Seminars and Colloquia by Series

Abelian cycles in the homology of the Torelli group

Series
Geometry Topology Seminar
Time
Monday, February 14, 2022 - 14:00 for 1 hour (actually 50 minutes)
Location
Online
Speaker
Erik LindellUniversity of Stockholm

The mapping class group of a compact and orientable surface of genus g has an important subgroup called the Torelli group, which is the kernel of the action on the homology of the surface. In this talk we will discuss the stable rational homology of the Torelli group of a surface with a boundary component, about which very little is known in general. These homology groups are representations of the arithmetic group Sp_{2g}(Z) and we study them using an Sp_{2g}(Z)-equivariant map induced on homology by the so-called Johnson homomorphism. The image of this map is a finite dimensional and algebraic representation of Sp_{2g}(Z). By considering a type of homology classes called abelian cycles, which are easy to write down for Torelli groups and for which we can derive an explicit formula for the map in question, we may use classical representation theory of symplectic groups to describe a large part of the image.

Stable commutator length on big mapping class groups

Series
Geometry Topology Seminar
Time
Monday, February 7, 2022 - 14:00 for 1 hour (actually 50 minutes)
Location
Speaker
Elizabeth FieldUniversity of Utah

The stable commutator length function measures the growth rate of the commutator length of powers of elements in the commutator subgroup of a group. In this talk, we will discuss the stable commutator length function on the mapping class groups of infinite-type surfaces which satisfy a certain topological characterization. In particular, we will show that stable commutator length is a continuous function on these big mapping class groups, as well as that the commutator subgroups of these big mapping class groups are both open and closed. Along the way to proving our main results, we will discuss certain topological properties of a class of infinite-type surfaces and their end spaces which may be of independent interest. This talk represents joint work with Priyam Patel and Alexander Rasmussen.

Stein property of complex-hyperbolic Kleinian groups

Series
Geometry Topology Seminar
Time
Monday, January 31, 2022 - 14:00 for 1 hour (actually 50 minutes)
Location
Online
Speaker
Subhadip DeyYale university

Let M be a complex-hyperbolic n-manifold, i.e. a quotient of the complex-hyperbolic n-space $\mathbb{H}^n_\mathbb{C}$ by a torsion-free discrete group of isometries, $\Gamma = \pi_1(M)$. Suppose that M is  convex-cocompact, i.e. the convex core of M is a nonempty compact subset. In this talk, we will discuss a sufficient condition on $\Gamma$ in terms of the growth-rate of its orbits in $\mathbb{H}^n_\mathbb{C}$ for which M is a Stein manifold. We will also talk about some interesting questions related to this result. This is a joint work with Misha Kapovich.

https://bluejeans.com/196544719/9518

The diffeomorphism group of a 4-manifold

Series
Geometry Topology Seminar
Time
Monday, January 24, 2022 - 14:00 for
Location
Online (Zoom)
Speaker
Danny RubermanBrandeis University

Associated to a smooth n-dimensional manifold are two infinite-dimensional groups: the group of homeomorphisms Homeo(M), and the group of diffeomorphisms, Diff(M). For manifolds of dimension greater than 4, the topology of these groups has been intensively studied since the 1950s. For instance, Milnor’s discovery of exotic 7-spheres immediately shows that there are distinct path components of the diffeomorphism group of the 6-sphere that are connected in its homeomorphism group.  The lowest dimension for such classical phenomena is 5. 

I will discuss recent joint work with Dave Auckly about these groups in dimension 4. For each n, we construct a simply connected 4-manifold Z and an infinite subgroup of the nth homotopy group of Diff(Z) that lies in the kernel of the natural map to the corresponding homotopy group of Homeo(Z). These elements are detected by (n+1)—parameter gauge theory. The construction uses a topological technique.  I’ll mention some other applications to embeddings of surfaces and 3-manifolds in 4-manifolds.
 

