Solar capture and annihilation of fermionic and scalar dark matter motivated by the LUX-ZEPLIN high-recoil candidate

Abstract

Motivated by the LUX-ZEPLIN high-energy nuclear-recoil candidate, we ask whether solar evolution can distinguish dark-matter models that are degenerate in their leading xenon recoil response. We compare a split fermionic electroweak doublet with a specified inert scalar doublet, matching their masses, excitation energy, coherent transition interaction, and leading elastic nuclear response. This matching fixes the same direct-detection signal and the same optically thin first-capture source in the Sun, while leaving post-capture dynamics model dependent. We follow finite-temperature capture, orbital evolution, scattering, excited-state decay, escape, thermal entry, and annihilation. The different excited-state lifetimes generate distinct capture histories, but, for the specified cooling interaction, both retained populations thermalize and reach capture--annihilation equilibrium, yielding only a modest difference in their late annihilation rates. We also derive an analytic protected-capture criterion and test the result against shared halo, solar-composition, and nuclear-response variations. Although the total annihilation rates remain similar, model-dependent gauge-boson branching fractions and polarizations produce distinct neutrino spectra at production. A source-level comparison with published IceCube templates shows that the nominal partial $WW$ sources exceed the corresponding pure-$WW$ template limits, without constituting a detector-level exclusion or model discrimination. Solar evolution therefore provides a complementary probe of particle-model differences hidden by a matched xenon signal.