# Seminário de Teoria Quântica do Campo Topológica

## Sessões anteriores

Páginas de sessões mais recentes: Seguinte 2 1 Mais recente

### 30/11/2015, 11:30 — 12:30 — Sala P3.10, Pavilhão de Matemática

Roger Picken, *Instituto Superior Técnico*

### Actions of 2-groups, moduli spaces in higher gauge theory, and TQFT's

In the context of higher gauge theory (HGT) based on a 2-group, I will discuss how the language of double categories provides a natural description of 2-group actions on a category. One of the motivations is to understand moduli spaces of flat connections modulo gauge transformations in HGT, and this goal is achieved for some simple manifolds. I will also relate these ideas to a class of Topological Quantum Field Theories (TQFT's) for surfaces, obtained from finite groups and 2-groups.

This talk is based on callaborations with João Faria Martins, Jeffrey Morton and Diogo Bragança. It is also intended as preparation for the visit by Urs Schreiber, 15 Jan—14 Feb, 2016.

### 23/10/2015, 11:30 — 12:30 — Sala P3.10, Pavilhão de Matemática

Benjamin Alarcón Heredia, *Universidade Nova de Lisboa*

### Bicategories, classifying spaces and homotopy pullbacks

In this continuation of my last talk I will give an introduction to the homotopy theory of bicategories. First I will present the way to convert bicategories to spaces, and then I will use this to describe homotopy pullbacks of homomorphisms of bicategories.

### 09/10/2015, 11:30 — 12:30 — Sala P3.10, Pavilhão de Matemática

Benjamin Alarcón Heredia, *Universidade Nova de Lisboa*

### Homotopy theory using categories

This is an introductory talk about the homotopy theory of categories. I will present the classifying space of a category and the classical results of Thomason and Quillen for obtaining categorical descriptions of homotopy colimits and homotopy pullbacks.

### 01/10/2015, 11:30 — 12:30 — Sala P3.10, Pavilhão de Matemática

Igor Salom, *Institute of Physics, Belgrade, Serbia*

### Positive energy unitary irreducible representations of $\operatorname{osp}(1|2n)$ superalgebras

Orthosymplectic $\operatorname{osp}(1|2n)$ superalgebras are being considered as alternatives to $d$-dimensional Poincaré/conformal superalgebras and thus have significant potential relevance in various subfields of High Energy Physics and Astrophysics. Yet, due to mathematical difficulties, even the classification of their unitary irreducible representations (UIR's) has not been entirely accomplished. This is also true for the physically most important subclass of *positive energy* UIR's.

In this talk I will first demonstrate this classification for the $n=4$ case (that corresponds to four dimensional space-time). The classification is obtained by careful analysis of the Verma module structure, which is particularly subtle due to the existence of subsingular vectors. Based on these results I will then conjecture their generalization to the case of arbitrary $n$ (thus also including cases relevant in the string/brane context). In addition, I will show an elegant explicit realization of these UIR's that exists for (half)integer values of the conformal energy and that makes manifest the mathematical connection existing between UIR's of orthogonal and orthosymplectic algebras. The existence of this realization, per se, proves a part of the conjecture.

### 17/09/2015, 16:30 — 17:30 — Sala P3.10, Pavilhão de Matemática

Jedrzej Swiezewski, *University of Warsaw*

### Geometrical diffeomorphism invariant observables for General Relativity and their applications

During the talk I will present a recent construction of observables for General Relativity invariant under spatial diffeomorphisms. The construction involves introducing a local structure representing the "observer" (based on arXiv:1403.8062). I will also present how those observables can be used to reduce the phase space of canonical General Relativity (based on arXiv:1506.09164).

If time permits, I will argue that the construction is particularly useful in spherically symmetric situations. This realization lead to a proposal of a scheme of reducing Loop Quantum Gravity to its spherically symmetric sector, which completes the standard, midisuperspace approach (based on arXiv:1410.5609).