Zoom Link- https://brandeis.zoom.us/j/99772088777   (password- hyperbolic)

Here is alternative link where the password is embedded- https://brandeis.zoom.us/j/99772088777?pwd=WHpFQk1Fem5jZVRNRUwzVmpmck4xdz09 

Applications of contact geometry to 3-dimensional Anosov dynamics

Series
Geometry Topology Seminar
Time
Monday, November 29, 2021 - 14:00 for 1 hour (actually 50 minutes)
Location
Online (also Skiles 006)
Speaker
Federico SalmoiraghiTechnion

Meeting link: https://bluejeans.com/722836372/4781?src=join_info

Anosov flows are an important class of dynamical systems due to their ergodic properties and structural stability. Geometrically, they are defined by two transverse invariant foliations with expanding and contracting behaviors. Much of our understanding of the structure of an Anosov flow relies on the study of the leaves space of the invariant foliations. In this talk we adopt a different approach: in the early 90s Mitsumatsu first noticed that and Anosov vector field also belongs to the intersection of two transverse contact structures rotating towards each other. After giving the necessary background I will use this point of view to address questions in surgery theory on Anosov flows and contact structures.

Detection results in link Floer homology

Series
Geometry Topology Seminar
Time
Monday, November 15, 2021 - 14:00 for 1 hour (actually 50 minutes)
Location
Skiles 006
Speaker
Subhankar DeyUniverity of Alabama

In this talk I will briefly describe link Floer homology toolbox and its usefulness. Then I will show how link Floer homology can detect links with small ranks, using a rank bound for fibered links by generalizing an existing result for knots. I will also show that stronger detection results can be obtained as the knot Floer homology can be shown to detect T(2,8) and T(2,10), and that link Floer homology detects (2,2n)-cables of trefoil and figure eight knot. This talk is based on a joint work with Fraser Binns (Boston College).

A Fox-Milnor Condition for 1-Solvable Links

Series
Geometry Topology Seminar
Time
Monday, November 8, 2021 - 14:00 for 1 hour (actually 50 minutes)
Location
Skiles 006
Speaker
Shawn WilliamsRice University

A well known result of Fox and Milnor states that the Alexander polynomial of slice knots factors as f(t)f(t^{-1}), providing us with a useful obstruction to a knot being slice. In 1978 Kawauchi demonstrated this condition for the multivariable Alexander polynomial of slice links.  In this talk, we will present an extension of this result for the multivariable Alexander polynomial of 1-solvable links. (Note: This talk will be in person) 

Classical and new plumbings bounding contractible manifolds and homology balls

Series
Geometry Topology Seminar
Time
Monday, November 1, 2021 - 14:00 for 1 hour (actually 50 minutes)
Location
Online
Speaker
Oğuz ŞavkBoğaziçi University

A central problem in low-dimensional topology asks which homology 3-spheres bound contractible 4-manifolds and homology 4-balls. In this talk, we address this problem for plumbed 3-manifolds and we present the classical and new results together. Our approach is based on Mazur’s famous argument and its generalization which provides a unification of all results.

On amphichirality of symmetric unions (Virtual)

Series
Geometry Topology Seminar
Time
Monday, October 18, 2021 - 14:00 for 1 hour (actually 50 minutes)
Location
Skiles 006
Speaker
Ceren KoseThe University of Texas at Austin

Symmetric unions are an interesting class of knots. Although they have not been studied much for their own sake, they frequently appear in the literature. One such instance regards the question of whether there is a nontrivial knot with trivial Jones polynomial. In my talk, I will describe a class of symmetric unions, constructed by Tanaka, such that if any are amphichiral, they would have trivial Jones polynomial. Then I will show how such a knot not only answers the above question but also gives rise to a counterexample to the Cosmetic Surgery Conjecture. However, I will prove that such a knot is in fact trivial and hence cannot be used to answer any of these questions. Finally, I will discuss how the arguments that go into this proof can be generalized to study amphichiral symmetric unions.

Invariants of rational homology 3-spheres from the abelianization of the mod-p Torelli group (Virtual)

Series
Geometry Topology Seminar
Time
Monday, October 4, 2021 - 14:00 for 1 hour (actually 50 minutes)
Location
Speaker
Ricard Riba GarciaUAB Barcelona

Unlike the integral case, given a prime number p, not all Z/p-homology 3-spheres can be constructed as a Heegaard splitting with a gluing map an element of mod p Torelli group, M[p]. Nevertheless, letting p vary we can get any rational homology 3-sphere. This motivated us to study invariants of rational homology 3-spheres that comes from M[p]. In this talk we present an algebraic tool to construct invariants of rational homology 3-spheres from a family of 2-cocycles on M[p]. Then we apply this tool to give all possible invariants that are induced by a lift to M[p] of a family of 2-cocycles on the abelianization of M[p], getting a family of invariants that we will describe precisely.
 

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