Gamma-Ray Signatures of Thermal Misalignment Dark Matter

Thermal misalignment is a viable dark matter scenario where the misalignment of a dark matter scalar, feebly coupled to the Standard Model particles, is generated through thermal effects from the primordial plasma. In this framework, the scalar is generically metastable, and its decay can leave observable signatures. In this work, we focus on the case in which the scalar $\phi$ is coupled to photons through $\phi F^{\mu\nu} F_{\mu\nu}$, and examine its observational signatures. We find that current gamma-ray constraints place a robust upper bound on the scalar mass of $\mathcal O(1)\,\mathrm{GeV}$. We also find that future observations can further probe the parameter region, particularly in the MeV--GeV range, an energy band expected to be explored by various gamma-ray observatories in the coming decades.