arXiv subjects

D. Gwion Evans

Publications and source records attributed to D. Gwion Evans.

5 recordsLinked to original sources

arXiv2026

Semi-Cosimplicial Hilbert Spaces with Isometric Coface Operators

Semi-cosimplicial objects in the category of Hilbert spaces with isometries which are motivated by non-commutative probability theory, in particular by the distributional symmetry of spreadability, are introduced and systematically developed in various directions: partial shifts, cohomology, Hessenberg form, a related graph, decomposition into labeled subspaces, representation theory of the infinite symmetric and braid groups, classification and extensions for semi-cosimplicial sets with injective coface maps and a toy version of spreadability.

math.OA↗

arXiv2018

When is the Cuntz-Krieger algebra of a higher-rank graph approximately finite-dimensional?

We investigate the question: when is a higher-rank graph C*-algebra approximately finite dimensional? We prove that the absence of an appropriate higher-rank analogue of a cycle is necessary. We show that it is not in general sufficient, but that it is sufficient for higher-rank graphs with finitely many vertices. We give a detailed description of the structure of the C*-algebra of a row-finite locally convex higher-rank graph with finitely many vertices. Our results are also sufficient to establish that if the C*-algebra of a higher-rank graph is AF, then its every ideal must be gauge-invariant. We prove that for a higher-rank graph C*-algebra to be AF it is necessary and sufficient for all the corners determined by vertex projections to be AF. We close with a number of examples which illustrate why our question is so much more difficult for higher-rank graphs than for ordinary graphs.

math.OA↗

arXiv2016

Semi-Cosimplicial Objects and Spreadability

To a semi-cosimplicial object (SCO) in a category we associate a system of partial shifts on the inductive limit. We show how to produce an SCO from an action of the infinite braid monoid $\mathbb{B}^+_\infty$ and provide examples. In categories of (noncommutative) probability spaces SCOs correspond to spreadable sequences of random variables, hence SCOs can be considered as the algebraic structure underlying spreadability.

math.OA↗

arXiv2013

Non-abelian Weyl Commutation Relations and the Series Product of Quantum Stochastic Evolutions

We show that the series product, which serves as an algebraic rule for connecting state-based input/output systems, is intimately related to the Heisenberg group and the canonical commutation relations. The series product for quantum stochastic models then corresponds to a non-abelian generalization of the Weyl commutation relation. We show that the series product gives the general rule for combining the generators of quantum stochastic evolutions using a Lie-Trotter product formula.

math-ph↗

arXiv2007

On the K-theory of higher rank graph C*-algebras

Given a row-finite $k$-graph $Λ$ with no sources we investigate the $K$-theory of the higher rank graph $C^*$-algebra, $C^*(Λ)$. When $k=2$ we are able to give explicit formulae to calculate the $K$-groups of $C^*(Λ)$. The $K$-groups of $C^*(Λ)$ for $k>2$ can be calculated under certain circumstances and we consider the case $k=3$. We prove that for arbitrary $k$, the torsion-free rank of $K_0(C^*(Λ))$ and $K_1(C^*Λ))$ are equal when $C^*(Λ)$ is unital, and for $k=2$ we determine the position of the class of the unit of $C^*(Λ)$ in $K_0(C^*(Λ))$.

math.OA↗