The Production And Evolution Of Strongly Self-Interacting Massive Dark Matter Particles In The Bounce Universe

The dark matter component in the standard cosmological model(ΛCDM model)is cold dark matter.One of the strongest candidates for cold dark matter is the weakly interacting massive particles(WIMP).In the WIMP model,freezing begins to occur when the temperature of the universe drops to the mass of dark matter.The freezing process is dominated by the annihilation of two dark matter particles into two standard model particles(called as 2 → 2 process),and forms the current observed dark matter energy density.This model successfully explained a series of astronomical observations including the formation of the large-scale structure of the universek＜ 0.1h/Mpc).However,its prediction on the small-scale structurek＞ 0.1h/Mpc)is inconsistent with the results of numerical simulation and preliminary astronomical observation.This problem is called’’small-scale crisis ’’.In order to address / alleviate this crisis,many new ideas have been proposed including the strongly interacting massive particle(SIMP)model.In the SIMP model,in addition to the 2 → 2 process,the reaction of three dark matter particles annihilating into two dark matter particles is also added(called as the 3 → 2 process).This new process can partially alleviate the small-scale crisis,so the SIMP model has attracted great attention.However,the current research on the SIMP model is limited to the inflationary cosmology model,which unavoidably encounters the problem of the initial singularity of the big bang.In this paper,we study the evolution of the SIMP dark matter model in the bounce universe.In the bounce cosmology model,the universe avoids the Big Bang initial singularity problem through a bouncing process of contraction to expansion.In this contractionbounce-expansion cosmic evolution background,we carefully analyze the production and freezing process of the SIMP dark matter model in three cases(thermal average crosssection independent of temperature case,fermion case and boson case).We found that the SIMP dark matter model not only has the same strong freezing process(Freeze-out)as the WIMP model with changed abundance,but also has a weak freezing process(Freezein)with unchanged abundance.At the same time,its production mode also has two cases: reaching thermal equilibrium(Equilibrium)and not reaching thermal equilibrium(Non-equilibrium).According to the combination classification of these two conditions(equilibrium / Non-equilibrium + freeze-in / freeze-out),According to the combination classification of these two conditions(Equilibrium/Non-equilibrium+Freeze-in/Freezeout),we found that the SIMP dark matter model has four possible evolution pathways:1.’’Non-equilibrium + Freeze-in ’’pathway 2.’’Non-equilibrium + Freeze-out’’pathway;3.’’Equilibrium + Freeze-in’’pathway;4.’’Equilibrium + Freeze-out’’pathway(due to Equilibrium condition and Freeze in condition coincidentally,the boson case thus missing the 3rd pathway).Further,we select an example from each of these four pathways,and through numerical solutions,we prove that they can all produce dark matter abundances that are consistent with the currently observed dark matter abundance,indicating that these four pathways are all possible dark matter evolution pathways.Our research results have important significance for understanding the evolutionary pathways of new dark matter models in different early universe evolution backgrounds,and lay a theoretical foundation for using new dark matter direct/indirect detection as a probe of the early universe.