Interpretation of XENON1T excess with MeV boosted dark matter

The XENON IT 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,SAand SB,to interpret the XENON IT keV excess via boosted SB.A small mass splitting mSA-mSB>0 is introduced,and the boosted SBcan be produced using the dark annihilation process of SASA~→φ→SBSB~ via a resonant scalar φ.SB-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 X-mediated SB-electron scattering cross section to be≤10-35cm~2,the MeV scale DM with a resonance enhanced dark annihilation today can still provide sufficient boosted SBand induce the XENON1 T keV excess.The relic density of SBis significantly reduced by the s-wave process SBSB~→XX,which is permitted by the constraints from CMB and 21-cm absorption.A very small relic fraction of SBis compatible with the stringent bounds on un-boosted SB-electron scattering in DM direct detection,and the SA-electron scattering is also allowed.