Solar Capture and Suppressed Annihilation of Inelastic Scalar Dark Matter

Abstract

Solar capture of inelastic dark matter need not imply a large annihilation signal. We demonstrate this in a scalar low-energy model with a $B-3L_τ$ current, motivated by the high-energy recoil candidate reported by LUX-ZEPLIN. For a benchmark with $m_χ= 840~\mathrm{GeV}$, a mass splitting of $320~\mathrm{keV}$, and a $160~\mathrm{MeV}$ mediator, a reconstruction using the public LZ response gives 0.965 accepted events, while the relic abundance is $Ωh^2 \simeq 0.120$. Finite-momentum nuclear responses preserve substantial capture on iron despite the strong suppression of its coherent charge at zero momentum transfer. Following the captured particles through their orbital evolution, including thermal nuclear motion, elastic and inelastic scattering, and excited-state decay, we find an extended dark-matter population with $r_{\rm eff}=0.215R_\odot$. Although same-state annihilation channels remain open, the corresponding annihilation estimate is only 0.0404 of the public IceCube $W^+W^-$-calibrated proxy, a factor of 628 below the corresponding isothermal estimate. Thus substantial solar capture can coexist with a strongly suppressed neutrino signal.