## Seminars and Colloquia by Series

Monday, August 29, 2016 - 14:00 , Location: Skiles 006 , Weiwei Wu , University of Georgia , Organizer: John Etnyre

In this talk we first introduce a new "singularity-free" approach&nbsp;to the proof of Seidel's long exact sequence, including the fixed-point&nbsp;version. This conveniently generalizes to Dehn twists along Lagrangian&nbsp;submanifolds which are rank one symmetric spaces and their covers,&nbsp;including RPn and CPn, matching a mirror prediction due to Huybrechts and&nbsp;Thomas. The idea of the proof can be interpreted as a "mirror" of the&nbsp;construction in algebraic geometry, realized by a new surgery and cobordism&nbsp;construction. &nbsp;This is a joint work with Cheuk-Yu Mak.

Monday, August 22, 2016 - 14:05 , Location: Skiles 006 , Rebecca Winarski , University of Wisconsin at Milwaukee , Organizer: Dan Margalit
Birman and Hilden ask: given finite branched cover X over the 2-sphere, does every homeomorphism of the sphere lift to a homeomorphism of X?  For covers of degree 2, the answer is yes, but the answer is sometimes yes and sometimes no for higher degree covers.  In joint work with Ghaswala, we completely answer the question for cyclic branched covers.  When the answer is yes, there is an embedding of the mapping class group of the sphere into a finite quotient of the mapping class group of X.  In a family where the answer is no, we find a presentation for the group of isotopy classes of homeomorphisms of the sphere that do lift, which is a finite index subgroup of the mapping class group of the sphere.  Our family introduces new examples of orbifold Picard groups of subloci of Teichmuller space that are finitely generated but not cyclic.
Thursday, June 23, 2016 - 14:00 , Location: Skiles 005 , Yajing Liu , UCLA , Organizer: John Etnyre
Existence of tight contact structures is a fundamental question of contact topology. Etnyre and Honda first gave the example which doesn't admit any tight structure. The existence of fillable tight structures is also a subtle question. Here we give some new examples of hyperbolic 3-manifolds which do not admit any fillable structures.
Monday, June 6, 2016 - 14:05 , Location: Skiles 114 , , University of Maryland , , Organizer: Stavros Garoufalidis
We discuss the higher Teichmuller space A_{G,S} defined by Fockand Goncharov. This space is defined for a punctured surface S withnegative Euler characteristic, and a semisimple, simply connected Lie groupG. There is a birational atlas on A_{G,S} with a chart for each idealtriangulation of S. Fock and Goncharov showed that the transition functionsare positive, i.e. subtraction-free rational functions. We will show thatwhen G has rank 2, the transition functions are given by explicit quivermutations.
Tuesday, May 31, 2016 - 14:00 , Location: Skiles 006 , Caitlin Leverson , Duke University , Organizer: John Etnyre
Given a plane field $dz-xdy$ in $\mathbb{R}^3$. A Legendrian knot is a knot which at every point is tangent to the plane at that point. One can similarly define a Legendrian knot in any contact 3-manifold (manifold with a plane field satisfying some conditions). In this talk, we will explore Legendrian knots in $\mathbb{R}^3$, $J^1(S^1)$, and $\#^k(S^1\times S^2)$ as well as a few Legendrian knot invariants. We will also look at the relationships between a few of these knot invariants. No knowledge of Legendrian knots will be assumed though some knowledge of basic knot theory would be useful.
Monday, May 16, 2016 - 14:00 , Location: Skiles 006 , Jennifer Hom , Georgia Tech , Organizer: John Etnyre
Auckly gave two examples of irreducible integer homology spheres (one toroidal and one hyperbolic) which are not surgery on a knot in the three-sphere. Using an obstruction coming from Heegaard Floer homology, we will provide infinitely many hyperbolic examples, as well as infinitely many examples with arbitrary JSJ decomposition. This is joint work with Lidman.
Monday, April 25, 2016 - 14:00 , Location: Skiles 006 , Nicholas J. Kuhn , University of Virginia , Organizer: Kirsten Wickelgren
In a 1958 paper, Milnor observed that then new work by Bott allowed him to show that the n sphere admits a  vector bundle with non-trivial top Stiefel-Whitney class precisely when n=1,2,4, 8.  This can be interpreted  as a calculation of the mod 2 Hurewicz map for the classifying space BO, which has the structure of an  infinite loopspace. I have been studying Hurewicz maps for infinite loopspaces by showing how a filtration of the homotopy  groups coming from stable homotopy theory (the Adams filtration) interacts with a filtration of the homology groups coming from infinite loopspace theory. There are some clean and tidy consequences that lead to a new proof of Milnor's theorem, and other applications.
Tuesday, April 19, 2016 - 13:00 , Location: Skiles 006 , David Gay , University of Georgia , Organizer: John Etnyre

Please note different day and time for the seminar

In honor of John Stallings' great paper, "How not to prove the Poincare conjecture", I will show how to reduce the smooth 4-dimensional Poincare conjecture to a (presumably incredibly difficult) statement in group theory. This is joint work with Aaron Abrams and Rob Kirby. We use trisections where Stallings used Heegaard splittings.
Monday, April 11, 2016 - 14:00 , Location: Skiles 006 , Jonathan Beardsley , Johns Hopkins University , Organizer: Kirsten Wickelgren
Given an action by a loop space on a structured ring spectrum we describe how to produce its associated quotient ring spectrum.  We then describe how this structure may be leveraged to produce intermediate Hopf-Galois extensions of ring spectra, analogous to the way one produces intermediate Galois extensions from normal subgroups of a Galois group. We will give many examples of this structure in classical cobordism spectra and in particular describe an entirely new construction of the complex cobordism spectrum which bears a striking resemblance to Lazard's original construction of the Lazard ring by iterated extensions.
Friday, April 1, 2016 - 14:05 , Location: Skiles 006 , William Menasco , U Buffalo , Organizer: Dan Margalit
In Watchareepan Atiponrat's thesis the properties of decomposable exact Lagrangian codordisms betweenLegendrian links in R^3 with the standard contact structure were studied.  In particular, for any decomposableexact Lagrangian filling L of a Legendrian link K, one may obtain a normal ruling of K associated with L.Atiponrat's main result is that the associated normal rulings must have an even number of clasps.  As a result, there exists a Legendrian (4,-(2n +5))-torus knot, for each n >= 0, which does not have a decomposable exact Lagrangian filling because it has only 1 normal ruling and this normal rolling has odd number of clasps.