📝 SummarXiv

Abstract

Dark matter (DM) particles traversing the Sun can lose energy through elastic scattering with solar nuclei and become gravitationally captured. For DM with masses below a few GeV, however, evaporation caused by collisions with hot nuclei efficiently ejects particles, preventing their long-term accumulation. This defines a minimum mass threshold, typically around a few GeV, below which the Sun cannot retain DM. In this work, we investigate how an additional evaporation barrier - arising either from multiple scattering in an optically thick regime or from a long-range DM-nucleon interaction - modifies this equilibrium. We compute the transport and thermalization of captured DM using a phase-space approach that evolves the orbital distribution rather than assuming a Maxwellian form. Without a barrier, we recover the standard result that evaporation dominates for sub-few-GeV DM, leading to negligible net retention. With a barrier, however, the escape of light DM is strongly suppressed, enabling the Sun to capture and retain particles below the canonical evaporation mass. The barrier effectively raises the escape threshold, either through repeated scatterings or through an additional long-range attractive potential. We present the resulting phase-space distributions, density and velocity profiles, and highlight how the suppression of the high-velocity tail drives the captured population closer to thermal equilibrium with the solar core. These modifications increase the equilibrium abundance of light DM by orders of magnitude and have direct implications for solar neutrino searches as an indirect probe of DM.