Seminars and Colloquia by Series

Berge duals and universally tight contact structures

Series
Geometry Topology Seminar
Time
Monday, April 2, 2012 - 14:00 for 1 hour (actually 50 minutes)
Location
Skiles 005
Speaker
Chris CornwellDuke University
Berge has a construction that produces knots in S^3 that admit a lens space surgery. Conjecturally, his construction produces all such knots. This talk will consider knots that have such a surgery, and some of their contact geometric properties. In particular, knots in S^3 with a lens space surgery are fibered, and they all support the tight contact structure on S^3. From recent work of Hedden and Plamenevskaya, we also know that the dual to a lens space surgery on such a knot supports a tight contact structure on the resulting lens space. We consider the knots that are dual to Berge's knots, and we investigate whether the tight contact structure they support is a universally tight structure. Our results indicate a relationship between supporting this universally tight structure and being dual to a torus knot.

Curve complex translation lengths

Series
Geometry Topology Seminar
Time
Monday, March 26, 2012 - 14:05 for 1 hour (actually 50 minutes)
Location
Skiles 005
Speaker
Vaibhav GadreHarvard University
The curve complex C(S) of a closed orientable surface S of genusg is an infinite graph with vertices isotopy classes of essential simpleclosed curves on S with two vertices adjacent by an edge if the curves canbe isotoped to be disjoint. By a celebrated theorem of Masur-Minsky, thecurve complex is Gromov hyperbolic. Moreover, a pseudo-Anosov map f of Sacts on C(S) as a hyperbolic isometry with "north-south" dynamics and aninvariant quasi-axis. One can define an asymptotic translation length for fon C(S). In joint work with Chia-yen Tsai, we prove bounds on the minimalpseudo-Anosov asymptotic translation lengths on C(S) . We shall alsooutline related interesting results and questions.

Asymptotic Geometry of Teichmuller Space and Divergence

Series
Geometry Topology Seminar
Time
Monday, March 12, 2012 - 14:05 for 1 hour (actually 50 minutes)
Location
Skiles 006
Speaker
Harold SultanColumbia University
I will talk about the asymptotic geometry of Teichmuller space equipped with the Weil-Petersson metric. In particular, I will give a criterion for determining when two points in the asymptotic cone of Teichmuller space can be separated by a point; motivated by a similar characterization in mapping class groups by Behrstock-Kleiner-Minsky-Mosher and in right angled Artin groups by Behrstock-Charney. As a corollary, I will explain a new way to uniquely characterize the Teichmuller space of the genus two once punctured surface amongst all Teichmuller space in that it has a divergence function which is superquadratic yet subexponential.

On triangulating a square

Series
Geometry Topology Seminar
Time
Monday, February 27, 2012 - 14:05 for 1 hour (actually 50 minutes)
Location
Skiles 006
Speaker
Aaron AbramsEmory University
I will discuss the following geometric problem. If you are given an abstract 2-dimensional simplicial complex that is homeomorphic to a disk, and you want to (piecewise linearly) embed the complex in the plane so that the boundary is a geometric square, then what are the possibilities for the areas of the triangles? It turns out that for any such simplicial complex there is a polynomial relation that must be satisfied by the areas. I will report on joint work with Jamie Pommersheim in which we attempt to understand various features of this polynomial, such as the degree. One thing we do not know, for instance, if this degree is expressible in terms of other known integer invariants of the simplicial complex (or of the underlying planar graph).

The quantum content of the Neumann-Zagier equations

Series
Geometry Topology Seminar
Time
Monday, February 20, 2012 - 14:05 for 1 hour (actually 50 minutes)
Location
Skiles 005
Speaker
Stavros GaroufalidisGeorgia Tech
The Neumann-Zagier equations are well-understood objects of classical hyperbolic geometry. Our discovery is that they have a nontrivial quantum content, (that for instance captures the perturbation theory of the Kashaev invariant to all orders) expressed via universal combinatorial formulas. Joint work with Tudor Dimofte.

Fully irreducible outer automorphisms of the outer automorphism group of a free group

Series
Geometry Topology Seminar
Time
Friday, February 17, 2012 - 14:00 for 1 hour (actually 50 minutes)
Location
Skiles 006
Speaker
Alexandra PettetUniversity of British Columbia
The outer automorphism group Out(F) of a non-abelian free group F of finite rank shares many properties with linear groups and the mapping class group Mod(S) of a surface, although the techniques for studying Out(F) are often quite different from the latter two. Motivated by analogy, I will present some results about Out(F) previously well-known for the mapping class group, and highlight some of the features in the proofs which distinguish it from Mod(S).

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