#### Ver também

swiezewski.pdf

### 15/06/2015, 11:30 — 12:30 — Sala P3.10, Pavilhão de Matemática

Kishore Marathe, *City University of New York*

### Physical Mathematics: old and new

In this talk we will discuss some topics related to the interaction of physical and mathematical theories that have led to new points of view and new results in mathematics. The area where this is most evident is that of geometric topology of low dimensional manifolds. I coined the term *Physical Mathematics* to describe this new and fast growing area of research and used it in the title of my paper in Springer's book *Mathematics Unlimited: 2001 and beyond*.

We will discuss some recent developments in this area. General reference for this talk is my book *Topics in Physical Mathematics*, Springer (2010).

### 22/04/2015, 16:00 — 17:00 — Sala P3.10, Pavilhão de Matemática

Daniele Pranzetti, *University of Erlangen-Nürnberg*

### Black hole entropy in loop quantum gravity

After briefly introducing the main ingredients of the loop quantum gravity approach, I show how it can applied to the calculation of black hole entropy. I review some well known results and open issues resulting from the interplay with Chern-Simons theory techniques. I then introduce a new analysis of the horizon degrees of freedom in terms of purely LQG methods, which turns out to be dual to a CFT description. I show how this unifying framework allows us to recover the semiclassical Bekenstein-Hawking entropy formula.

#### Ver também

Pranzetti_Black_Hole_in_Loop_Quantum_Gravity_Slides_20150422.pdf

### 25/03/2015, 16:00 — 17:00 — Sala P3.10, Pavilhão de Matemática

Marko Vojinovic, *Grupo de Fisica Matematica, Univ. Lisboa*

### Introduction to Loop Quantum Gravity (part 3)

This series of lectures is intended to give an elementary introduction to the topic of the canonical quantization of the gravitational field, in the context of the Loop Quantum Gravity approach.

In the third lecture we will finish the construction of the spin-knot space and introduce the loop transform. Then we move on to the analysis of geometric observables (distance, area and volume) and the structure of the scalar constraint. Finally, matter coupling will be introduced. If time permits, we will also give a short review of two applications of the formalism: calculation of the black hole entropy, and the Big Bounce model of Loop Quantum Cosmology.

### 18/03/2015, 16:00 — 17:00 — Sala P3.10, Pavilhão de Matemática

Marko Vojinovic, *Grupo de Fisica Matematica, Univ. Lisboa*

### Introduction to Loop Quantum Gravity (part 2)

This series of lectures is intended to give an elementary introduction to the topic of the canonical quantization of the gravitational field, in the context of the Loop Quantum Gravity approach.

The second lecture is devoted to the canonical quantization procedure within the LQG framework. We will begin by a short introduction to the notion of background independence, and differences between perturbative and nonperturbative quantization. We will then rewrite general relativity in the canonical space+time formulation and introduce Ashtekar variables, as preparation for the canonical quantization. Then the main step is the quantization itself, and the construction of the appropriate Hilbert space of the theory based on the notions of spin networks and spin-knots.

### 04/03/2015, 15:30 — 16:30 — Sala P3.10, Pavilhão de Matemática

Marko Vojinovic, *Grupo de Fisica Matematica, Univ. Lisboa*

### Introduction to Loop Quantum Gravity (part 1)

This series of lectures is intended to give an elementary introduction to the topic of the canonical quantization of the gravitational field, in the context of the Loop Quantum Gravity approach.

The first lecture will be devoted to the formulation of the problem of quantization of the gravitational field. We will give an overview of perturbative quantization, discuss the issue of nonrenormalizability, and provide a general classification of most prominent approaches to constructing a theory of quantum gravity. One such approach is Loop Quantum Gravity, which will be studied in more detail in subsequent lectures.

### 26/02/2015, 11:30 — 12:30 — Sala P3.10, Pavilhão de Matemática

Saikat Chatterjee, *Institut des Hautes Études Scientifiques, France*

### Twisted actions of categorical groups

We develop a theory of twisted actions of categorical groups using the notion of semidirect product of categories. I will present many examples of semi-direct product of categories. If time permits I will also work-out an example of twisted action involving the Poincaré 2-group. Specializing to the case of representations, where the the category on which categorical group acts has some kind of a vector space structure, we will establish a categorical analogue of Schur's lemma.

