Scalar and fermion two-component SIMP dark matter with an accidental ℤ4 symmetry

Abstract

In this paper, we construct for the first time a two-component strongly interacting massive particles (SIMP) dark matter (DM) model, where a complex scalar and a vector-like fermion play the role of the SIMP DM candidates. These two particles are stable due to an accidental ℤ4 symmetry after the breaking of a U(1)D gauge symmetry. By introducing one extra complex scalar as a mediator between the SIMP particles, this model can have 3 → 2 processes that determine the DM relic density. On the other hand, the SIMP DM particles can maintain kinetic equilibrium with the thermal bath until the DM freeze-out temperature via the U(1)D gauge couplings. Most importantly, we find an unavoidable two-loop induced 2 → 2 process tightly connecting to the 3 → 2 process that would redistribute the SIMP DM number densities after the chemical freeze-out of DM. Moreover, this redistribution would significantly modify the predictions of the self-interacting cross section of DM compared with other SIMP models. It is crucial to include the two-loop induced 2 → 2 annihilations to obtain the correct DM phenomenology.

Exponential Enhancement of Dark Matter Freezeout Abundance

“…1 initially but "bounces" to a different (exponentially rising) equilibrium distribution while in thermal equilibrium. Such nontrivial behavior of the number density of a species in thermal equilibrium had previously also been observed in earlier works [16][17][18][19], although the associated mechanism was not discussed in detail. This note is only a short summary of the main ideas presented in [15]; the interested reader is referred to that paper for further details.…”

Bouncing Dark Matter

“…This feature has been observed in[23] for metastable dark sector particles (see also[24]), then in[25,26] for dark matter, but without detailed discussion of the mechanism.…”

An asymmetric SIMP dark matter model

“…For the case where the SIMP DM particles have zero chemical potentials, µ X, X,Z, Z = 0, see refs. [13,14] With this finding, the aim of this paper is concrete and straightforward. We want to build a UV complete model to realize the aSIMP scenario and to see its phenomenology.…”

“…To achieve the aSIMP scenario, we consider the two-component SIMP DM model (hereafter we dub it aSIMP model) studied in ref. [13], where the SM model is extended with a vectorlike fermion, N , and three complex singlet scalars, X, S, and φ. These exotic particles possess dark charges under a gauged U(1) D symmetry, and all SM particles are dark neutral under this new symmetry.…”

“…Since the particle contents and the Lagrangian density in the aSIMP model are exactly as same as the ones in ref. [13], for our purpose, here we only write down the relevant interactions and the mass spectra of the new particles in this model.…”