Phenomenological motivation for gravitational positivity bounds: A case study of dark sector physics

Abstract

Positivity bounds on scattering amplitudes provide a necessary condition for a low-energy effective field theory to have a consistent ultraviolet completion. Their extension to gravity theories has been studied in the past years aiming at application to the swampland program, showing that positivity bounds hold at least approximately even in the presence of gravity. A theoretical issue in this context is how much negativity is allowed for a given scattering process. We show that this issue is relevant to physics within the scope of ongoing experiments, especially in the context of dark sector physics. A detailed analysis of dark photon scenarios is provided as an illustrative example. Our results do not merely show the phenomenological importance of the theoretical study of gravitational positivity bounds but also open up an exciting possibility of exploring the nature of quantum gravity via an experimental search of the dark sector.