Gravity seminar - Shuang-Yong Zhou Seminar

Locality, unitary and analyticity are some of the most fundamental properties of (local) quantum field theory. I will show how requiring a local, analytic, unitary UV completion for a low energy effective theory (EFT) can impose positivity bounds on the operator coefficients in the EFT. These positivity bounds take the form of constraints on combinations of the pole subtracted scattering amplitude and its derivatives. I will first demonstrate the main idea with the simple case of a massive scalar field, and then discuss the technical subtleties that arise when generalising to cases with nonzero spins. Finally, I will apply these positivity bounds to a couple of example EFTs which are popular in cosmology, including massive galileon and massive gravity.