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.