Nonlinear responses and three-particle correlators in correlated electron systems exemplified by the Anderson impurity model

Three-particle correlators are relevant for, among others, Raman, Hall, and nonlinear responses. They are also required for the next order of approximations extending dynamical mean-field theory diagrammatically. We present a general formalism on how to treat these three-particle correlators and susceptibilities, and we calculate the local three-particle response of the Anderson impurity model numerically. We find that genuine three-particle vertex corrections are sizable. In particular, it is not sufficient to just take the bare bubble terms or corrections based on the two-particle vertex. The full three-particle vertex must be considered.