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 keV up to the detector resolution, accounting for the recoil events over ER = 2 − 3 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′ mediator and provide microscopic models realizing the required dark matter and electron couplings to Z′.
Highlights
Exothermic dark matter and electron recoilWe begin with the kinematics for exothermic dark matter in the case of downscattering off the electron
The one inferred from the elastic scattering between the non-relativistic dark matter in the standard halo model and the electron
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
Summary
We begin with the kinematics for exothermic dark matter in the case of downscattering off the electron. We calculate the event rate for the electron recoil in the Xenon atoms by including the phase-space enhancement and the atomic excitation factor
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