Solar $\gamma$-rays as a Complementary Probe of Dark Matter

We show that observations of solar $\gamma$-rays offer a novel probe of dark matter in scenarios where interactions with the visible sector proceed via a long-lived mediator. As a proof of principle, we demonstrate that there exists a class of models which yield solar $\gamma$-ray fluxes observable with the next generation of $\gamma$-ray telescopes, while being allowed by a variety of current experimental constraints. The parameter space allowed by big bang nucleosynthesis and beam dump experiments naturally leads to mediator lifetimes sufficient to produce observable solar $\gamma$-ray signals. The model allows for solar $\gamma$-ray fluxes up to orders of magnitude larger compared to dwarf spheroidal galaxies, without reaching equilibrium between dark matter annihilation and capture rate. Our results suggest that solar $\gamma$-ray observations are complementary, and in some cases superior, to existing and future dark matter detection efforts.