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09/05/2012, 14:00 — 16:00 — Room P3.10, Mathematics Building

Marco Mackaay, *Univ. Algarve*

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\(\mathfrak{sl}_3\) web algebras

This is joint work with Weiwei Pan and Daniel Tubbenhauer from
Gottingen University, Germany.

First of two talks in an Informal Categorication Afternoon about current research projects in the area of categorification.

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12/01/2012, 11:30 — 12:30 — Room P12, Mathematics Building

Jeffrey C. Morton, *Instituto Superior Técnico*

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Groupoidification and Khovanov's Categorification of the Heisenberg Algebra

The aim of this talk is to describe the connection between two approaches to categorification of the Heisenberg algebra. The groupoidification program of Baez and Dolan has been used to give a representation of the quantum harmonic oscillator in the category Span(Gpd) where the Fock space is represented by the groupoid of finite sets and bijections. This naturally gives a combinatorial interpretation of the (one-variable) Heisenberg algebra in the endomorphisms of this groupoid. On the other hand, Khovanov has given a categorification in which the integral part of the (many variable) Heisenberg algebra is recovered as the Grothendieck ring of a certain monoidal category described in terms of a calculus of diagrams. I will describe how an extension of the groupoidification program to a 2-categorical form of Span(Gpd) recovers the relations used by Khovanov's construction, and how to interpret them combinatorially in terms of the groupoid of finite sets.

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06/01/2012, 16:00 — 17:00 — Room P3.10, Mathematics Building

Nuno Freitas, *Universitat de Barcelona*

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From Fermat's Last Theorem to some generalized Fermat equations

The proof of Fermat's Last Theorem was initiated by Frey,
Hellegouarch, Serre, further developed by Ribet and ended with
Wiles' proof of the Shimura-Tanyama conjecture for semi-stable
elliptic curves. Their strategy, now called the modular approach,
makes a remarkable use of elliptic curves, Galois representations
and modular forms to show that ${a}^{p}+{b}^{p}={c}^{p}$ has no solutions,
such that $(a,b,c)=1$ if $p\ge 3$. Over the last 17 years, the
modular approach has been continually extended and allowed people
to solve many other Diophantine equations that previously seemed
intractable. In this talk we will use the equation ${x}^{p}+{2}^{\alpha}{y}^{p}={z}^{p}$ as the motivation to introduce informally the
original strategy ($\alpha =0$) and illustrate one of its first
refinements (for $\alpha =1$). Then we will discuss some further
generalizations that recently led to the solution of equations of
the form ${x}^{5}+{y}^{5}=d{z}^{p}$.

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06/12/2011, 15:00 — 16:00 — Room P3.10, Mathematics Building

John Huerta, *Australian National University, Canberra*

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Superstrings, higher gauge theory, and division algebras

Recent work on higher gauge theory suggests the presence of 'higher symmetry' in superstring theory. Just as gauge theory describes the physics of point particles using Lie groups, Lie algebras and bundles, higher gauge theory is a generalization that describes the physics of strings and membranes using categorified Lie groups, Lie algebras and bundles. In this talk, we will summarize the mathematics of a higher gauge theory. We then show how to construct the categorified Lie algebras relevant to superstring theory by a systematic use of the normed division algebras. At the end, we will touch on how this leads to a categorified supergroup extending the Poincare supergroup in the mysterious dimensions where the classical superstring makes sense — 3, 4, 6 and 10.

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09/11/2011, 14:00 — 15:00 — Room P4.35, Mathematics Building

Pedro Vaz, *Instituto Superior Técnico*

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Categorified $q$-Schur algebra and the BMW algebra

In 1989 François Jaeger showed that the the Kauffman polynomial of a link $L$ can be obtained as a weighted sum of HOMFLYPT polynomials on certain links associated to $L$. In this talk I will explain how to use a version of Jaeger's theorem to stablish a connection between the $\mathrm{SO}(2N)-\mathrm{BMW}$ and the $q$-Schur algebras. I will then present a subcategory of the Schur category which categorifies the $\mathrm{SO}(2N)-\mathrm{BMW}$ algebra (joint with E. Wagner).

Support: FCT, CAMGSD, New Geometry and Topology.. (Room P4.35 still to be confirmed)

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28/10/2011, 10:30 — 11:30 — Room P3.10, Mathematics Building

Jeffrey Morton, *Instituto Superior Técnico*

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Extended TQFT in a Bimodule 2-Category

I will describe an extended (2-categorical) topological QFT with target 2-category consisting of C*-algebras and bimodules. The construction is explained as factorizable into a classical field theory valued in groupoids, and a quantization functor, as in the program of Freed-Hopkins-Lurie-Teleman. I will explain the Lagrangian action functional in terms of cohomological twisting of the groupoids in the classical part of the theory, and describe how this is incorporated into the quantization functor. This project is joint work with Derek Wise.

