Minimal Majoron dark matter

A bstract We study Majoron dark matter (DM) in its minimal realization, based on the Type-I seesaw framework extended by a SM-singlet complex scalar. Remaining agnostic about the origin and value of the Majoron mass, we evaluate the DM abundance from both the freeze-in and misalignment mechanisms, and identify the viable parameter space consistent with observational constraints. Without fine-tuning of the initial misalignment angle, we find that the Majoron mass is bounded by mJ O(10) m J ≲ O 10 MeV. We also discuss compatibility with thermal leptogenesis. Successful leptogenesis with two right-handed neutrinos favors misalignment-dominated production with the Majoron mass mJ O(100) m J ≲ O 100 eV, while freeze-in dominated production is compatible with leptogenesis only with a mild fine-tuning of the initial misalignment angle, θᵢ O(0.01) θ i ≲ O 0.01 .