XENON1T excess in local Z2 DM models with light dark sector
Seungwon Baek, Jong‐Kuk Kim, Pyungwon Ko
Abstract
Recently XENON1T Collaboration announced that they observed some excess in the electron recoil energy around a 2–3 keV. We show that this excess can be interpreted as exothermic scattering of excited dark matter on atomic electron through dark photon exchange. We consider DM models with local dark U(1) gauge symmetry that is spontaneously broken into its Z2 subgroup by Krauss-Wilczek mechanism. In order to explain the XENON1T excess with the correct DM thermal relic density within freeze-out scenario, all the particles in the dark sector should be light enough, namely ∼O(100) MeV for scalar DM and ∼O(1−10) MeV for fermion DM cases. And even lighter dark Higgs ϕ plays an important role in the DM relic density calculation: XX†→Z′ϕ for scalar DM (X) and χχ¯→ϕϕ for fermion DM (χ) assuming mZ′>mχ. Both of them are in the p-wave annihilation, and one can easily evade stringent bounds from Planck data on CMB on the s-wave annihilations, assuming other dangerous s-wave annihilations are kinematically forbidden.