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Title: Exploring higher dimensional quantum field theories through fixed points
Author: Simms, R.
ISNI:       0000 0004 7659 0473
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2018
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Renormalization was popularised in the 1940s following the appearance of non- sensical infinities in the calculation of the self-energy of the electron. Notably this led to Quantum Electrodynamics becoming a fully renormalizable quantum field theory. One useful tool that emerges from the technical aspects of renormal- ization is the Renormalization Group. In particular, the β-function defines the variation of the coupling constants with energy. The vanishing of the β-function at a particular value of the coupling is known as a fixed point, the location of which can be found using perturbation theory. Properties of quantum field the- ories such as ultraviolet behaviour can be studied using these fixed points. The calculation of two different types of fixed points forms the spine of this thesis. In Part I the d-dimensional Wilson-Fisher fixed point is used to connect scalar quantum field theories in different space-time dimensions. Specifically we look at dimensions greater than four and explore the property of universality through the Vasil'ev large N expansion. Different universality classes are examined, the first contains φ4 theory with O(N) symmetry while another incorporates O(N)×O(m) Landau-Ginzburg-Wilson theory. In the latter we perform a full fixed point sta- bility analysis and conformal window search which determines where conformal symmetry is present. Part I develops techniques that may later be applicable to calculations involving beyond the Standard Model physics including asymptotic safety, quantum gravity and emergent symmetries. Part II focuses on the non-trivial Banks-Zaks fixed point of four dimensional Quantum Chromodynamics. Using a variety of colour groups and representations we calculate the location of the fixed point and corresponding critical exponents to pinpoint exactly where the true value of the conformal window lies. Additionally a number of different renormalization schemes are used, including the momentum subtraction (MOM) and interpolating momentum subtraction (iMOM) schemes. This allows us to study where in the conformal window scheme dependence is most apparent. Both the Landau gauge and maximal abelian gauge are utilized to extend the analysis. Throughout this thesis we compare and contrast perturbative results with non-perturbative calculations such as those performed in lattice.
Supervisor: Gracey, John Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral