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We study the effect of a first-order phase transition in a confining $SU(N)$ dark sector with heavy dark quarks. The baryons of this sector are the dark matter candidate. During the confinement phase transition the heavy quarks are trapped inside isolated, contracting pockets of the deconfined phase, giving rise to a second stage of annihilation that dramatically suppresses the dark quark abundance. The surviving abundance is determined by the local accidental asymmetry in each pocket. The correct dark matter abundance is obtained for $mathcal{O}(1-100)$ PeV dark quarks, above the usual unitarity bound.
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Very light dark matter is usually taken to consist of uncharged bosons such as axion-like particles or dark photons. Here, we consider the prospect of very light, possibly even sub-eV dark matter carrying a net charge that is (approximately) conserved. By making use of the Affleck-Dine mechanism for its production, we show that a sizable fraction of the energy density can be stored in the asymmetric component. We furthermore argue that there exist regions of parameter space where the energy density contained in symmetric particle-antiparticle pairs without net charge can to some degree be depleted by considering couplings to additional fields. Finally, we make an initial foray into the phenomenology of this scenario by considering the possibility that dark matter is coupled to the visible sector via the Higgs portal.
We propose a scenario that the Electroweak-Skyrmion, a solitonic object made of the Higgs field and the electroweak gauge fields, is identified as an asymmetric dark matter. In this scenario, the relic abundance of the dark matter is related to the baryon asymmetry of the Universe through a sphaleron-like process. We show that the observed ratio of dark matter abundance to the baryon asymmetry can be explained by this scenario with an appropriate choice of model parameters that is allowed by currently available experimental constraints.
It is often said that asymmetric dark matter is light compared to typical weakly interacting massive particles. Here we point out a simple scheme with a neutrino portal and $mathcal{O}(60 text{ GeV})$ asymmetric dark matter which may be added to any standard baryogenesis scenario. The dark sector contains a copy of the Standard Model gauge group, as well as (at least) one matter family, Higgs, and right-handed neutrino. After baryogenesis, some lepton asymmetry is transferred to the dark sector through the neutrino portal where dark sphalerons convert it into a dark baryon asymmetry. Dark hadrons form asymmetric dark matter and may be directly detected due to the vector portal. Surprisingly, even dark anti-neutrons may be directly detected if they have a sizeable electric dipole moment. The dark photons visibly decay at current and future experiments which probe complementary parameter space to dark matter direct detection searches. Exotic Higgs decays are excellent signals at future $e^+ e^-$ Higgs factories.
It has been argued that the existence of old neutron stars excludes the possibility of non-annihilating light bosonic dark matter, such as that arising in asymmetric dark matter scenarios. If non-annihilating dark matter is captured by neutron stars, the density will eventually become sufficient for black hole formation. However, the dynamics of collapse is highly sensitive to dark-matter self-interactions. Repulsive self-interactions, even if extremely weak, can prevent black hole formation. We argue that self-interactions will necessarily be present, and estimate their strength in representative models. We also consider co-annihilation of dark matter with nucleons, which arises naturally in many asymmetric dark matter models, and which again acts to prevent black hole formation. We demonstrate how the excluded region of the dark-matter parameter space shrinks as the strength of such interactions is increased, and conclude that neutron star observations do not exclude most realistic bosonic asymmetric dark matter models.
The asymmetric dark matter (ADM) scenario can solve the coincidence problem between the baryon and the dark matter (DM) abundance when the DM mass is of ${cal O}(1),$GeV. In the ADM scenarios, composite dark matter is particularly motivated, as it can naturally provide the DM mass in the ${cal O}(1),$GeV range and a large annihilation cross section simultaneously. In this paper, we discuss the indirect detection constraints on the composite ADM model. The portal operators connecting the $B-L$ asymmetries in the dark and the Standard Model(SM) sectors are assumed to be generated in association with the seesaw mechanism. In this model, composite dark matter inevitably obtains a tiny Majorana mass which induces a pair-annihilation of ADM at late times. We show that the model can be efficiently tested by the searches for the $gamma$-ray from the dwarf spheroidal galaxies and the interstellar electron/positron flux.
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