  Extensions of the Standard Model with an extra U'(1) abelian group
generically generate terms coming from loops of heavy fermions, leading to
three gauge boson couplings, in particular Z'Z gamma. We show that WMAP data
constrains the gauge coupling of the group g_D to values comparable with the
electro-weak ones, rather independently of the mass of Z'. Moreover, the model
predicts a monochromatic gamma-ray line which can fit a 130 GeV signal at the
FERMI telescope for natural values of the Chern-Simons terms and a dark matter
mass around 144.5 GeV.
