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This paper shows that the Sun can rule out a region of parameter space for Higgsino dark matter, a well-motivated particle candidate. The authors calculate how Higgsinos that scatter inelastically inside the Sun can be captured and then annihilate to produce high-energy neutrinos. Comparing the predicted neutrino signal for a Higgsino mass of about 1.08 tera-electronvolts (TeV) with ten years of IceCube non-detections leads to a robust lower limit on the Higgsino mass splitting: δ > 566 kilo-electronvolts (keV). That bound also rules out an explanation of a recent LZ detector event as Higgsinos scattering on xenon nuclei.
What the researchers did. They treated the Higgsino as a “quasi-Dirac” particle made of two nearly degenerate Majorana states. The energy gap between these states, called the mass splitting δ, controls whether a dark matter particle can scatter off a nucleus by jumping up in mass (an inelastic process). The team fixed the Higgsino mass to the cosmologically preferred value of 1.08 TeV and varied δ. They computed how many dark matter particles the Sun should capture by modeling the incoming dark matter speeds, the solar density profile, and nuclear scattering on heavy elements such as iron and uranium.
How the idea works in plain language. Dark matter in the Galaxy is usually too slow for some kinds of inelastic collisions on Earth. But the Sun’s gravity accelerates incoming particles to much higher speeds—up to roughly 1,400 kilometers per second in the core—so collisions that are impossible on Earth can happen in the Sun. If a Higgsino loses enough energy in a collision it becomes bound to the Sun. Captured Higgsinos sink toward the center and eventually meet and annihilate into Standard Model particles like W and Z bosons. Those decays produce high-energy neutrinos that can escape the Sun and be searched for by neutrino telescopes such as IceCube.
Key results and why they matter. Using a solar capture calculation and published IceCube limits, the authors infer that the annihilation rate into W+W− for a 1.08 TeV Higgsino must be below about 1.5×10^19 per second at Earth. Translating that into the allowed mass-splitting range gives the lower bound δ > 566 keV. This is a stronger constraint than what terrestrial xenon detectors can probe, because the Sun’s higher speeds and heavy elements extend sensitivity to larger splittings. The new bound therefore excludes interpreting the recent high-recoil LZ event as endothermic (energy-absorbing) Higgsino scattering on xenon.
Important caveats. The limit assumes that captured Higgsinos thermalize and concentrate near the solar center so that annihilation reaches equilibrium with capture. The authors note that equilibrium is achieved only if the typical radius of the captured Higgsino population is small enough (they use a reference radius of about 0.017 solar radii). The result also depends on assumptions about the annihilation rate, the Sun’s heavy-element distribution, nuclear form factors used in the scattering calculation, and IceCube’s neutrino-analysis assumptions. If these conditions fail—if captured particles do not sink and thermalize, or if the annihilation rate is much smaller—then the derived bound on δ would be weaker. The authors present their limit as robust under their stated assumptions but not immune to these model and astrophysical uncertainties.