Abstract
We point out that a nonrelativistic approximately 2 GeV dark matter (DM) which interacts with visible matter through higher-dimensional Rayleigh operators could explain the excess of ``electron recoil'' events recently observed by the XENON1T Collaboration. A DM scattering event results in a few keV photon that on average carries most of the deposited energy, while the nuclear recoil energy is only a subleading correction. Since the XENON1T detector does not discriminate between electrons and photons, such events would be interpreted as excess of the keV electrons. Indirect constraints from dark matter annihilation are avoided for light mediators of $\mathcal{O}(10\text{ }\text{ }\mathrm{MeV})$ that have sizable couplings to neutrinos. One-loop induced spin-independent scattering in dark matter may soon lead to a confirmation signal or already excludes regions of viable parameter space for the Rayleigh DM model, depending on what the exact values of the unknown nonperturbative nuclear matrix elements are.
Highlights
The XENON1T Collaboration recently announced the results of a search for dark matter (DM) using electronic recoils after 0.65 ton-yr of exposure [1]
The intriguing electron recoil excess events in XENON1T can be due to nonrelativistic DM scattering off nuclei, if the scattering is induced by Rayleigh operators, since the XENON1T detector does not discriminate between electrons and photons
We have showed that viable parameter space exists for the case of MeV scale mediators
Summary
The XENON1T Collaboration recently announced the results of a search for dark matter (DM) using electronic recoils after 0.65 ton-yr of exposure [1]. A number of alternative explanations have been proposed: fast moving DM particles scattering on electrons [9,10], nonstandard neutrino interactions mediated by light new particles [11], hidden photon dark matter [12], etc. We propose a third possibility, that the anomalous events are due to electromagnetic interactions of nonrelativistic DM with xenon nuclei. The observed excess events are unmistakably of the “electron recoil” type (energy deposited in photons and/or electrons), which seems to rule out the possibility of elastic scatterings of nonrelativistic DM. The exception to this naive conclusion is DM that couples to the visible sector through the Rayleigh operator, φφFμνFμν. This gives important constraints on the model
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