HEP Theory Journal Club

Dispersion relation(s) for conformal theories

Simon Caron-Huot

McGill

Dispersion relations, often called Kramers-Kronig relations, exploit causality to reconstruct the real part of a scattering amplitude from its imaginary (or absorptive) part, which is often easier to measure and or to compute. I will describe various forms of dispersion relations obtained recently for four-point CFT correlators: in coordinate space, Mellin space, or using novel Regge-Polyakov blocks, and their anticipated applications. These approaches all provide non-perturbative constraints on CFT spectra and in fact appear to be equivalent. As a first application, I will comment on a recent theorem (by Penedones, Silva& Zhiboedov) ruling out the existence of a consistent theory of gravity in AdS coupled to a single light scalar (and no other light field).