Self-interacting asymmetric dark matter coupled to a light massive dark photon

Abstract

Dark matter (DM) with sizeable self-interactions mediated by a light species offers a compelling explanation of the observed galactic substructure; furthermore, the direct coupling between DM and a light particle contributes to the DM annihilation in the early universe. If the DM abundance is due to a dark particle-antiparticle asymmetry, the DM annihilation cross-section can be arbitrarily large, and the coupling of DM to the light species can be significant. We consider the case of asymmetric DM interacting via a light (but not necessarily massless) Abelian gauge vector boson, a dark photon. In the massless dark photon limit, gauge invariance mandates that DM be multicomponent, consisting of positive and negative dark ions of different species which partially bind in neutral dark atoms. We argue that a similar conclusion holds for light dark photons; in particular, we establish that the multi-component and atomic character of DM persists in much of the parameter space where the dark photon is sufficiently light to mediate sizeable DM self-interactions. We discuss the cosmological sequence of events in this scenario, including the dark asymmetry generation, the freeze-out of annihilations, the dark recombination and the phase transition which gives mass to the dark photon. We estimate the effect of self-interactions in DM haloes, taking into account this cosmological history. We place constraints based on the observed ellipticity of large haloes, and identify the regimes where DM self-scattering can affect the dynamics of smaller haloes, bringing theory in better agreement with observations. Moreover, we estimate the cosmological abundance of dark photons in various regimes, and derive pertinent bounds.1 Since the primary incentive for considering asymmetric DM is not any theoretical expectation of new physics related to the electroweak interactions of the SM, invoking dark interactions and dark light species is a completely natural possibility which does not remove any of the motivation for this class of theories. 2 If asymmetric DM carries non-Abelian gauge charges, gauge-charge neutrality can often be ensured also by an appropriate combination of the various "flavours" or "colours" of the DM multiplet(s). Referring again to ordinary matter, the valence quarks of protons and neutrons form SU(3)c-neutral combinations.

Scattering, damping, and acoustic oscillations: Simulating the structure of dark matter halos with relativistic force carriers

“…While it is not required, such a large cross section makes it reasonable to consider the existence of light force carriers in the dark sector. This could occur, for example, in dark atom models interacting through dark photons [34,48,[50][51][52][53][54][55][56][57], in mirror dark matter models [35][36][37][38][39][40][41][42]58,59,85], or dark matter coupled to Standard Model photons [60][61][62][63][64][65][66][67], neutrinos [24][25][26][27][28][29][30][31][32][33], or to some other new light particle [68][69][70][71][72][73][86][87][88].…”

“…While there are many SIDM scenarios that mediate the self-scattering interaction through a light force carrier, in this paper we will use the dark atom model as a benchmark [34][35][36][37][38][39][40][41][42]48,[50][51][52][53][54][55][56][57][58][59]. In this model, dark matter is composed of two different particles, oppositely charged under a new long-range Abelian gauge group Uð1Þ D , mediated by a dark photon ϕ.…”

Dissipative dark matter explains rotation curves

“…[22,23,24,25,26,27,28,29,30] (see also [31] for a more detailed bibliography). Such models allow for a very rich dark matter phenomenology, especially if the hidden sector contains unbroken gauge interactions.…”

Asymmetric dark matter stars

“…DM self-interactions have already been proposed and studied in different contexts [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35]. DM numerical simulations including self-interactions favor a DM-DM cross section per DM mass between 0.1 − 10 cm 2 /g.…”