Support: FCT, CAMGSD, New Geometry and Topology

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28/07/2011, 15:30 — 16:30 — Room P3.10, Mathematics Building

Andreas Döring, *Univ. of Oxford*

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Towards Noncommutative Gel'fand Duality

Gel'fand-Naimark duality (1943) between the categories of unital commutative ${C}^{*}$-algebras and compact Hausdorff spaces is a key insight of 20th century mathematics, providing an enormously useful bridge between algebra on the one hand and topology and geometry on the other. Many generalisations and related dualitites exist, in logical, localic and constructive forms. Yet, all this is for *commutative* algebras (and distributive lattices of projections, or opens), while in quantum theory and in a large variety of mathematical situations, *noncommutative* algebras play a central role. A good, generally useful notion of spectra of noncommutative algebras is still lacking. Clearly, such spectra will be of considerable interest for physics and Noncommutative Geometry. I will report on recent progress towards defining spectra of noncommutative operator algebras, mostly for von Neumann algebras. This work comes from the approach using topos theory to reformulate quantum physics (C. Isham, AD), where a presheaf or sheaf topos is assigned to each noncommutative operator algebra, together with a distinguished spectral object. It will be shown that this assignment is functorial, and that the spectral object determines the algebra up to Jordan isomorphisms (J. Harding, AD). Progress on characterising the action of the unitary group of an algebra - relating to Lie group and Lie algebra aspects - is presented. Moreover, recently established connections with Zariski geometries from geometric model theory will be sketched (B. Zilber, AD). This is joint work with John Harding, Boris Zilber, and Chris Isham.

FCT, CAMGSD, New Geometry and Topology.

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28/07/2011, 14:00 — 15:00 — Room P3.10, Mathematics Building

Yasuyoshi Yonezawa, *Univ. of Bonn*

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A specialized Kauffman polynomial using 4-valent planar diagrams

I want to discuss about specialized Kauffman polynomial using 4-valent planar diagrams. A problem is can we categorify this polynomial.

FCT, CAMGSD, New Geometry and Topology.

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13/07/2011, 15:30 — 16:30 — Room P3.10, Mathematics Building

João Faria Martins, *Univ. Nova de Lisboa*

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Categorifying the Knizhnik-Zamolodchikov connection

(Joint with Lucio Simone Cirio, Max Planck Institute for Mathematics)

In the context of higher gauge theory, we categorify the Knizhnik-Zamolodchikov connection in the configuration space of $n$ particles in the complex plane by means of a differential crossed module of (totally symmetric) horizontal 2-chord diagrams, categorifying the 4-term relation.

We carefully discuss the representation theory of differential crossed modules in chain-complexes of vector spaces, inside which we formulate the notion of infinitesimal 2-R matrix, an infinitesimal counterpart of some of the relations satisfied by braid cobordisms.

We present several open problems.

FCT, CAMGSD, New Geometry and Topology.

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13/07/2011, 14:00 — 15:00 — Room P3.10, Mathematics Building

Stephen Huggett, *University of Plymouth*

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Seifert graphs, Eulerian subgraphs, and partial duality

I will describe how to characterize the Seifert graphs of link diagrams, and how, using the notion of partial duality in ribbon graphs, this leads to a generalization of the classical result that a plane graph is Eulerian if and only if its geometric dual is bipartite. This is joint work with Iain Moffatt and Natalia Virdee.

FCT, CAMGSD, New Geometry and Topology.

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08/06/2011, 16:30 — 17:30 — Room P3.10, Mathematics Building

Marco Mackaay, *Univ. of the Algarve*

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The Schur quotient of the Khovanov-Lauda categorification of quantum ${\mathrm{sl}}_{n}$ and colored HOMFLY homology

In my talk I will first remind everyone of the relation between quantum $\mathrm{sln}$, the $q$-Schur algebra and colored HOMFLY homology. After that I will explain how these objects and the relation between them have been categorified.

Support: FCT, CAMGSD, New Geometry and Topology

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08/06/2011, 15:00 — 16:00 — Room P3.10, Mathematics Building

Alistair Savage, *Univ. of Ottawa, Canada*

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Hecke algebras and a categorification of the Heisenberg algebra

In this talk, we will present a graphical category in terms of certain planar braid-like diagrams. The definition of this category is inspired by the representation theory of Hecke algebras of type A (which are certain deformations of the group algebra of the symmetric group). The Heisenberg algebra (in infinitely many generators), which plays an important role in the description of certain quantum mechanical systems, injects into the Grothendieck group of our category, yielding a "categorification" of this algebra. We will also see that our graphical category acts on the category of modules of Hecke algebras and of general linear groups over finite fields. Additionally, other algebraic structures, such as the affine Hecke algebra, appear naturally.

We will assume no prior knowledge of Hecke algebras or the Heisenberg algebra. The talk should be accessible to graduate students. This is joint work with Anthony Licata and inspired by work of Mikhail Khovanov.

Support: FCT, CAMGSD, New Geometry and Topology.

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04/02/2011, 16:00 — 17:00 — Room P3.10, Mathematics Building

Sebastian Guttenberg, *Instituto Superior Técnico*

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A short introduction to string theory II

This will be a very introductory (and informal) mini-course on string theory. No prior exposure to string theory will be expected. Although I will use physicists language, the course is mainly addressed at math-students / postdocs who are welcome to help me translating expressions into math-language during the lectures. I will try to make at least some connection to higher gauge fields and also say a few words on how non-commutative geometry arises from open strings. In the first session I will concentrate on the bosonic string, while in the second I intend to discuss the superstring.

