Memory Correlators and Ward Identities in the 'in-in' Formalism

Abstract: The symmetries of asymptotically flat spacetimes impose constraints on observables at infinity. The consequences of this have been extensively explored for S-matrix elements, where soft theorems are known to be equivalent to Ward identities for asymptotic symmetries. However, recently there has been interest in broader classes of asymptotic observables. Here, we consider soft graviton insertions in the 'in-in' formalism. We derive a Ward identity for supertranslations and compute two point functions for the soft charges for 'in-in' correlators. We find that the connected memory correlators are non-trivial in this set up and can be straightforwardly inferred from the average null energy (ANEC) correlators using observations from celestial Conformal Field Theory (cCFT).