Dark matter from the centre of SU(N)

Abstract

A dark sector with non-abelian gauge symmetry provides a sound framework to justify stable dark matter (DM) candidates. We consider scalar fields charged under a SU(N)SU(N) gauge group, and show that the centre of SU(N)SU(N), the discrete subgroup Z_NZN also known as NN-ality, can ensure the stability of scalar DM particles. We analyse in some details two minimal DM models of this class, based on SU(2)SU(2) and SU(3)SU(3), respectively. These models have non-trivial patterns of spontaneous symmetry breaking, leading to distinctive phenomenological implications. For the SU(2)SU(2) model these include a specific interplay of two DM states, with the same interactions but different masses, and several complementary DM annihilation regimes, either within the dark sector or through the Higgs portal. The SU(3)SU(3) model predicts dark radiation made of a pair of dark photons with a unique gauge coupling, as well as regimes where DM semi-annihilations become dominant and testable.