Gamma-ray line from Nambu-Goldstone dark matter in a scale invariant extension of the Standard Model

A recently proposed scale invariant extension of the standard model is modified such that it includes a Dark Matter candidate which can annihilate into gamma-rays. For that a non-zero U(1)(Y) hypercharge Q is assigned to the fermions in a QCD-like hidden sector. The Nambu-Goldstone bosons, that arise due to dynamical chiral symmetry breaking in the hidden sector, are cold Dark Matter candidates, and the extension allows them to annihilate into two photons, producing a gamma-ray line spectrum. We find that the gamma-ray line energy must be between 0.7 TeV and 0.9 TeV with the velocity-averaged annihilation cross section 10(-30) similar to 10(-26) cm(3)/s for Q = 1/3. With a non-zero hypercharge Q, the hidden sector is no longer completely dark and can be directly probed by collider experiments.