Higgsino Dark Matter Interpretation of the LZ High-Recoil Event in the GNMSSM with TeV-Scale Gauginos

Abstract

The nuclear recoil event at approximately 248 keV reported by the LUX-ZEPLIN collaboration motivates an investigation of endothermic dark matter scattering. We study this within the General Next-to-Minimal Supersymmetric Standard Model (GNMSSM), with Higgsino-dominated neutralino DM undergoing the $Z$-mediated transition $\widetildeχ_1^0N\to\widetildeχ_2^0N$. In the conventional thermal Higgsino limit of the MSSM, the observed relic abundance selects a mass near 1.1 TeV, while a neutralino splitting of a few hundred keV typically requires gaugino masses of order $10^7$ GeV. In the GNMSSM, Higgsino-Singlino mixing introduces an additional contribution to the splitting that can cancel the gaugino-induced contribution, allowing sub-MeV splitting with multi-TeV gauginos. This mixing also modifies the inelastic scattering coupling and annihilation rates, while coannihilation with sleptons provides freedom in obtaining the observed relic abundance. We present six benchmark points with dark-matter masses of 0.66-1.11 TeV, neutralino splittings of 333-350 keV, and gaugino masses of 2-5 TeV. These points reproduce the observed relic abundance and satisfy direct-detection, Higgs, flavor, and collider constraints. Within the Standard Halo Model and extended-likelihood analysis, all six points yield $Δχ^2<1$ relative to the best fit. Our results show how the GNMSSM can accommodate the LZ high-recoil event without an ultraheavy gaugino sector. A quantitative assessment of solar-capture and neutrino-telescope constraints remains necessary for establishing viability.