Interpretation of XENON1T excess with MeV boosted dark matter

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, \begin{document}$ S_A $\end{document} and \begin{document}$ S_B $\end{document}, to interpret the XENON1T keV excess via boosted \begin{document}$ S_B $\end{document}. A small mass splitting \begin{document}$ m_{S_A}-m_{S_B}>0 $\end{document} is introduced, and the boosted \begin{document}$ S_B $\end{document} can be produced using the dark annihilation process of \begin{document}$ S_A S_A^\dagger \to \phi \to S_B S_B^\dagger $\end{document} via a resonant scalar ?. \begin{document}$ S_B- $\end{document}electron scattering is intermediated by a vector boson X. Although the constraints from Big Bang nucleosynthesis, cosmic microwave background (CMB), and low-energy experiments set the \begin{document}$ X- $\end{document}mediated \begin{document}$ S_B- $\end{document}electron scattering cross section to be \begin{document}$ \lesssim 10^{-35} \mathrm{cm}^2 $\end{document}, the MeV scale DM with a resonance enhanced dark annihilation today can still provide sufficient boosted \begin{document}$ S_B $\end{document} and induce the XENON1T keV excess. The relic density of \begin{document}$ S_B $\end{document} is significantly reduced by the s-wave process \begin{document}$ S_B S_B^\dagger \to X X $\end{document}, which is permitted by the constraints from CMB and 21-cm absorption. A very small relic fraction of \begin{document}$ S_B $\end{document} is compatible with the stringent bounds on un-boosted \begin{document}$ S_B $\end{document}-electron scattering in DM direct detection, and the \begin{document}$ S_A $\end{document}-electron scattering is also allowed.