Testing Higgs-Coupled Minimal Dark Matter with Solar Neutrinos after the LZ High-Recoil Event

RESUMO

The LUX-ZEPLIN (LZ) Collaboration has reported a nuclear-recoil candidate at $248$ keV, motivating interpretations in terms of endothermic dark matter (DM). We investigate this signal in Higgs-coupled minimal dark matter (HC-MDM), where the same electroweak interaction responsible for the terrestrial recoil also induces DM capture in the Sun and a potentially observable high-energy neutrino signal. We independently determine the mass splittings required to reproduce the LZ event and perform an improved calculation of Solar capture and post-capture evolution. Our treatment includes natural isotope mixtures, exact inelastic kinematics, nuclear form factors, finite-temperature nuclear motion near kinematic closure, orbital cooling through loop-induced elastic scattering, and an explicit capture--annihilation equilibrium test. The resulting Solar predictions are numerically stable and robust against the astrophysical and nuclear variations considered. For the two thermal benchmarks within the released IceCube DM mass grid, $3_M2_D$ and $5_M4_D$, the predicted annihilation rates exceed the mass-matched $W^+W^-$ IceCube response by factors of approximately $2.2\times10^3$ and $91$, placing both standard-halo solutions under strong tension within the $W^+W^-$ response mapping used here. For the heavier representations, whose masses lie above the published $10$ TeV IceCube grid, we construct a response-based extrapolation to higher masses. The $22$ TeV $7_M6_D$ benchmark remains in strong tension with IceCube even under our conservative response-loss extrapolation, while the $48$ TeV $9_M8_D$ benchmark also remains above the extrapolated response, although much closer to the sensitivity boundary. The $82$ TeV $11_M10_D$ benchmark is response dependent, whereas the $130$ TeV $13_M12_D$ benchmark remains below the extrapolated IceCube sensitivity.