Peter Christian Bruns

Multi-scale Chiral Dynamics: Some New Developments in Effective Quantum Field Theories Peter Christian Bruns

The presence of resonances generally leads to complications in the formulation of consistent effective quantum field theories, mainly due to the appearance of additional mass scales, such as e.g. the masses of the resonances. In this work, we explore two different ways in which resonances can be incorporated in the framework of Chiral Perturbation Theory, which is the low energy effective field theory of Quantum Chromodynamics (QCD). In the first part, we develop new flexible renormalization prescriptions which allow to evaluate consistently the contribution of resonance fields to various hadronic observables. In the second part, resonances are incorporated dynamically by means of a non-perturbative method, namely the Bethe-Salpeter integral equation. The main purpose here is the construction of a model framework for the description of kaon photoproduction, a process where resonances are known to be of great importance.