The answer to the scattering problem in a complete theory of quantum gravity remains a fundamental open question in modern theoretical physics. Historical approaches to this problem include both bottom-up methods (e.g. perturbative quantum field theory / effective field theory) as well as top-down constructions (e.g. string theory or more general model-building). Unfortunately, these investigations to date have failed, respectively, to provide sharp answers or to capture uniquely the observed features of the real world. Nevertheless, in recent years, meaningful progress has arisen from a hybrid approach in which symmetries are identified and exploited to constrain the gravitational S-matrix. In this talk, I will explain how these symmetry considerations motivate a new proposal for a holographic correspondence. Known as “celestial holography”, this correspondence is a proposed equivalence between gravitational scattering in asymptotically flat spacetimes and a conformal field theory living on the celestial sphere. Remarkably, the process of so-reformulating the physics has unearthed new structure underlying the gravitational scattering problem. Notably, gravitational scattering admits an infinite-dimensional symmetry, which has been now identified as the w(1+infinity) symmetry previously appearing in other two-dimensional physical systems. These symmetries imply an infinite number of constraints on scattering amplitudes, which physically enforce universal behavior in the infrared.
Host: Yuan Xin (yuan.xin@yale.edu)