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10/11/2010, 14:00 — 15:00 — Room P3.10, Mathematics Building

Marco Mackaay, *Univ. Algarve*

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Khovanov and Lauda's diagrammatic calculus for ${\mathrm{sl}}_{n}$

In this talk I plan to fill in some details of what I sketched in my previous talk. In particular I want to explain how one can obtain Khovanov and Lauda\'s calculus from bimodule maps corresponding to MOY-movies. In the end I will sketch the extended sl2 calculus for divided powers. References: 1) A. Lauda A categorification of quantum sl2, arXiv:0803.3652. 2) M. Khovanov and A. Lauda, A diagrammatic approach to categorification of quantum groups I-III, arXiv:0803.4121, arXiv:0804.2080, arXiv:0807.3250. 3) M. Khovanov, A. Lauda, M. Mackaay, M. Stosic, Extended graphical calculus for categorified quantum sl2, arXiv:1006.2866. 4) M. Mackaay, M. Stosic, P. Vaz, A diagrammatic categorification of the q-Schur algebra, arXiv:1008.1348.

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10/11/2010, 11:30 — 12:30 — Room P3.10, Mathematics Building

Olivier Brahic, *Instituto Superior Técnico*

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On higher analogues of symplectic fibrations

One can obtain simple models for abstract field theories by looking at closed forms defined on the total space of a fibration. For instance, in the case of hamiltonian fibrations, this is how Weinstein recovered Sternberg's minimal coupling, yielding a geometrical context for classical Yang-Mills theories. More generally, one can introduce 2-plectic fibrations and interpret the equations for coupling in terms of higher analogues of connections.

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27/10/2010, 15:30 — 16:30 — Room P3.10, Mathematics Building

Gonçalo Rodrigues, *Instituto Superior Técnico*

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Categorifying Measure Theory

Measure theory is the study of measures and their siamese twins, integrals. Its central position in analysis is partly explained because it provides us with large families of Banach spaces. In this seminar I will try to explain the why, the what and the how of categorifying measure theory. It will consist mostly in laying the groundwork so as to be able to explain the construction of the category of \"categorified integrable functionsänd the integral functor. Time permitting, I will also give a categorified Radon- Nikodym theorem. In a second, future seminar, I will give categorified versions of other basic theorems of measure theory (e.g. Fubini and Fubini-Tonelli on the equality of iterated integrals) and explain some new phenomena peculiar to the categorified setting and with no counterpart in ordinary measure theory.

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27/10/2010, 14:00 — 15:00 — Room P3.10, Mathematics Building

Jeffrey Morton, *Instituto Superior Técnico*

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Groupoidification in Physics

The Baez-Dolan groupoidification program describes linear-algebraic structures as reflections of those found in a category whose objects are groupoids, and whose morphisms are spans of groupoids. An extension of this program represents those structures in a 2-category of 2-vector spaces. Since quantum physics relies heavily on the category of Hilbert spaces, it has been possible to describe certain toy physical systems in this setting. The talk will describe these in terms of groupoids and spans with intrinsic combinatorial and geometric interest, and discuss how the 2-categorical extension applies in these models, including exotic statistics, and applications to 3D quantum gravity.

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12/10/2010, 15:30 — 16:30 — Room P4.35, Mathematics Building

Marco Mackaay, *Univ. Algarve*

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Categorifications of Hecke algebras, $q$-Schur algebras and quantum groups

This is meant to be a (rather incomplete) survey talk of the rapidly developing field of categorification. I will only concentrate on two of the various now existing approaches: the one using (singular) Soergel bimodules, due to Soergel (1992) and Williamson (2008), and the one using diagrams due to Khovanov and Lauda (2008) and Elias and Khovanov (2009). My intention is to explain the relation between the two approaches, as was worked out by Stosic, Vaz and myself.

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12/10/2010, 14:00 — 15:00 — Room P4.35, Mathematics Building

Anne-Laure Thiel, *Instituto Superior Técnico*

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Categorification of singular braid monoids and of virtual braid groups

Rouquier categorified braid groups, in the sense that he associated to each braid a complex of Soergel bimodules such that complexes associated to isotopic braids are homotopy equivalent. I will start with recalling Rouquier's construction and then extend this result to singular braids and to virtual braids.

