  The analytic structure of elementary correlation functions of a quantum field
is relevant for the calculation of masses of bound states and their time-like
properties in general. In quantum chromodynamics, the calculation of
correlation functions for purely space-like momenta has reached a high level of
sophistication, but the calculation at time-like momenta requires refined
methods. One of them is the contour deformation method. Here we describe how to
employ it for three-point functions. The basic mechanisms are discussed for a
scalar theory, but they are the same for more complicated theories and are thus
relevant, e.g., for the three-gluon or quark-gluon vertices of quantum
chromodynamics. Their inclusion in existing truncation schemes is a crucial
step for investigating the analytic structure of elementary correlation
functions of quantum chromodynamics and the calculation of its spectrum from
them.
