Interacting scalar-fermion two-component dark matter in a gauged $\boldsymbol{U(1)_{B-L}}$ model

Abstract

We propose an interacting two-component dark matter model based on a gauged $U(1)_{B-L}$ extension of the Standard Model, which also accommodates neutrino masses through the type-I seesaw mechanism. The dark sector consists of a Dirac fermion $\chi$ and a complex scalar $S$, which can both be stable without imposing an additional discrete symmetry and are directly coupled by a gauge-invariant Yukawa interaction. The resulting conversion, semi-conversion, and semi-annihilation processes lead to a genuinely coupled freeze-out. After imposing collider and dark matter constraints, we identify viable solutions away from the $Z'$ resonance for both mass hierarchies, $m_S>m_\chi$ and $m_S<m_\chi$. Despite the strong direct-detection constraints, part of the surviving parameter space remains within the reach of next-generation experiments.