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12/10/2010, 12:15 — 13:15 — Room P4.35, Mathematics Building

Rui Carpentier, *Instituto Superior Técnico*

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3-colorings of cubic graphs and operators

We consider a monoidal category consisting of cubic graphs with free ends as morphisms between finite sets of points on a line (in the same sense as the category of tangles). We give a linear representation of this category that codifies the number of edge 3-colorings of cubic graphs. Some developments and conjectures will be presented.

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16/07/2010, 14:00 — 15:00 — Room P3.10, Mathematics Building

Aleksandar Mikovic, *Univ. Lusofona, Lisboa*

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Lie crossed modules and gauge-invariant actions for 2-BF theories

We generalize the BF theory action to the case of a general Lie crossed module $(H\to G)$, where $G$ and $H$ are non-abelian Lie groups. Our construction requires the existence of $G$-invariant non-degenerate bilinear forms on the Lie algebras of $G$ and $H$ and we show that there are many examples of such Lie crossed modules by using the construction of crossed modules provided by short-complexes of vector spaces. We construct two gauge-invariant actions for 2-flat and fake-flat 2-connections with auxiliary fields. The first action is of the same type as the BFCG action introduced by Girelli, Pfeiffer and Popescu for a special class of Lie crossed modules, where $H$ is abelian. The second action is an extended BFCG action which contains an additional auxiliary field. We also construct a two-parameter deformation of the extended BFCG action, which we believe to be relevant for the construction of non-trivial invariants of knotted surfaces embedded in the four-sphere. http://arxiv.org/abs/1006.0903

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16/07/2010, 11:30 — 12:30 — Room P3.10, Mathematics Building

Rafael Diaz, *Universidad Sergio Arboleda, Colombia*

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Categorification, Feynman Integrals, and Quantization - II

We review the general notion of categorification in order to study quantization -- in the sense of deformation quantization -- and Feynman integrals from the viewpoint of category theory. The fairly abstract setting that we propose leads to a rather down to earth approach to these often elusive notions.

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16/07/2010, 10:00 — 11:00 — Room P3.10, Mathematics Building

Yasuyoshi Yonezawa, *Univ. of the Algarve and IST*

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Quantum $({\mathrm{sl}}_{n},\wedge {V}_{n})$ link invariant and matrix factorizations.

M. Khovanov and L. Rozansky constructed a homology for a link diagram whose Euler characteristic is the quantum link invariant associated to the quantum group $\mathrm{Uq}({\mathrm{sl}}_{n})$ and its vector representation ${V}_{n}$ by using matrix factorizations. In my thesis, I study a generalization of the Khovanov-Rozansky homology for the quantum link invariant associated to $\mathrm{Uq}({\mathrm{sl}}_{n})$ and its fundamental representations $\wedge {V}_{n}$. In this talk, I will define a new link invariant derived from the generalization of Khovanov-Rozansky homology.

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15/07/2010, 16:15 — 17:15 — Room P3.10, Mathematics Building

Jeffrey Morton, *University of Western Ontario*

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2-Linearization, Discrete and Smooth

This talk will introduce the construction "2-linearization", an extension of the "groupoidification" program of Baez and Dolan which seeks to interpret constructions in linear algebra in terms of groupoids and spans of groupoids. The 2-linearization construction finds this as a special case of a 2-functor $\Lambda :\mathrm{Span}(\mathrm{Gpd})\to 2\mathrm{Vect}$, where $2\mathrm{Vect}$ is the 2-category of Kapranov-Voevodsky 2-vector spaces. This 2-functor is constructed in terms of pairs of ambi-adjoint functors associated to each groupoid homomorphism, the "push" and "pull" operations, closely related to restriction and induction maps in representation theory, Grothendieck's 6-operation framework for sheaves, among other examples. We will begin with the discrete case, and consider generalizations to smooth groupoids. Finally we will consider some applications.

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15/07/2010, 14:00 — 15:00 — Room P3.10, Mathematics Building

Rafael Diaz, *Universidad Sergio Arboleda, Colombia*

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Categorification, Feynman Integrals, and Quantization - I

We review the general notion of categorification in order to study quantization -- in the sense of deformation quantization -- and Feynman integrals from the viewpoint of category theory. The fairly abstract setting that we propose leads to a rather down to earth approach to these often elusive notions.

