Phenomenological Studies on String Fragmentation and Shower Expansions

The event generator PYTHIA is used for simulations of complex theoretical models for comparison to collider experiments like the Large Hadron Collider. This thesis focuses Quantum Chromodynamics phenomenology in PYTHIA — specifically parton showers and Lund string hadronization. For parton showers, a key way to test a shower’s accuracy is using tree-level expansions, which here we present a method to perform these shower expansions directly using event generation. We also present several extensions to the Lund string model, including the improvement of “junction” string modelling, additional models aimed to describe the behaviour of a collective of strings, and varying tension strings.