The γ parameter in Brans-Dicke-like (light-)Scalar-Tensor theory with a universal scalar/matter coupling

Abstract: The post-Newtonian parameter \gamma\ resulting from a universal scalar/matter coupling is investigated in Brans-Dicke-like Scalar-Tensor theories where the scalar potential is assumed to be negligible. Conversely to previous studies, we use a perfect fluid formalism in order to get the explicit scalar-field equation. It is shown that the metric can be put in its standard post-Newtonian form. However, it is pointed out that 1-\gamma\ could be either positive, null or negative for finite value of \omega_0, depending on the coupling function; while Scalar-Tensor theories without coupling always predict \gamma<1 for finite value of \omega_0.