Effective field theories for heavy and light fermions.

2003

In this thesis, various aspects of different effective field theory (EFT) approximations to the Standard Model of elementary particle physics have been elaborated. The EFT's treated range from non-relativistic approximations to quantum electrodynamics (QED) and quantum chromodynamics (QCD), which can be applied if the quanta under consideration moves at velocities small compared with the speed of light, to chiral perturbation theory as well as the effective theory which emerges in the limit of a large number of colour degrees of freedom in QCD. The latter two constitute expansions in the energy of the process under investigation, and are applicable if this energy is small compared to a typi…