Dark photons in the Dalitz-like decay of a scalar
  The couplings of the Standard Model sector to the scale invariant degrees of freedom can open the possibility to study dark photons (DP). The Dalitz-like decay of the (Higgs-like) scalar boson into a single photon and DP is studied. The interaction between DP and quarks is mediated by the derivative of the scalar field - the dilaton, the virtual (fictitious) state. The mass of the dilaton does not enter the final solutions. Upper limits are set on the DP mass, the mixing strength between the standard photon and DP. The model does allow to estimate the DP mass with the value of 4.5 MeV. 
G.A. Kozlov
hep-ph hep-th