Communication with SIMP dark mesons via Z′-portal

We consider a consistent extension of the SIMP models with dark mesons by including a dark U(1)D gauge symmetry. Dark matter density is determined by a thermal freeze-out of the 3→2 self-annihilation process, thanks to the Wess–Zumino–Witten term. In the presence of a gauge kinetic mixing between the dark photon and the SM hypercharge gauge boson, dark mesons can undergo a sufficient scattering off the Standard Model particles and keep in kinetic equilibrium until freeze-out in this SIMP scenario. Taking the SU(Nf)×SU(Nf)/SU(Nf) flavor symmetry under the SU(Nc) confining group, we show how much complementary the SIMP constraints on the parameters of the dark photon are for current experimental searches for dark photon.