Alfio Bonnano: Quantum Gravity Constraints on Fifth Forces

We investigate how ultraviolet (UV) completion in quantum gravity constrains possible fifth forces. In scalar–tensor theories, the radial mode of a broken O(N) scalar sector mediates a Yukawa correction to Newtonian gravity, characterized by a strength \alpha_Y and a range \lambda_Y. Using functional renormalization-group methods, we show that only a finite basin of infrared scalar–tensor couplings gives rise to trajectories that remain regular and approach a nonperturbative UV scaling regime. This UV-complete region maps into a restricted domain in the (\alpha_Y,\lambda_Y) plane, while its complement is excluded by theoretical consistency alone. Remarkably, part of this UV-excluded region lies below current experimental exclusion bounds, implying that future fifth-force searches can directly test—and potentially falsify—this class of UV-complete scalar–tensor models. I will also discuss possible broader implications for induced gravity and regular black-hole cores.