Constraining novel soft gluon and graviton theorems

Abstract:

Recently there has been a revived interest in the universal behaviour of gluon and
graviton scattering amplitudes when one particle momentum becomes soft. Next to the well
established leading soft poles due to Low and Weinberg there are universal soft operators
describing the soft factorization also at the sub- or even sub-sub-leading order in the soft
momentum expansion. 
The structure of the soft graviton theorems has been recently connected to a
potential hidden symmetry of the quantum gravity S-matrix known as BMS symmetry. In my talk I shall
demonstrate that the form of the novel soft theorems essentially follows from rather elementary arguments
based on gauge and Poincare invariance of the scattering amplitudes as well as self-consitency of the
theorems. Our arguments can constrain the possible form of the soft gluon and graviton theorems both at tree
and loop-level.