## Seminars and Colloquia by Series

Monday, October 14, 2013 - 14:05 , Location: Skiles 006 , None , UNC Greensboro , Organizer: Dan Margalit
Monday, October 7, 2013 - 14:05 , Location: Skiles 006 , , University of Illinois at Chicago , , Organizer: Stavros Garoufalidis
In a paper published in 2012, Nathan Dunfield and StavrosGaroufalidis gave simple, sufficient conditions for a spunnormal surface tobe essential in a compact, orientable 3-manifold with torus boundary. Thistalk will discuss a generalization of this result which utilizes a theoremfrom tropical geometry.
Monday, September 30, 2013 - 14:00 , Location: Skiles 006 , Dheeraj Kulkarni , Georgia Tech , Organizer: John Etnyre
The $4$-genus of a knot is an important measure of complexity, related tothe unknotting number. A fundamental result used to study the $4$-genusand related invariants of homology classes is the Thom conjecture,proved by Kronheimer-Mrowka, and its symplectic extension due toOzsvath-Szabo, which say that closed symplectic surfacesminimize genus.Suppose (X, \omega) is a symplectic 4-manifold with contact type bounday and Sigma is a symplectic surface in X such that its boundary is a transverse knot in the boundary of X. In this talk we show that there is a closed symplectic 4-manifold Y with a closed symplectic submanifold S such that the pair (X, \Sigma) embeds symplectically into (Y, S).  This gives a proof of the relative version of Symplectic Thom Conjecture. We use this to study 4-genus of fibered knots in the 3-sphere.We will also discuss a relative version of Giroux's criterion of Stein fillability. This is joint work with Siddhartha Gadgil
Monday, September 23, 2013 - 15:05 , