String Theory seminar - Stephan Stieberger Seminar

Abstract: The celestial sphere is the target space for the proposal of flat space holography in which four-dimensional physics is encoded in two-dimensional celestial conformal field theory (CCFT). After giving some motivations we introduce the concepts and tools of physics on the celestial sphere. We shall discuss the symmetries and properties of celestial amplitudes. By introducing the concept of soft theorems on the celestial sphere and their corresponding Ward identities we shall give an explicit field realization of the operators generating superrotations and supertranslations. Equipped with these results we construct the full extended BMS and extended super BMS algebras of CCFT. Finally, we shall present a conformal block expansion of a celestial four-gluon amplitude in terms of primary fields. Interestingly, higher spin states show up in this expansion.