Properties of D-Mesons from QCD Sum Rules with an Improved Spectral Function

Abstract

The goal of this thesis is to calculate properties of D-Mesons with QCD-Sum-Rules in order to understand the nature of D-Mesons with positive parity. The result is that such D-Mesons most probably are Mesons with a four quark rather than a two quark structure. In this thesis a spectral function which contains two resonances is used to calculate the decay constants of the first and the second resonance in the spectral function. Moreover, a Breit-Wigner curve instead of a delta-function is used to approximate the peaks of the resonances in the spectral function. The decay constants of the resonaces corresponding to the second peak in the spectral functions have never been calculated before.Also very practical problems are attacked, see the paragraph about the misscalculation of D-Meson Sum-Rules. Another topic of this thesis was the establishment of basical knowledge about QCD-Sum-Rules, the Operator-Product-Expansion and Dispersion-Integrals. A discussion of these topics and many explicite calculations are included.