Types of quantum field thories
The probability amplitude for a process of scattering of fundamental particles or fundamental strings off each other. The collection of scattering amplitudes forms the S-matrix. In perturbation theory this is computed by the Feynman diagram perturbation series.
See also at motivic multiple zeta values.
In super Yang-Mills theory (and there in particular in the planar limit of N=4 D=4 super Yang-Mills theory) scattering amplitudes enjoy special symmetry properties, some of which can be used to extract information about scattering amplitudes in non-supersymmetric theories:
Wieland Staessens, Bert Vercnocke, Lectures on Scattering Amplitudes in String Theory (arXiv:1011.0456)
For more see at string scattering amplitude.
Motivic structures in scattering amplitudes (see at motives in physics) are discussed for instance in
See also the references at period.