [33] and sterile neutrino DM [34,35,36,37,38,39,40,41]
Summary
We present a new class of direct detection signals; absorption of fermionic dark matter. We enumerate the operators through dimension six which lead to fermionic absorption, study their direct detection prospects, and summarize additional constraints on their suppression scale. Such dark matter is inherently unstable as there is no symmetry which prevents dark matter decays. Consider first dimension-6 operators of the form, 1⁄2χΓiν1⁄2ψ Γjψ, where ψ ⊃ fn; p; e; νg and Γi 1⁄4 f1; γ5; γμ; γμγ; σμνg denotes the different possible Lorentz structures of the bilinear These “neutral current” operators generate the first class of new signals we consider; ðχ−Þ þ T → ð−νÞ þ T, where T is a target nucleus or electron which absorbs a fraction of the DM mass energy. We will focus on nuclear absorption, where the rates may be coherently enhanced, and postpone the study of electron absorption [44]
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