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

摘要

We look for a graviton-dilaton theory which can predict non trivial values ofthe PPN parameters $\beta$ and/or $\gamma$ for a charge neutral point star,without any naked singularity. With the potential for dilaton $\phi$ set tozero, it contains one arbitrary function $\psi(\phi)$. Our requirements imposecertain constraints on $\psi$, which lead to the following generic and modelindependent novel results: For a charge neutral point star, the gravitationalforce becomes repulsive at distances of the order of, but greater than, theSchwarzschild radius $r_0$. There is also no horizon for $r > r_0$. Theseresults suggest that black holes are unlikely to form in a stellar collapse inthis theory.