Short Distance Repulsive Gravity as a Consequence of Non Trivial PPN Parameters $\beta$ and $\gamma$

Abstract

We look for a graviton-dilaton theory which can predict non trivial values of the PPN parameters $\beta$ and/or $\gamma$ for a charge neutral point star, without any naked singularity. With the potential for dilaton $\phi$ set to zero, it contains one arbitrary function $\psi(\phi)$. Our requirements impose certain constraints on $\psi$, 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 Schwarzschild radius $r_0$. There is also no horizon for $r > r_0$. These results suggest that black holes are unlikely to form in a stellar collapse in this theory.