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07/12/2009, 11:30 — 12:30 — Room P3.10, Mathematics Building

Branislav Jurco, *Max Planck Institute for Mathematics, Bonn, Germany*

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Introduction to nonabelian bundle 2-gerbes

We introduce nonabelian bundle 2-gerbes related to Lie 2-crossed modules and discuss their properties. Such bundle 2-gerbes are defined in terms of bundle 1-gerbes, which play a role similar to that of transition functions in the theory of principal bundles.

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30/11/2009, 14:30 — 15:30 — Room P3.10, Mathematics Building

Camille Laurent, *University of Coimbra*

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Introduction to Abelian and non-Abelian gerbes

We shall use the language of Lie groupoids and Morita equivalence to introduce gerbes, and connections on them. The advantage of this presentation is that it makes it possible to use ordinary differential geometry, without going to "higher" objects - the default being the need to check the invariance of all constructions under Morita equivalence. I shall try to relate this construction with previous ones, especially the constructions of Breen and Messing.

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04/12/2008, 16:30 — 17:30 — Room P3.10, Mathematics Building

Tim Porter, *University of Wales, Bangor, UK*

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The "Crossed" technology and its applications - IV

(see Lecture 1)

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04/12/2008, 14:30 — 15:30 — Room P3.10, Mathematics Building

Tim Porter, *University of Wales, Bangor, UK*

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The "Crossed" technology and its applications - III

(see Lecture 1)

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03/12/2008, 16:30 — 17:30 — Room P3.10, Mathematics Building

Tim Porter, *University of Wales, Bangor, UK*

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The “Crossed” technology and its applications - II

(see Lecture 1)

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03/12/2008, 11:30 — 12:30 — Room P3.10, Mathematics Building

Tim Porter, *University of Wales, Bangor, UK*

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The “Crossed” technology and its applications

In this short series of lectures I will introduce crossed modules and crossed complexes, both algebraically and topologically, will look at their relevance for combinatorial group theory, the theory of syzygies and group cohomology, and then will head for higher order objects namely 2-crossed modules, and related complexes. In the final parts I will introduce some of the constructions of non-Abelian cohomology, sheaves, torsors and Bitorsors and consider the interaction between the crossed gadgetry of the earlier lectures and this area. ##### References

- The pdf file at the start of the following page, which includes discussions: n-Category Café
- Slightly updated version of the crossed menagerie file: Crossed Menagerie

Schedule:

Lecture 1: Wednesday, 3rd December, 2008, 11h30 - 13

Lecture 2: Wednesday, 3rd December, 2008, 16h30 - 18

Lecture 3: Thursday, 4th December, 2008, 14h30 - 16

Lecture 4: Thursday, 4th December, 2008, 16h30 - 18

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14/07/2008, 11:30 — 12:30 — Room P3.10, Mathematics Building

John Baez, *Department of Mathematics, University of California at Riverside*

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Topological 2-Groups and Their Classifying Spaces

Categorifying the concept of topological group, one obtains the notion of a topological 2-group. This in turn allows a theory of "principal 2-bundles" generalizing the usual theory of principal bundles. It is well-known that under mild conditions on a topological group $G$ and a space $M$, principal $G$-bundles over $M$ are classified by either the Cech cohomology ${H}^{1}(M,G)$ or the set of homotopy classes $[M,BG]$, where $BG$ is the classifying space of $G$. Here we review work by Bartels, Jurco, Baas-Bökstedt-Kro, and others generalizing this result to topological 2-groups. We explain various viewpoints on topological 2-groups and the Cech cohomology ${H}^{1}(M,G)$ with coefficients in a topological 2-group $G$, also known as "nonabelian cohomology". Then we sketch a proof that under mild conditions on $M$ and $G$ there is a bijection between ${H}^{1}(M,G)$ and $[M,B\mid G\mid ]$, where $B\mid G\mid $ is the classifying space of the geometric realization of the nerve of $G$. Applying this result to the ''string 2-group" $\mathrm{String}(G)$ of a simply-connected compact simple Lie group $G$, we obtain a theory of characteristic classes for principal $\mathrm{String}(G)$-2-bundles.

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14/07/2008, 10:00 — 11:00 — Room P3.10, Mathematics Building

Louis Kauffman, *Department of Mathematics, Statistics, and Computer Science, University of Illinois at Chicago*

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Virtual Knot Theory

New developments in Virtual Knot Theory.