Non-Abelian dark matter: Models and constraints

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Numerous experimental anomalies hint at the existence of a dark matter (DM) multiplet ${\ensuremath{\chi}}_{i}$ with small mass splittings. We survey the simplest such models which arise from DM in the low representations of a new SU(2) gauge symmetry, whose gauge bosons have a small mass $\ensuremath{\mu}\ensuremath{\lesssim}1\text{ }\text{ }\mathrm{GeV}$. We identify preferred parameters ${M}_{\ensuremath{\chi}}\ensuremath{\cong}1\text{ }\text{ }\mathrm{TeV}$, $\ensuremath{\mu}\ensuremath{\sim}100\text{ }\text{ }\mathrm{MeV}$, ${\ensuremath{\alpha}}_{g}\ensuremath{\sim}0.04$, and the $\ensuremath{\chi}\ensuremath{\chi}\ensuremath{\rightarrow}4e$ annihilation channel, for explaining PAMELA, Fermi, and INTEGRAL/SPI lepton excesses, while remaining consistent with constraints from relic density, diffuse gamma rays, and the CMB. This consistency is strengthened if DM annihilations occur mainly in subhalos, while excitations (relevant to the excited DM proposal to explain the 511 keV excess) occur in the galactic center, due to higher velocity dispersions in the galactic center, induced by baryons. We derive new constraints and predictions which are generic to these models. Notably, decays of excited DM states ${\ensuremath{\chi}}^{\ensuremath{'}}\ensuremath{\rightarrow}\ensuremath{\chi}\ensuremath{\gamma}$ arise at one loop and could provide a new signal for INTEGRAL/SPI; big bang nucleosynthesis constraints on the density of dark SU(2) gauge bosons imply a lower bound on the mixing parameter $ϵ$ between the SU(2) gauge bosons and photon. These considerations rule out the possibility of the gauge bosons that decay into ${e}^{+}{e}^{\ensuremath{-}}$ being long-lived. We study in detail models of doublet, triplet, and quintuplet DM, showing that both normal and inverted mass hierarchies can occur, with mass splittings that can be parametrically smaller [e.g., $O(100)\text{ }\text{ }\mathrm{keV}$] than the generic MeV scale of splittings. A systematic treatment of ${Z}_{2}$ symmetry, which insures the stability of the intermediate DM state, is given for cases with inverted mass hierarchy, of interest for boosting the 511 keV signal from the excited dark matter mechanism.