Semi-annihilating $Z_3$ Dark Matter for XENON1T Excess

Understand

The recently reported result from XENON1T experiment indicates that there is an excess with $3.5\sigma$ significance in the electronic recoil events.

• Interpreted as new physics, new sources are needed to account for the electronic scattering.
• We show that a dark fermion $\psi$ with mass about $ \mathcal{O}\left(10\right)$ MeV from semi-annihilation of $Z_3$ dark matter $X$ and subsequent decay of a dark gauge boson $V_\mu$ may be responsible for the excess.
• The relevant semi-annihilation process is $X+X\rightarrow \overline{X}+V_\mu (\rightarrow \psi + \overline{\psi})$, in which the final $\psi$ has a box-shape energy spectrum.