“Causality constraints on corrections to Einstein gravity"

In this talk I will describe constraints from causality and unitarity on 2→2 graviton scattering in four-dimensional weakly-coupled effective field theories. Together, causality and unitarity imply dispersion relations that connect low-energy observables to high-energy data. Using such dispersion relations, I will explain how to derive two-sided bounds on gravitational Wilson coefficients in terms of the mass M of new higher-spin states. Such bounds have many implications. For instance, they show that gravitational interactions must shut off uniformly in the limit G→0, prove the scaling with M expected from dimensional analysis, and impose a species bound on theories with a large number of matter fields. In addition they demonstrate the gravity must be weakly coupled at all scales below Planck. Time permitting, I will also comment on the experimental implications of the bounds.