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Strongly interacting singlet scalar dark matter during reheating

Geneviève Bélanger, Nicolás Bernal, Alexander Pukhov

Abstract

We revisit the singlet scalar dark matter model in the presence of a non-standard cosmological history prior to radiation domination. We focus on the regime in which the relic abundance is set by 4-to-2 self-annihilations while the dark and visible sectors remain in kinetic equilibrium, i.e. the standard strongly interacting massive particle (SIMP) framework. In the conventional radiation-dominated cosmology, this realization is not viable, as it requires sub-MeV masses and large quartic couplings in tension with bounds on dark matter self-interactions. We show that this conclusion is significantly modified if freeze-out occurs during non-standard cosmological eras. The altered Hubble expansion rate and the possible non-conservation of the standard model entropy change the freeze-out dynamics, allowing the observed relic density to be achieved with perturbative couplings and consistent with astrophysical constraints. We determine the region where SIMP production dominates over the WIMP mechanism and confront the viable parameter space with current and future direct detection and collider bounds.

Strongly interacting singlet scalar dark matter during reheating

Abstract

We revisit the singlet scalar dark matter model in the presence of a non-standard cosmological history prior to radiation domination. We focus on the regime in which the relic abundance is set by 4-to-2 self-annihilations while the dark and visible sectors remain in kinetic equilibrium, i.e. the standard strongly interacting massive particle (SIMP) framework. In the conventional radiation-dominated cosmology, this realization is not viable, as it requires sub-MeV masses and large quartic couplings in tension with bounds on dark matter self-interactions. We show that this conclusion is significantly modified if freeze-out occurs during non-standard cosmological eras. The altered Hubble expansion rate and the possible non-conservation of the standard model entropy change the freeze-out dynamics, allowing the observed relic density to be achieved with perturbative couplings and consistent with astrophysical constraints. We determine the region where SIMP production dominates over the WIMP mechanism and confront the viable parameter space with current and future direct detection and collider bounds.
Paper Structure (7 sections, 29 equations, 4 figures)

This paper contains 7 sections, 29 equations, 4 figures.

Table of Contents

  1. Introduction
  2. The Set-up
  3. Beyond standard cosmology
  4. Singlet scalar DM
  5. Strongly interacting singlet scalar DM during reheating
  6. Conclusions
  7. Interaction rates

Figures (4)

  • Figure 1: Leading processes for the 4-to-2 DM annihilation, in the limit of small $\lambda_{\Phi S}$.
  • Figure 2: Contours for the freeze out temperature $x_\text{fo} \equiv m/T_\text{fo}$ in the plane [$m, \lambda_S$], for $x_\text{fo} = 2$, 5, 10, and 15. The black lines correspond to the standard cosmological scenario, while the blue lines correspond to an early matter domination ($w = 0$ with $\alpha = 3/8$) with $T_\text{rh} = 1$ GeV.
  • Figure 3: Parameter space that fits the entire DM relic abundance through the SIMP mechanism, for $T_\text{rh} = 10^{-2}$ GeV, $10^2$ GeV, $10^6$ GeV and $10^{10}$ GeV, assuming an early matter dominated era ($w=0$ and $\alpha = 3/8$). The blue lines correspond to the standard cosmological scenario. Left panel: The red area are in tension with the Bullet cluster, perturbativity, BBN, or require a relativistic freeze-out. Right panel: The green area are in tension with direct DM searches and the invisible decay of the Higgs while in the red area DM does not reach kinetic equilibrium with the SM, gives rise to a WIMP solution or is ruled out by BBN.
  • Figure 4: Same as Fig. \ref{['fig:m-ls']} but for a radiation-dominated scenario ($w=1/3$) with $\alpha = 1/4$ (top) or $\alpha = 3/4$ (bottom).