Production regimes for Self-Interacting Dark Matter

Abstract

In the context of Self-Interacting Dark Matter as a solution for the small-scale structure problems, we consider the possibility that Dark Matter could have been produced without being in thermal equilibrium with the Standard Model bath. We discuss one by one the following various dark matter production regimes of this kind: freeze-in, reannihilation and dark freeze-out. We exemplify how these mechanisms work in the context of the particularly simple Hidden Vector Dark Matter model. In contrast to scenarios where there is thermal equilibrium with the Standard Model bath, we find two regimes which can easily satisfy all the laboratory and cosmological constraints. These are dark freeze-out with 3-to-2 annihilations and freeze-in via a light mediator. In the first regime, different temperatures in the visible and the Dark Matter sectors allow us to avoid the constraints coming from cosmic structure formation as well as the use of non-perturbative couplings to reproduce the observed relic density. For the second regime, different couplings are responsible for Dark Matter relic density and self-interactions, permitting to surpass BBN, X-ray, CMB and direct detection constraints.

The waning of the WIMP? A review of models, searches, and constraints

“…The interactions between the latter and the DM are then embedded in the covariant derivative 31 After spontaneous symmetry 30 The DM as a gauge boson of the dark sector connected to the SM through the SM-Higgs sector has also been proposed, for different DM production mechanisms, in Refs. [310,311]. 31 We have adopted the same definition of the covariant derivative as of Ref.…”

Elastically Decoupling Dark Matter

“…Unfortunately, the dark matter predicted by this scheme is too light ( 100 eV) to be consistent with the observed large-scale structure [2,3]. Recently, an interesting variation has been proposed, dubbed the strongly interacting massive particle or SIMP [4,5] (for extensions and variations, see [6][7][8][9][10]). In this model, the relic abundance is still set by selfannihilation, but the elastic scattering process is strong enough to sustain the thermal equilibrium between the SM and DM sectors until freeze-out occurs.…”

Cosmic abundances of SIMP dark matter

“…On the other hand, in the case of SIMP dark matter that is based on the 3 → 2 annihilation, we need to do the thermal averages for two (relative) velocities of dark matter in the initial states. Given that the velocity dependence of the 3 → 2 annihilation depends on the properties of dark matter [2][3][4][5][6][7][8] and the existence of resonance poles [8], it is worthwhile to make a systematic study of the thermal averages for 3 → 2 and higher-order annihilation processes in general.…”

“…For instance, in the case of fermionic SIMP, the initial states in the 3 → 2 process can be all fermions as discussed in refs. [15,16] while the case of vector SIMP was discussed [6] or will be published elsewhere [7].…”