Light scalars coupled to photons and non-newtonian forces
  A particle $\phi$ coupling to two photons couples also to charged particles, like protons, through a loop. If the particle is a light scalar this induced coupling to protons leads to non-newtonian forces. We show that the experimental constraints on exotic, fifth-type forces lead to stringent constraints on the $\phi\gamma\gamma$ coupling. 
Arnaud Dupays, Eduard Masso', Javier Redondo and Carlo Rizzo