Strong Constraints on Higgsino Dark Matter from Solar Capture

Higgsino dark matter remains one of the most convincing dark matter candidates. It can exist in a ``quasi-Dirac" regime, when the splitting between two Majorana components is on the order of O(few,MeV) or less. Owing to the strong gravitational pull of the Sun, the DM particles accelerate to up to about 1400,km/sec in the solar core, which allows for inelastic scattering on heavy elements and very effective capture onto solar-bound trajectories. We evaluate the expected flux of the neutrinos from the expected χχ to W+W-,ZZ annihilation for the cosmologically preferred mass, m χ 1.08,TeV while keeping the mass splitting δ as a free parameter. Confronting it with the non-observation of high-energy neutrinos from the Sun by the IceCube experiment, we obtain a robust limit, δ>566,keV. These limits exclude the interpretation of the recent LZ event in terms of endothermic inelastic scattering of Higgsino dark matter on xenon nuclei.