Dark photons from captured inelastic dark matter annihilation: Charged particle signatures

The dark sector may contain a dark photon that kinetically mixes with the Standard Model photon, allowing dark matter to interact weakly with normal matter. In previous work we analyzed the implications of this scenario for dark matter capture by the Sun. Dark matter will gather in the core of the Sun and annihilate to dark photons. These dark photons travel outwards from the center of the Sun and may decay to produce positrons that can be detected by the Alpha Magnetic Spectrometer (AMS-02) on the International Space Station. We found that the dark photon parameter space accessible to this analysis is largely constrained by strong limits on the spin-independent weakly interacting massive particle-nucleon cross section from direct detection experiments. In this paper we build upon previous work by considering the case where the dark sector contains two species of Dirac fermion that are nearly degenerate in mass and couple inelastically to the dark photon. We find that for small values of the mass splitting Delta similar to 100 keV, the predicted positron signal at AMS-02 remains largely unchanged from the previously considered elastic case, while constraints from direct detection are relaxed. As such, there remains a region of parameter space with dark matter mass 100 GeV less than or similar to m(X) less than or similar to 10 TeV, dark photon mass 1 MeV less than or similar to m(A') less than or similar to 100 MeV, and kinetic mixing parameter 10(-9) less than or similar to epsilon less than or similar to 10(-8) that is untouched by supernova observations and fixed target experiments but where an inelastic dark sector may still be discovered using existing AMS-02 data.