Description
In this short introductory lecture, we will review the rudiments of the calculation
of tree-level string scattering amplitudes by means of the generating functional method.
This entails first translating external states’ vertex operators into suitable differential
operators acting on exponential factors. Calculating then a given tree-level amplitude
amounts to acting on a “generalised” Koba-Nielsen factor with its external states’
differential operators and computing the resulting worldsheet integral.