Heavy fermionic dark matter in a secluded $Z_4$ framework

Abstract

We investigate heavy Majorana dark matter $\chi$ in a secluded scalar sector with a spontaneously broken $Z_4$ symmetry. The symmetry forbids a bare Majorana mass, providing a dynamical origin for the dark matter mass, while a residual $Z_2$ symmetry ensures its stability. We find that the thermal relic abundance can be predominantly determined by the secluded annihilation process $\chi \chi \to h_2{h}_2$ , where $h_2$ is the new heavy Higgs boson. The dominant annihilation process is p-wave suppressed at low velocities, leading to a strong suppression of the present-day annihilation rate relative to that at freeze-out. Consequently, the model can accommodate a heavy thermal dark matter candidate with highly suppressed indirect-detection signals while retaining potentially testable signatures in direct-detection experiments.