Comprehensive asymmetric dark matter model

Abstract

Asymmetric dark matter (ADM) is motivated by the similar cosmological mass densities measured for ordinary and dark matter. We present a comprehensive theory for ADM that addresses the mass density similarity, going beyond the usual ADM explanations of similar number densities. It features an explicit matter-antimatter asymmetry generation mechanism, has one fully worked out thermal history and suggestions for other possibilities, and meets all phenomenological, cosmological and astrophysical constraints. Importantly, it incorporates a deep reason for why the dark matter mass scale is related to the proton mass, a key consideration in ADM models. Our starting point is the idea of mirror matter, which offers an explanation for dark matter by duplicating the standard model with a dark sector related by a Z 2 parity symmetry. However, the dark sector need not manifest as a symmetric copy of the standard model in the present day. By utilizing the mechanism of "asymmetric symmetry breaking" with two Higgs doublets in each sector, we develop a model of ADM where the mirror symmetry is spontaneously broken, leading to an electroweak scale in the dark sector that is significantly larger than that of the visible sector. The weak sensitivity of the ordinary and dark QCD confinement scales to their respective electroweak scales leads to the necessary connection between the dark matter and proton masses. The dark matter is composed of either dark neutrons or a mixture of dark neutrons and metastable dark hydrogen atoms. Lepton asymmetries are generated by the CP-violating decays of heavy Majorana neutrinos in both sectors. These are then converted by sphaleron processes to produce the observed ratio of visible to dark matter in the universe. The dynamics responsible for the kinetic decoupling of the two sectors emerges as an important issue that we only partially solve.

Dark matter bound states via emission of scalar mediators

“…1, the phase-space encompassed by eq. (3.43) extends on the x a´xb plane essentially along the line 44) with 0 ď x a ď ? 1´2d, and a small width along the x b direction, due to cos θ ab ranging in r´1, 1s.…”

“…While the importance of bound-state formation (BSF) for DM is now well established for weakly coupled theories with vector mediators [5-13, 16-18, 30-39], and of course in confining DM theories [40][41][42][43][44], in models with scalar mediators bound-state effects appear to be either less severe, or relevant to a limited parameter space. In such models, the radiative capture into bound states suffers from two cancellations: (i) The lowest order s-wave contribution vanishes due to the orthogonality of the incoming and outgoing wavefunctions, thus abdicating the leading order to the p-wave.…”

Radiative bound-state formation in unbroken perturbative non-Abelian theories and implications for dark matter

“…In the case of asymmetric DM [13], the formation of stable bound states may produce novel direct [14,15] and indirect detection signals [16][17][18][19], as well as affect the DM selfscattering inside haloes [20]. In confining theories, bound states may set the DM mass scale [21,22], and relate it to that of ordinary matter [23]. Finally, DM bound states may have implications for collider experiments [3,[24][25][26].…”

Oscillating composite asymmetric dark matter

“…Composite ADM models based on QCD-like strong dynamics [7,8,[15][16][17][18][19][20][21][22][23][24] are particularly motivated by two reasons. First, strong dynamics naturally provides a large annihilation cross-section, which is an important feature for successful ADM so that the symmetric components annihilate away and the asymmetric component becomes the dominant component of the DM abundance.…”