Non-perturbative flow equations from continuous unitary transformations

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dc.contributor.advisorScholtz, Frederik G.en_ZA
dc.contributor.advisorGeyer, H. B.en_ZA
dc.contributor.authorKriel, Johannes Nicolaasen_ZA
dc.contributor.otherUniversity of Stellenbosch. Faculty of Science. Dept. of Physics.en_ZA
dc.date.accessioned2008-07-16T09:21:11Zen_ZA
dc.date.accessioned2010-06-01T09:06:57Z
dc.date.available2008-07-16T09:21:11Zen_ZA
dc.date.available2010-06-01T09:06:57Z
dc.date.issued2005-12
dc.descriptionThesis (MSc (Physics))--University of Stellenbosch, 2005.
dc.description.abstractThe goal of this thesis is the development and implementation of a non-perturbative solution method for Wegner’s flow equations. We show that a parameterization of the flowing Hamiltonian in terms of a scalar function allows the flow equation to be rewritten as a nonlinear partial differential equation. The implementation is non-perturbative in that the derivation of the PDE is based on an expansion controlled by the size of the system rather than the coupling constant. We apply this method to the Lipkin model and obtain very accurate results for the spectrum, expectation values and eigenstates for all values of the coupling and in the thermodynamic limit. New aspects of the phase structure, made apparent by this non-perturbative treatment, are also investigated. The Dicke model is treated using a two-step diagonalization procedure which illustrates how an effective Hamiltonian may be constructed and subsequently solved within this framework.en
dc.identifier.urihttp://hdl.handle.net/10019.1/3125
dc.language.isoen
dc.publisherStellenbosch : University of Stellenbosch
dc.rights.holderUniversity of Stellenbosch
dc.subjectDissertations -- Physicsen
dc.subjectTheses -- Physicsen
dc.subjectUnitary transformationsen
dc.subjectFlow equationsen
dc.titleNon-perturbative flow equations from continuous unitary transformationsen
dc.typeThesis
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