This is a joint work with A. Lahiri and A. Sengupta.

### 17/06/2014, 11:30 — 12:30 — Sala P3.10, Pavilhão de Matemática

Travis Willse, *The Australian National University, Canberra*

### Holography for parallel conformal data

The Fefferman-Graham ambient metric construction, with some technical asterisks, positively resolves the Dirichlet problem for compactification of asymptotically hyperbolic Einstein metrics, the compactification that occurs in the AdS/CFT correspondence. We show that data on the conformal boundary parallel with respect to Cartan's normal conformal connection — which is nearly the same thing as a holonomy reduction of the conformal structure — can be extended (again with an asterisk) to data parallel with respect to a natural connection on a corresponding bundle over the bulk, which in particular enables holographic study of such data. As an application, we use this extension result to construct metrics of exceptional holonomy.

### 27/05/2014, 14:30 — 15:30 — Sala P3.10, Pavilhão de Matemática

Jonathon Funk, *University of the West Indies, Barbados*

### Grothendieck topologies for C*-algebras

We investigate a (contravariant) functor from C*-algebras to
toposes and geometric morphisms that generalizes the Gelfand
spectrum in the commutative case. The functor produces a locale,
presented by means of a Grothendieck topology on an inf-semilattice
of 'Gelfand' opens \([U;a]\).

### 27/05/2014, 13:30 — 14:30 — Sala P3.10, Pavilhão de Matemática

Andreas Döring, *Friedrich-Alexander-Universität Erlangen-Nürnberg*

### The Spectral Presheaf as the Spectrum of a Noncommutative Operator
Algebra

The spectral presheaf of a nonabelian von Neumann algebra or
C*-algebra was introduced as a generalised phase space for a
quantum system in the so-called topos approach to quantum theory.
Here, it will be shown that the spectral presheaf has many features
of a spectrum of a noncommutative operator algebra (and that it can
be defined for other classes of algebras as well). The main idea is
that the spectrum of a nonabelian algebra may not be a set, but a
presheaf or sheaf over the base category of abelian subalgebras. In
general, the spectral presheaf has no points, i.e., no global
sections. I will show that there is a contravariant functor from
the category of unital C*-algebras to a category of presheaves that
contains the spectral presheaves, and that a C*-algebra is
determined up to Jordan *-isomorphisms by its spectral presheaf in
many cases. Moreover, time evolution of a quantum system can be
described in terms of flows on the spectral presheaf, and
commutators show up in a natural way. I will indicate how combining
the Jordan and Lie algebra structures can lead to a full
reconstruction of nonabelian C*- or von Neumann algebra from its
spectral presheaf.

### 26/05/2014, 15:30 — 16:30 — Sala P3.10, Pavilhão de Matemática

Paolo Bertozzini, *Thammasat University, Bangkok, Thailand*

### Higher Categories of Operator Algebras

A satisfactory marriage between “higher” categories and
operator algebras has never been achieved: although (monoidal)
C*-categories have been systematically used since the development
of the theory of superselection sectors, higher category theory has
more recently evolved along lines closer to classical higher
homotopy.

We present axioms for strict involutive \(n\)-categories (a
vertical categorification of dagger categories) and a definition
for strict higher C*-categories and Fell bundles (possibly equipped
with involutions of arbitrary depth), that were developed in
collaboration with Roberto Conti, Wicharn Lewkeeratiyutkul and
Noppakhun Suthichitranont.

In order to treat some very natural classes of examples arising
from the study of hypermatrices and hyper-C*-algebras, that would
be otherwise excluded by the standard Eckmann-Hilton argument, we
suggest a non-commutative version of exchange law and we also
explore alternatives to the usual globular and cubical
settings.

