On the Majorana Representation for Spin 1/2

This thesis studies the Majorana representation for spin 1/2, which enables quantum-field-theoretical methods for spin observables. The representation is applied to the Bose-Kondo and the spin-boson model. We establish efficient methods for the computation of spin correlation functions and reconsider the RG behavior of the subohmic anisotropic Bose-Kondo model. We review the experimental relevance of four-point spin correlation functions and analyze the noise of susceptibility