Non-Thermal Production of Sexaquark Dark Matter

Abstract

Standard thermal freeze-out scenarios with QCD-scale interaction rates predict a $uuddss$ sexaquark relic abundance many orders of magnitude below the observed dark matter density, representing a key challenge for sexaquark dark matter models. Additionally, if the maximum post-inflationary temperature never exceeds the QCD confinement scale, the usual thermal/chemical-equilibrium production of the sexaquark near $T \sim T_{\rm QCD} \simeq 150 - 170$ MeV never occurs. In this work we show that non-thermal mechanisms can naturally overcome this obstacle. Using late-decaying reheatons as a representative case (while noting the broader applicability), we demonstrate that the final abundance is determined by two quantities: the branching fraction into strange-quark-rich matter and the coalescence probability into sexaquarks during the matter-dominated or early radiation-dominated epoch. We provide compact expressions and benchmark calculations for reheating temperatures $T_R \in [10, 100]$ MeV and reheaton masses above the QCD confinement scale. Unlike the predictive but unsuccessful thermal scenario, non-thermal production is sensitive to injection microphysics, coalescence efficiency, and residual entropy dilution. We delineate the viable parameter space, evaluate collider and precision constraints on representative reheaton models, and derive indirect detection bounds on residual antisexaquark populations. Our results establish non-thermal production as a viable pathway to sexaquark dark matter and highlight broader implications for non-equilibrium mechanisms in the early universe.