Axionlike particle assisted strongly interacting massive particle

We propose a new realization of strongly interacting massive particles (SIMPs) as self-interacting dark matter, where SIMPs couple to the standard model (SM) sector through an axionlike particle. Our model overcomes major obstacles accompanying the original SIMP model, such as a missing mechanism of kinetically equilibrating SIMPs with the SM plasma as well as marginal perturbativity of the chiral Lagrangian density. Remarkably, the parameter region realizing ${\sigma }_{\mathrm{self}}/m_{\mathrm{DM}}\simeq 0.1–1{\mathrm{cm}}^2/\mathrm{g}$ is within the reach of future beam dump experiments such as the Search for Hidden Particles experiment.

Figure 1

Shown are $m_{\pi }–{\alpha }_{\pi }$ planes of the hidden sector. We assume that $N_c=3$, $N_f=4$, and $C_{\varphi \gamma \gamma }=3$. ${\theta }_H$ is taken to be 0 (left panel) and 2 (right panel). Black lines give the observed DM abundance (${\mathrm{\Omega }}_{\mathrm{DM}}{h}^2=0.12$) for $f=100$ and 300 GeV from the left to the right in each panel. In the red hatched band, the pion self-scattering achieves the SIDM cross section, i.e., $0.1{\mathrm{cm}}^2/\mathrm{g}\le {\sigma }_{\mathrm{self}}/m_{\pi }\le 1{\mathrm{cm}}^2/\mathrm{g}$. In the magenta shaded region, the $3\to 2$ process dominates the semiannihilation and thus determines the pion freeze-out. In the green region, the pion mass exceeds a naïve cutoff scale of the chiral Lagrangian density [see Eq. (3)] [34, 35]: $m_{\pi }\ge 2\pi f_{\pi }/\sqrt{N_c}$. Constraints on the ALP from NuCal (orange), CHARM (dark cyan), SLAC E-137 & E-141 (gray), and SN1987A (light cyan at the bottom right corner) are also shown. We convert the constraints to those on the $m_{\pi }–{\alpha }_{\pi }$ plane by imposing $m_{\varphi }=m_{\pi }$ so as not to heat up the DM pions through the semiannihilation in the course of the chemical freeze-out and by regarding $f$ as a function of $m_{\pi }$ and $f_{\pi }$ determined by the observed DM abundance. The orange dotted line is the projected sensitivity of the Belle II experiment for an ALP search [45]. The projected SHiP experiment will examine the region below the blue dashed lines, which covers a large part of the parameter space where the observed DM abundance and the SIDM cross section are simultaneously achieved.