Dark matter semi-annihilation for inert scalar multiplets

Dark matter semi-annihilation is a process through which two dark matter candidates annihilate to a single dark matter particle and a non-dark matter particle. Such processes are common when the symmetry stabilizing the dark matter differs from ℤ2 and can lead to qualitatively different phenomenology. In this work, we study the viability of semi-annihilation models including one or two inert multiplets. For one multiplet, we show that there does not exist any viable model in which semi-annihilation is efficient. For two multiplets, semi-annihilation can be efficient, but the number of viable and technically natural models is limited. We then perform a detailed study of the most promising model, showing that the correct relic abundance can be obtained for a wide range of masses.