Topological state sum models in four dimensions, half-twists and their applications

Bärenz, Manuel (2017) Topological state sum models in four dimensions, half-twists and their applications. PhD thesis, University of Nottingham.

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Various mathematical tools are developed with the aim of application in mathematical physics.

In the first part, a new state sum model for four-manifolds is introduced which generalises the Crane-Yetter model. It is parametrised by a pivotal functor from a spherical fusion category into a ribbon fusion category. The special case of the Crane-Yetter model for an arbitrary ribbon fusion category C arises when we consider the canonical inclusion C↪Z(C) into the Drinfeld centre as the pivotal functor. The model is defined in terms of handle decompositions of manifolds and thus enjoys a succinct and intuitive graphical calculus, through which concrete calculations become very easy. It gives a chain-mail procedure for the Crane-Yetter model even in the case of a nonmodular category.The nonmodular Crane-Yetter model is then shown to be nontrivial: It depends at least on the fundamental group of the manifold. Relations to the Walker-Wang model and recent calculations of ground state degeneracies are established.

The second part develops the theory of involutive monoidal categories and half-twists (which are related to braided and balanced structures) further. Several gaps in the literature are closed and some missing infrastructure is developed. The main novel contribution are ``half-ribbon'' categories, which combine duals - represented by rotations in the plane by π - with half-twists, which are represented by turns of ribbons by π around the vertical axis. Many examples are given, and a general construction of a half-ribbon category is presented, resulting in so-called half-twisted categories.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Barrett, John W.
Krasnov, K.
Keywords: Topological quantum field theory ; state sum models ; quantum gravity ; category theory
Subjects: Q Science > QA Mathematics > QA611 Topology
Q Science > QC Physics > QC170 Atomic physics. Constitution and properties of matter
Faculties/Schools: UK Campuses > Faculty of Science > School of Mathematical Sciences
Item ID: 41720
Depositing User: Bärenz, Manuel
Date Deposited: 12 Jul 2017 04:40
Last Modified: 13 Oct 2017 01:15

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