Room QA1.2 Torre Sul

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04/02/2011, 14:30 — 15:30 — Room P3.10, Mathematics Building

Aleksandar Mikovic, *Univ. Lusófona*

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Quantum gravity and spin foams II

In the first lecture I will explain what is the problem of quantum gravity from a physics and a mathematics perspective. In the second lecture I will concentrate on the spin foam approach and explain its basic features.

Room QA1.2 Torre Sul

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02/02/2011, 16:00 — 17:00 — Room P3.10, Mathematics Building

Sebastian Guttenberg, *Instituto Superior Técnico*

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A short introduction to string theory I

This will be a very introductory (and informal) mini-course on string theory. No prior exposure to string theory will be expected. Although I will use physicists language, the course is mainly addressed at math-students / postdocs who are welcome to help me translating expressions into math-language during the lectures. I will try to make at least some connection to higher gauge fields and also say a few words on how non-commutative geometry arises from open strings. In the first session I will concentrate on the bosonic string, while in the second I intend to discuss the superstring.

Room QA1.4 Torre Sul

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02/02/2011, 14:30 — 15:30 — Room P3.10, Mathematics Building

Aleksandar Mikovic, *Univ. Lusófona*

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Quantum gravity and spin foams I

In the first lecture I will explain what is the problem of quantum gravity from a physics and a mathematics perspective. In the second lecture I will concentrate on the spin foam approach and explain its basic features.

Room QA1.4 Torre Sul

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26/01/2011, 14:30 — 15:30 — Room P3.10, Mathematics Building

Tomasz Brzezinski, *Department of Mathematics, University of Wales Swansea, UK*

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Toward synthetic noncommutative geometry

In the first part of the talk we outline the basic ideas of synthetic approach to differential geometry. The main idea of this approach, which originates from considerations of Sophus Lie is very simple: All geometric constructions are performed within a suitable base category in which space forms are objects. In the second part we indicate how a synthetic method could be employed in the context of Noncommutative Differential Geometry.

This talk is addressed to mathematicians who have some very basic familiarity with general category theory culture and are familiar with elementary concepts of geometry and algebra. The aim is to explain synthetic approach to commutative and noncommutative geometry on two examples of geometric notions. First we explain all categorical ingredients that enter the synthetic definition of a principal bundle (in classical geometry) and then we show that noncommutative generalisation of this definition yields in particular principal comodule algebras or faithfully flat Hopf-Galois extensions.

This seminar is transmitted by videoconference from Oporto

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19/01/2011, 15:00 — 16:00 — Room P3.10, Mathematics Building

Benjamin Himpel, *Aarhus University*

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The asymptotic expansion of the Witten-Reshetikhin-Turaev invariants

Witten's influential invariants for links in 3-manifolds given in terms of a non-rigorous Feynman path integral have been rigorously defined first by Reshetikhin and Turaev. Their combinatorial definition based on the axioms of topological quantum field theory is expected to have an asymptotic expansion in view of the perturbation theory of Witten's path integral with leading order term (the semiclassical approximation) given by formally applying the method of stationary phase. Furthermore, the terms in this asymptotic expansion are expected to be well-known classical invariants like the Chern-Simons invariant, spectral flow, the Rho invariant and Reidemeister torsion. I will present new results on the expansion for finite order mapping tori, whose leading order terms we identified with classical topological invariants. Joint with Jørgen E. Andersen.

Support: FCT, CAMGSD, New Geometry and Topology.

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15/12/2010, 15:15 — 16:15 — Room P3.10, Mathematics Building

Gonçalo Rodrigues, *Instituto Superior Técnico*

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Categorifying Measure Theory II

This lecture will be a continuation of my October lecture on a program to categorify measure theory. After a quick reminder of some of the basic concepts like the finite Grothendieck topology and cosheaves, and the basic theorem on the (bi)representability of the the cosheaf category, I will try to demonstrate that all the work gone into setting up the machinery was not in vain by first, giving categorified versions of some basic theorems of measure theory (e.g. Fubini and Fubini-Tonelli) and second, by explaining some of the rich structure underlying categorified measure theory, a blend of analysis, algebraic geometry and topos theory.

Support: FCT, CAMGSD, New Geometry and Topology

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10/11/2010, 15:30 — 16:30 — Room P3.10, Mathematics Building

Björn Gohla, *Univ. Porto*

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Tri-connections and trifunctors

It is well known that connections on a principal G-bundle over a manifold M can be represented by group homomorphisms LM->G, where LM is the loop group of M. Similarly, 2-connections can be seen as 2-functors from a 2-groupoid of points, paths and bigons in M to a 2-group G. In passing to dimension 3, that is, considering tri-connections, 3-groupoids are too rigid, instead one needs to consider Gray-groupoids, their morphisms and transformations of higher dimension. We will describe a groupoid structure for certain functors between a pair of Gray-categories and certain transformations between them.

Support: FCT, CAMGSD, New Geometry and Topology.