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, hd, responsible for generating the mass of the dark photon, γd. We show that the condition mhd≤mγd, together with smallness of the kinetic mixing parameter, ϵ, and/or dark gauge coupling, gd, 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→{γd,hd}, and freeze-out, {γd,hd}→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.