Possible applications of these non-commutative higher
C*-categories are envisaged in the algebraic formulation of
Rovelli's relational quantum theory, in the study of morphisms in
Connes' non-commutative geometry, and in our proposed “modular”
approach to quantum gravity (arXiv: 1007.4094).

### 14/05/2014, 16:00 — 17:00 — Sala P4.35, Pavilhão de Matemática

Sara Tavares, *University of Nottingham, United Kingdom*

### Two-dimensional state sum models and spin structures

Topological field theories are very special in two dimensions:
they have been classified and provide a rich class of examples. In
this talk I will discuss a new state sum construction for these
models that considers not just the topology of surfaces but also
their spin structure. Emphasis is given to partition functions: I
will detail general properties of these manifold invariants and
discuss some non-trivial examples.

### 02/04/2014, 16:00 — 17:00 — Sala P4.35, Pavilhão de Matemática

Aleksandar Mikovic, *Universidade Lusófona and Grupo de Física Matemática*

### 2-BF Theories

We will describe 2-BF topological field theories, which are
categorical generalization of the BF theories. We will also explain
how to construct invariants of manifolds by using 2-BF theory path
integrals.

#### References

- João Faria Martins, Aleksandar Mikovic,. Lie crossed modules and
gauge-invariant actions for 2-BF theories. Adv. Theor. Math.
Phys. Volume 15, Number 4, 1059-1084 (2011).
- Aleksandar Mikovic, Marko Vojinovic, Poincaré 2-group and quantum
gravity,. Class. Quant. Grav. 29, 165003 (2012).

### 01/04/2014, 11:30 — 12:30 — Sala P3.10, Pavilhão de Matemática

Zoran Škoda, *University of Zagreb*

### Coherent states for quantum groups

Quantum groups at roots of unity appear as hidden symmetries in
some conformal field theories. For this reason I. Todorov has (in
1990s) used coherent state operators for quantum groups to
covariantly build the field operators in Hamiltonian formalism. I
tried to mathematically found his coherent states by an analogy
with the Perelomov coherent states for Lie groups. For this, I use
noncommutative localization theory to define and construct the
noncommutative homogeneous spaces, and principal and associated
bundles over them. Then, in geometric terms, I axiomatize the
covariant family of coherent states which enjoy a resolution of
unity formula, crucial for physical applications. Even the simplest
case of quantum \(\operatorname{SL2}\) is rather involved and the
corresponding resolution of unity formula involves the Ramanujan's
\(q\)-beta integral. The correct covariant family differs from ad
hoc proposed formulas in several published papers by earlier
authors.

#### Ver também

lispr1.pdf

### 12/03/2014, 16:00 — 17:00 — Sala P4.35, Pavilhão de Matemática

Marko Vojinovic, *Grupo de Fisica Matemática, Universidade de Lisboa*

### Introduction to renormalization in QFT (part III)

In the previous talk we discussed the renormalization procedure on
the example ${\varphi}^{4}$ scalar field theory. In this lecture we will
conclude the analysis of that example, construct the final
renormalized state sum, and discuss the renormalization group
equations. At the end we will give some final general remarks about
renormalization in QFT.

#### Ver também

https://math.tecnico.ulisboa.pt/seminars/download.php?fid=9

### 26/02/2014, 16:00 — 17:00 — Sala P4.35, Pavilhão de Matemática

John Huerta, *IST, Lisbon*

### What can higher categories do for physics? Part II

In this follow up to last year's talk, we briefly review the
cobordism hypothesis that formed the subject of our first part, and
then outline its use for the existence and construction of field
theories, in particular Chern-Simons theory, as discussed in a 2009
paper of Freed, Hopkins, Lurie and Teleman.

Páginas de sessões mais antigas: Anterior 4 5 6 7 8 9 10 11 12 Mais antiga

Organizadores correntes: Roger Picken, Marko Stošić.

Projecto FCT PTDC/MAT-GEO/3319/2014, *Quantization and Kähler Geometry*.