The inclusion of ghosts in Landau gauge Schwinger-Dyson studies of infrared QCD
It is widely believed that Quantum Chromodynamics (QCD) is the theory that describes the strong interaction. In the infrared region of the theory, the perturbative expansion breaks down and so, other techniques must be used. One such technique is the study of the Schwinger-Dyson equations. In this thesis is presented such a study. It is shown that the ghost sector of QCD may be crucial to the understanding of the infrared behaviour. Conventionally, the Slavnov- Taylor identity is used to truncate the Schwinger-Dyson equations but it is found that for the ghost-gluon vertex, such an identity cannot be used in an appropriate manner. In order to extract information, a new technique is presented, based on the powerlaw behaviour of the two-point functions in the infrared. By demanding consistency in the full equations in Landau gauge and multiplicative renormalisability, it is found that in general, the gluon propagator dressing function cannot diverge and the ghost propagator function cannot vanish in the infrared. Further, it is shown that the powerlaw behaviour depends on a certain kinematical limit of only one function connected with the ghost-gluon vertex.