Exothermic Dark Matter for XENON1T Excess

Abstract

Motivated by the recent excess in the electron recoil from XENON1T experiment, we consider the possibility of exothermic dark matter, which is composed of two states with mass splitting. The heavier state down-scatters off the electron into the lighter state, making an appropriate recoil energy required for the Xenon excess even for the standard Maxwellian velocity distribution of dark matter. Accordingly, we determine the mass difference between two component states of dark matter to the peak electron recoil energy at about $2.5\mathrm{keV}$ up to the detector resolution, accounting for the recoil events over $E_R=2-3\mathrm{keV}$, which are most significant. We include the effects of the phase-space enhancement and the atomic excitation factor to calculate the required scattering cross section for the Xenon excess. We discuss the implications of dark matter interactions in the effective theory for exothermic dark matter and a massive $Z^{\prime }$ mediator and provide microscopic models realizing the required dark matter and electron couplings to $Z^{\prime }$.

22 pages, 3 figures, v2: References added and typos corrected. Discussion on two-photon decay mode of dark matter added; v3: Dark matter decoupling clarified, discussion expanded on the recoil energy with electron velocity included, and figures added. Accepted to JHEP

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• Probing the relaxed relaxion and Higgs-portal with S1 & S2
• Self-interacting Inelastic Dark Matter in the light of XENON1T excess
• Implications of the XENON1T Excess on the Dark Matter Interpretation
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• Canonical seesaw implication for two-component dark matter
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• Xenon-1T excess as a possible signal of a sub-GeV hidden sector dark matter
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• Detection of Inelastic Dark Matter via Electron Recoils in SENSEI
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• Explorations of pseudo-Dirac dark matter having keV splittings and interacting via transition electric and magnetic dipole moments
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• Inelastic dark matter, small scale problems, and the XENON1T excess
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• Inelastic Dark Matter at the Fermilab Short Baseline Neutrino Program