HET Seminar - Graviton Loops and Negativity

Causality and unitary lead to sharp constraints on weakly-coupled gravitational effective field theories. They imply dispersion relations that can be used to derive sharp bounds on higher derivative couplings. We study the modifications of these statements from including 1-loop effects in the EFT. We show that crossing-symmetric dispersion relation is a natural tool for computing the 1-loop corrections to dispersive bounds. We use this method to study the positivity bounds derived at tree-level, and find that generically they can be violated due to graviton loops in the EFT. Additionally, we revisit the problem of the logarithmically divergent 4D dispersive bounds. We show that one can resum the divergences at all loop orders and obtain an interesting finite 4D bound using the eikonal formula describing the universal behavior of gravitational amplitudes near the forward limit. Based on work to appear with Julio Parra-Martinez.