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 $10^{ -30}\sim 10^{ -26}$ 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.
Categories: hep-ph astro-ph.HE hep-ex