A graph in R^n is a closed subset that locally looks like R (edges) or like a wedge of half intervals (vertices). I will describe a topology on the space of all such graphs and determine its homotopy type. This is one step in determining the homology of Aut(F_n), the automorphism group of a free group, in the limit where n goes to infinity.
A 2-dimensional Topological Quantum Field Theory (TQFT) is a symmetric monoidal functor from the category of 2-dimensional cobordisms to the category of vector spaces. A classic result states that 2d TQFTs are classified by commutative Frobenius algebras. I show how to extend this result to open-closed TQFTs using a class of 2-manifolds with corners, how to use the Moore-Segal relations in order to find a canonical form and a complete set of invariants for our cobordisms and how to classify open-closed TQFTs algebraically. Open-closed TQFTs can be used to find algebraic counterparts of Bar-Natan's topological extension of Khovanov homology from links to tangles and in order to get hold of the braided monoidal 2-category that governs this aspect of Khovanov homology. I also sketch what open-closed TQFTs reveal about the categorical ladder of combinatorial manifold invariants according to Crane and Frenkel.
references:
1] A. D. Lauda, H. Pfeiffer:
Open-closed strings: Two-dimensional extended TQFTs and Frobenius algebras,
Topology Appl. 155, No. 7 (2008) 623-666, arXiv:math/0510664
2] A. D. Lauda, H. Pfeiffer: State sum construction of two-dimensional open-closed Topological Quantum Field Theories,
J. Knot Th. Ramif. 16, No. 9 (2007) 1121-1163,arXiv:math/0602047
3] A. D. Lauda, H. Pfeiffer: Open-closed TQFTs extend Khovanov homology from links to tangles, J. Knot Th. Ramif., in press, arXiv:math/0606331.
Mean curvature vector is the negative gradient of the area functional. Thus if we deform a submanifold along its mean curvature vector, which is called mean curvature flow (MCF), the area will decrease most rapidly. When the ambient manifold is Kahler-Einstein, being Lagrangian is preserved under MCF. It is thus very natural trying to construct special Lagrangian/ Lagrangian minimal through MCF. In this talk, I will make a brief introduction and report some of my recent works with my coauthors in this direction, which mainly concern the singularities of the flow.
The birational classification of varieties is an interesting and ongoing problem in algebraic geometry. This talk aims to give an
overview of the progress made on this problem in the special case where the varieties considered are surfaces in projective space.
I will start by reviewing the current status of the stability
problem for black holes in general relativity. In the second part of the
talk I will focus on a particular (symmetry) class of five-dimensional
dynamical black holes recently introduced by Bizon et al as a model to
study gravitational collapse in vacuum. In this context I state a recent
result establishing the asymptotic stability of the five dimensional
Schwarzschild metric with respect to vacuum perturbations in the given
class.