Theoretical Physics Seminar: Lionel Mason

Title: The twistor origin of hidden w-infinity symmetries in celestial gravity

Abstract: Recently in their celestial holography programme, Strominger 
and coworkers attempt to provide a holographic description of 
conventional 4d gravity.  In their investigations, they uncovered a 
hidden w-infinity symmetry in their `celestial soft OPEs' for graviton 
scattering.  This talk will explain the origin of this symmetry in terms 
of old ideas of Newman and Penrose based on light-cone cuts of null 
infinity and their description in terms of asymptotic twistors and 
certain sigma models in asymptotic twistor space.  W_n symmetries were 
introduced by Zamolodchikov as higher spin symmetries in 2d conformal 
field theories.  These were given a geometric interpretation for 
n=infinity as area-preserving diffeomorphisms of the plane.  I will 
explain how the corresponding loop algebra becomes a hidden symmetry of 
self-dual gravity via Penrose's nonlinear graviton construction.  The 
action of this symmetry on the tree-level S-matrix of full gravity 
beyond the self-dual sector will then be obtained from its action on a 
sigma model in the asymtotic twistor space of a general space-time.  
This talk is based on 2110.06066 and 2103.16984.