Scalar-tensor theories of gravity with Phi -dependent masses

The authors study new physical phenomena and constraints in generalized scalar-tensor theories of gravity with Phi -dependent masses. They investigate a scenario (which can arise in string theories) with two types of Phi -dependent masses which could correspond to visible and dark matter sectors. The parameters of this theory are constrained from post-Newtonian bounds, primordial nucleosynthesis and the age of the universe. They present a perfect fluid formalism for the dark matter sector with variable masses and find an entropy increase effect during the matter era and, in principle, a measurable effect on the motion of the halo of spiral galaxies. For the case of string effective theories, the constancy of gauge couplings provides new bounds which are orders of magnitude stronger than the previous ones.