Gravitons, BRSTBMS4 Symmetry and its Cocycles from Horizontality Conditions 
Laurent Baulieu, Laboratoire de Physique ThÃ©orique et Hautes Ã‰nergies (LPTH 
Event Type: Special Seminar 

Time: 1:00 PM  2:15 PM 

Location: 726 Broadway, 940, CCPP Seminar 

Abstract: The BRST structure of the extended BondiMetznerSachs symmetry group of asymptotically flat manifolds is studied using the recently introduced framework of Beltrami field parametrization of fourdimensional metrics. The latter has interesting properties. In particular, it allows to geometrically define as fundamental fields the two physical degrees of freedom of asymptotic perturbative gravitons of asymptotically flat spaces. They are identified as excitations of the Beltrami differential of the asymptotic celestial sphere, enabling quite suggestive formula for the memory effect. The graded BRST BMS4 nilpotent differential operator that classically define the BMS symmetry transformations is actually based on four horizontality conditions. A number of BRST BMS4 cocycles can then be found, connected by descent equations. This indicates the possibility of anomalies for threedimensional Lagrangian theories possibly built from the principle of BRSTBMS4 invariance in the null boundaries $cal I ^pm$ of asymptotically flat spaces. Remarkably, the BMS anomaly cocycle $delta^1_3$ has a simplest and natural expression. Its descendants, $delta^2_2$ that can be associated with the occurrence of a central charge in Hamiltonian formalism, $delta^3_1$ and $delta^4_0$ have much less suggestive expressions that encode some subtilities of the four dimensional nature of the BMS4 symmetry. 