Inelastic Dark Photon Dark Matter for the LUX-ZEPLIN High-Recoil Event and the Galactic Halo Gamma-Ray Excess

We show that a dark-photon dark matter framework can simultaneously account for two recently reported anomalies: the halo-like Galactic gamma-ray excess identified by Totani in 15 years of Fermi-LAT data, and the E nr=248 plus or minus23,(stat) plus or minus23,(sys) keV nuclear-recoil event of interest reported by the LUX-ZEPLIN Collaboration. The dark matter is a U(1) X dark photon X with mass m X=420 GeV, stabilized by a dark parity that forbids kinetic mixing with the Standard Model photon. A light scalar mediator ϕ, required to explain the Totani excess via Sommerfeld enhancement, is joined by a second light scalar ϕ' that couples a nearly degenerate heavier vector partner V to X. The resulting inelastic transition X+N to V+N, with mass splitting δ 316 keV close to the kinematic endpoint for m X=420 GeV, naturally reproduces the localized LZ event once the detector energy resolution is included, while leaving the relic abundance and the halo phenomenology of the original Totani-motivated benchmark essentially unchanged.