Title: [NTU-NCTS String Seminar] Gravitational positivity bounds: implications for the swampland program
Speaker: Dr. Junsei Tokuda (IBS)
Time: June. 9, 2023 (Fri.) 14:30-15:30
Venue: Rm. 815, Dept. of Physics, NTU

Abstract:
In this talk, we extend so-called positivity bounds on four-point scattering amplitudes to the gravitational context by assuming the Reggeization of graviton exchange in quantum gravity. We obtain a twice-subtracted sum rule which gives an explicit relation between the gravitational Regge amplitude and low-energy observables. We also show that unitarity and crossing symmetry constrain the gravitational Regge amplitude, by using the finite energy sum rules (FESRs). Our results provide a manifestly infrared finite positivity bound on gravitational effective field theories (EFTs) in four spacetime dimensions. We also discuss a potential implication of positivity bounds on gravitational EFTs which turn out to be very interesting. In particular, under additional assumptions on the details of the Regge behavior, we find strong bounds on the simplest dark photon models which can be compared with experimental bounds, while the Standard Model easily satisfies the bounds. These results give phenomenological motivations for further studies of the Regge behavior.