Factorisation of scattering on the string worldsheet

The quantisation of string theories on curved backgrounds is a notoriously difficult task. One approach that is proving very powerful when string non-linear sigma model is integrable is to bootstrap a factorised S matrix on the two-dimensional string worldsheet. The symmetry-based bootstrap approach must however be checked by perturbative computations. This thesis will perturbatively verify the factorisation of the three-particle into three-particle scattering processes into a sequence of two-into-two processes. Prerequisites for the thesis are a working knowledge of quantum field theory.