3,151 research outputs found
The planar algebra of a semisimple and cosemisimple Hopf algebra
To a semisimple and cosemisimple Hopf algebra over an algebraically closed
field, we associate a planar algebra defined by generators and relations and
show that it is a connected, irreducible, spherical, non-degenerate planar
algebra with non-zero modulus and of depth two. This association is shown to
yield a bijection between (the isomorphism classes, on both sides, of) such
objects.Comment: 16 pages, 20 figures; content adde
Tangle-tree duality in abstract separation systems
We prove a general width duality theorem for combinatorial structures with
well-defined notions of cohesion and separation. These might be graphs and
matroids, but can be much more general or quite different. The theorem asserts
a duality between the existence of high cohesiveness somewhere local and a
global overall tree structure.
We describe cohesive substructures in a unified way in the format of tangles:
as orientations of low-order separations satisfying certain consistency axioms.
These axioms can be expressed without reference to the underlying structure,
such as a graph or matroid, but just in terms of the poset of the separations
themselves. This makes it possible to identify tangles, and apply our
tangle-tree duality theorem, in very diverse settings.
Our result implies all the classical duality theorems for width parameters in
graph minor theory, such as path-width, tree-width, branch-width or rank-width.
It yields new, tangle-type, duality theorems for tree-width and path-width. It
implies the existence of width parameters dual to cohesive substructures such
as -blocks, edge-tangles, or given subsets of tangles, for which no width
duality theorems were previously known.
Abstract separation systems can be found also in structures quite unlike
graphs and matroids. For example, our theorem can be applied to image analysis
by capturing the regions of an image as tangles of separations defined as
natural partitions of its set of pixels. It can be applied in big data contexts
by capturing clusters as tangles. It can be applied in the social sciences,
e.g. by capturing as tangles the few typical mindsets of individuals found by a
survey. It could also be applied in pure mathematics, e.g. to separations of
compact manifolds.Comment: We have expanded Section 2 on terminology for better readability,
adding explanatory text, examples, and figures. This paper replaces the first
half of our earlier paper arXiv:1406.379
A Lagrangian representation of tangles
We construct a functor from the category of oriented tangles in R^3 to the
category of Hermitian modules and Lagrangian relations over Z[t,t^{-1}]. This
functor extends the Burau representations of the braid groups and its
generalization to string links due to Le Dimet.Comment: 36 pages, 8 figure
The Kontsevich integral and quantized Lie superalgebras
Given a finite dimensional representation of a semisimple Lie algebra there
are two ways of constructing link invariants: 1) quantum group invariants using
the R-matrix, 2) the Kontsevich universal link invariant followed by the Lie
algebra based weight system. Le and Murakami showed that these two link
invariants are the same. These constructions can be generalized to some classes
of Lie superalgebras. In this paper we show that constructions 1) and 2) give
the same invariants for the Lie superalgebras of type A-G. We use this result
to investigate the Links-Gould invariant. We also give a positive answer to a
conjecture of Patureau-Mirand's concerning invariants arising from the Lie
superalgebra D(2,1;alpha).Comment: Published by Algebraic and Geometric Topology at
http://www.maths.warwick.ac.uk/agt/AGTVol5/agt-5-45.abs.htm
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