Chapter 10: The Development of MPI Modeling in Pythia

Many of the basic ideas in multiparton interaction (MPI) phenomenology were first developed in the context of the Pythia event generator, and MPIs have been central in its modeling of both minimum-bias (MB) and underlying-event physics in one unified framework. This chapter traces the evolution towards an increasingly sophisticated description of MPIs in Pythia, including topics such as the ordering of MPIs, the regularization of the divergent QCD cross-section, the impact-parameter picture, color reconnection, multiparton PDFs and beam remnants, interleaved and intertwined evolution, and diffraction.