Composite Dark Matter with Forbidden Annihilation

A dark matter model based on QCD-like SU(Nc) gauge theory with electroweakly interacting dark quarks is discussed. Assuming the dark quark mass m is smaller than the dynamical scale Λd ~ 4π fd, the main component of the dark matter is the lightest G-parity odd dark pion associated with chiral symmetry breaking in the dark sector. We show that nonzero dark quark mass induces the universal mass contribution to both G-parity odd and even pions, and their masses tend to be degenerate. As a result, dark pion annihilation into heavier G-parity even dark pion also affects the dark matter relic abundance. Thus, our setup naturally accommodates forbidden dark matter scenario and realizes heavy dark matter whose mass is O(1-100)~ TeV, which is different from conventional electroweakly interacting dark matter such as minimal dark matter. We also discuss CP-violation from θ-term in the dark gauge sector and find that the predicted size of electron electric dipole moment can be as large as ~ 10⁻³²~e~ cm.