Semi-annihilating dark matter coupled with Majorons

Abstract

The thermal production mechanism of dark matter is attractive and wellmotivated by predictivity. A representative of this type of dark matter candidate is the canonical, weakly interacting massive particles. An alternative is semiannihilating dark matter, which exhibits different phenomenological aspects from the former example. In this study, we constructed a model of dark matter semiannihilating into a pair of anti-dark matter and a Majoron based on a global U (1) B−L symmetry, and show that semi-annihilation induces the core formation of dark matter halos, which can alleviate the so-called small-scale problems. In addition, the box-shaped spectrum of neutrinos was produced by the subsequent decay of the Majoron. This can be a distinctive signature of the dark matter in the model. We find a parameter space where the produced neutrinos can be detected by the future large-volume neutrino detector Hyper-Kamiokande. We also compared the dark matter scenario with the case of halo core formation by the strongly self-interacting dark matter.