Search

Dark photons in the MeV to GeV mass range are important targets for experimental searches. We consider the case where dark photons A' decay invisibly to hidden dark matter X through A' → XX. For generic masses, proposed accelerator searches are projected to probe the thermal target region of parameter space, where the X particles annihilate through XX → A' → SM in the early universe and freeze out with the correct relic density. However, if mA' ≈ 2mX, dark matter annihilation is resonantly enhanced, shifting the thermal target region to weaker couplings. For ~10 % degeneracies, we find that the annihilation cross section is generically enhanced by 4 (2) orders of magnitude for scalar (pseudo-Dirac) dark matter. For such moderate degeneracies, the thermal target region drops to weak couplings beyond the reach of all proposed accelerator experiments in the scalar case and becomes extremely challenging in the pseudo-Dirac case. Proposed direct detection experiments can probe moderate degeneracies in the scalar case. For greater degeneracies, the effect of the resonance can be even more significant, and both scalar and pseudo-Dirac cases are beyond the reach of all proposed accelerator and direct detection experiments. For scalar dark matter, we find an absolute minimum that sets the ultimate experimental sensitivity required to probe the entire thermal target parameter space, but for pseudo-Dirac fermions, we find no such thermal target floor. [ABSTRACT FROM AUTHOR]

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 Δ~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≲mX≲10 TeV, dark photon mass 1 MeV≲mA'≲100 MeV, and kinetic mixing parameter 10-9≲ϵ≲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. [ABSTRACT FROM AUTHOR]