Dark Higgs dark matter

A new U (1 ) "dark" gauge group coupled to the Standard Model (SM) via the kinetic mixing portal provides a dark matter candidate in the form of the Higgs field, h_d, responsible for generating the mass of the dark photon, γ_d. We show that the condition m_hd≤m_γd , together with smallness of the kinetic mixing parameter, ε , and/or dark gauge coupling, g_d, leads the dark Higgs to be sufficiently metastable to constitute dark matter. We analyze the Universe's thermal history and show that both freeze-in, SM →{γ_d,h_d}, and freeze-out, {γ_d,h_d}→SM , processes can lead to viable dark Higgs dark matter with a sub-GeV mass and a kinetic mixing parameter in the range 10^-13≲ε ≲10^-6 . Observable signals in astrophysics and cosmology include modifications to primordial elemental abundances, altered energetics of supernovae explosions, dark Higgs decays in the late Universe, and dark matter self-interactions.