Explain the LZ High-Energy Recoil Event with Inelastic Sneutrino Dark Matter in Supersymmetry

Abstract

We investigate inelastic sneutrino dark matter in the inverse-seesaw extension of the next-to-minimal supersymmetric standard model as an explanation of the high-energy nuclear-recoil candidate reported by LUX-ZEPLIN (LZ). Approximate lepton-number conservation protects the small sneutrino mass splitting, while a left-handed admixture permits an observable inelastic signal with suppressed elastic scattering. Three mechanisms can suppress the solar dark-matter neutrino signal while preserving the thermal relic abundance: annihilation into singlet pseudoscalars with predominantly diphoton decays, thermally enhanced annihilation near a Higgs resonance, and electroweakino coannihilation. We calculate the recoil spectra and confront representative benchmarks with solar-neutrino searches and Fermi-LAT gamma-ray constraints. These experiments stringently constrain the benchmarks, yet we identify points consistent with all the constraints from dark matter, Higgs, and flavour physics considered here. A three-generation neutrino-sector completion can also reproduce the measured neutrino oscillation observables. These results support the viability of the sneutrino interpretation of the LZ event and establish complementary direct and indirect tests of such a supersymmetric model.