Short-distance repulsive gravity as a consequence of the non-trivial PPN parameters β and γ

We look for a graviton-dilaton theory which can predict non-trivial values of the PPN parameters β and/or γ for a charge neutral point star, without any naked singularity. With the potential for the dilaton φ set to zero, it contains one arbitrary function ψ(φ). Our requirements impose certain constraints on ψ, which lead to the following generic and model-independent novel results: For a charge neutral point star, the gravitational force becomes repulsive at distances of the order of, but greater than, the Schwarzchild radius r0. There is also no horizon for r > r0. These results suggest that black holes are unlikely to form in a stellar collapse in this theory.