Gauge checks, consistency of approximation schemes and numerical evaluation of realistic scattering amplitudes.
Technische Universität, Darmstadt
[Ph.D. Thesis], (2003)
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|Item Type:||Ph.D. Thesis|
|Title:||Gauge checks, consistency of approximation schemes and numerical evaluation of realistic scattering amplitudes|
In this work we discuss both theoretical tools to verify gauge invariance in numerical calculations of cross sections and the consistency of approximation schemes used in realistic calculations. We determine a finite set of Ward Identities for 4 point scattering amplitudes that is sufficient to verify the correct implementation of Feynman rules of a spontaneously broken gauge theory in a model independent way. These identities have been implemented in the matrix element generator O'Mega and have been used to verify the implementation of the complete standard Model in Rξ gauge. As a theoretical tool, we derive a new identity for vertex functions with several momentum contractions. The problem of the consistency of approximation schemes in tree level calculations is discussed in the last part of this work. We determine the gauge invariance classes of spontaneously broken gauge theories, providing a new proof for the formalism of gauge and flavor flips. The schemes for finite width effects that have been implemented in O'Mega are reviewed. As a comparison with existing calcuations, we study the consistency of these schemes in the process e-e+→ e- νe u dbar. The violations of gauge invariance caused by the introduction of running coupling constants are analyzed.
|Place of Publication:||Darmstadt|
|Divisions:||05 Department of Physics|
|Date Deposited:||17 Oct 2008 09:21|
|Last Modified:||07 Dec 2012 11:49|
|Referees:||Manakos, Prof. Dr. Panagiotis and Grewe, Prof. Dr. Norbert|
|Advisors:||Manakos, Prof. Dr. Panagiotis|
|Refereed:||23 June 2003|