Gravity-Higgs portal for dark matter decay

Abstract Dark matter can decay via gravity portals and contribute a minor decay (MD) width. This paper studies a non-minimal coupling between the Higgs field and gravity, which lead to additional gravity-Higgs portals for gravitational dark matter to decay and contribute additional decay (AD) width. Characterizing AD-induced signals is crucial, as it provides theoretical templates for future space-borne detectors to search for dark matter decay signatures in cosmic rays and identify their potential contributions. For scalar dark matter candidates with a mass less than 5 TeV, the decay branching ratios are almost independent of whether dark matter decay through gravity portals or gravity-Higgs portals; therefore, it is almost impossible to distinguish gravity portals from gravity-Higgs portals by observing decay products. For fermionic singlet dark matter candidates, their MD products are diverse, while their AD products are monotonous, mostly neutrinos and Higgs bosons. For both dark matter candidates, gravity-Higgs portals tend to govern decays when their mass is in the several hundred GeV range.