Speaker: Sandipan Kundu, Johns Hopkins University
Speaker Institution: Johns Hopkins University
Title: Causality and energy conditions in QFT
Abstract: Causality places nontrivial constraints on QFT in Lorentzian signature, for example fixing the signs of certain terms in the low energy Lagrangian. In conformal field theory, I will show how causality is encoded in crossing symmetry and reflection positivity of Euclidean correlators, and derive constraints on the interactions of low-lying operators. I will explain the connection between the causality constraints in the lightcone limit and the averaged null energy condition. In particular, causality implies that the averaged null energy must be positive in interacting quantum field theory in flat spacetime. Whereas, for CFTs with large central charge and a sparse spectrum, causality constraints in the Regge limit leads to a stronger energy condition which is a generalization of the averaged null energy condition. This causality condition leads to non-trivial constraints on CFT 3-point couplings. In particular, I will also show that these constraints are consistent with the expectation that CFTs in this class, irrespective of their microscopic details, admit universal gravity-like holographic dual description.