Interpretation of XENON1T excess with MeV boosted dark matter * *The work of T. Li was supported by the National Natural Science Foundation of China (11975129, 12035008) and "the Fundamental Research Funds for the Central Universities", Nankai University (63196013). L.-B. Jia acknowledges support from the Longshan academic talent research supporting program of SWUST (18LZX415)

Abstract

The XENON1T excess of keV electron recoil events may be induced by the scattering of electrons and long-lived particles with an MeV mass and high speed. We consider a tangible model composed of two scalar MeV dark matter (DM) particles, and , to interpret the XENON1T keV excess via boosted . A small mass splitting is introduced, and the boosted can be produced using the dark annihilation process of via a resonant scalar ϕ. electron scattering is intermediated by a vector boson X. Although the constraints from Big Bang nucleosynthesis, cosmic microwave background (CMB), and low-energy experiments set the mediated electron scattering cross section to be , the MeV scale DM with a resonance enhanced dark annihilation today can still provide sufficient boosted and induce the XENON1T keV excess. The relic density of is significantly reduced by the s-wave process , which is permitted by the constraints from CMB and 21-cm absorption. A very small relic fraction of is compatible with the stringent bounds on un-boosted -electron scattering in DM direct detection, and the -electron scattering is also allowed.