String Theory seminar - Lionel Mason Seminar

Abstract: This talk has two parts. The first explains how the gravitational phase space for 4d gravity can be re-expressed, using old ideas of Newman and Penrose on null infinity and asymptotic twistor spaces, so as to geometrically realize Strominger and coworkers celestial Lw-infinity symmetry. It will be explained how this geometrical realization becomes particularly sharp in split signature. The second part introduces an open chiral sigma model with target the asymptotic twistor space. The full gravity tree-level S-matrix can then be obtained from tree correlators of this model. The action of the Lw_{1+\infty} symmetry on the tree-level S-matrix of full gravity beyond the self-dual sector is then realized by the action of certain vertex operators and acts on the full amplitude. This was unclear in the original derivation from soft limits in the self-dual sector.