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Series: Geometry Topology Seminar

The mapping class group of the plane minus a Cantor set naturally appears in many dynamical contexts, including group actions on surfaces, the study of groups of homeomorphisms on a Cantor set, and complex dynamics. In this talk, I will present the 'ray graph', which is a Gromov-hyperbolic graph on which this big mapping class group acts by isometries (it is an equivalent of the curve graph for this surface of infinite topological type). If time allows, I will give a description of the Gromov-boundary of the ray graph in terms of long rays in the plane minus a Cantor set. This involves joint work with Alden Walker.

Series: Geometry Topology Seminar

We will give different topological very simple statements that seem not to have been noticed, although they are of the level
of Brouwer’s fixed point theorem. The main result is: Let F be a compact subset of the manifold M. Assume g:F->M is a continuous map which is the identity on the boundary (or frontier) of F, then the image g(F) contains either F or M\F.

Series: Geometry Topology Seminar

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Series: Geometry Topology Seminar

Series: Geometry Topology Seminar

There has been a recent interest in studying surfaces of infinite type, i.e. surfaces with infinitely-generated fundamental groups. In this talk, we will focus on their mapping class groups, often called big mapping class groups. In contrast to the finite-type case, there are many open questions regarding the basic algebraic and topological properties of big mapping class groups. I will discuss several such questions and provide some answers. In particular, I will discuss automorphism groups of mapping class groups as well as relations between topological invariants of a surface and algebraic invariants of its mapping class group. The results in the talk are based on recent joint work with Priyam Patel and ongoing joint work with Javier Aramayona and Priyam Patel.

Series: Geometry Topology Seminar

I will talk about homomorphisms between surface braid groups. Firstly, we will see that any surjective homomorphism from PB_n(S) to PB_m(S) factors through a forgetful map. Secondly, we will compute the
automorphism group of PB_n(S). It turns out to be the mapping class group when n>1.

Series: Geometry Topology Seminar

Certain fibered hyperbolic 3-manifolds admit a layered veering triangulation, which can be constructed algorithmically given the stable lamination of the monodromy. These triangulations were introduced by Agol in 2011, and have been further studied by several others in the years since. We present experimental results which shed light on the combinatorial structure of veering triangulations, and its relation to certain topological invariants of the underlying manifold. We will begin by discussing essential background material, including hyperbolic manifolds and ideal triangulations, and more particularly fibered hyperbolic manifolds and the construction of the veering triangulation.

Series: Geometry Topology Seminar

We give a simple geometric criterion for an element to normally generate the mapping class group of a surface. As an application of this criterion, we show that when a surface has genus at least 3, every periodic mapping class except for the hyperelliptic involution normally generates. We also give examples of pseudo-Anosov elements that normally generate when genus is at least 2, answering a question of D. Long.

Series: Geometry Topology Seminar

We will discuss a relation between some notions in three-dimensional topology and four-dimensional aspects of knot theory.

Series: Geometry Topology Seminar

Alexandru Oancea:
Title: Symplectic homology for cobordisms
Abstract: Symplectic homology for a Liouville cobordism - possibly filled
at the negative end - generalizes simultaneously the symplectic homology of
Liouville domains and the Rabinowitz-Floer homology of their boundaries. I
will explain its definition, some of its properties, and give a sample
application which shows how it can be used in order to obstruct cobordisms
between contact manifolds. Based on joint work with Kai Cieliebak and Peter
Albers.
Basak Gürel:
Title: From Lusternik-Schnirelmann theory to Conley conjecture
Abstract: In this talk I will discuss a recent result showing that whenever
a closed symplectic manifold admits a Hamiltonian diffeomorphism with
finitely many simple periodic orbits, the manifold has a spherical homology
class of degree two with positive symplectic area and positive integral of
the first Chern class. This theorem encompasses all known cases of the
Conley conjecture (symplectic CY and negative monotone manifolds) and also
some new ones (e.g., weakly exact symplectic manifolds with non-vanishing
first Chern class). The proof hinges on a general Lusternik–Schnirelmann
type result that, under some natural additional conditions, the sequence of
mean spectral invariants for the iterations of a Hamiltonian diffeomorphism
never stabilizes. Based on joint work with Viktor Ginzburg.