Can Nuclear Recoils and Solar Neutrinos Resolve the Composition of Singlino-Higgsino Dark Matter?

Abstract: A nuclear recoil measures dark matter (DM) scattering on nucleons, but usually cannot reveal the nature of the halo DM. An interchange of the ground and excited states of the DM can preserve an inelastic recoil spectrum while changing ground-state annihilation by several orders of magnitude. Solar neutrinos can then provide information that nuclear recoils leave unresolved. Motivated by the high-energy LUX-ZEPLIN candidate, we investigate a possible way to resolve the composition of singlino-Higgsino DM in the next-to-minimal supersymmetric standard model (NMSSM) by using nuclear recoils and solar neutrinos. Our analysis identifies solar-compatible singlino ground states and Higgsino ground states with weak inelastic transitions, whereas Higgsino-pair inelastic LZ fits predict excessive solar signals. An elastic Higgsino scattering alternative can suppress solar capture by closing the inelastic transition. Recoil spectra, solar evolution and target complementarity can therefore probe distinct aspects of the singlino-Higgsino DM composition, with residual degeneracies set by annihilation, halo and detector assumptions.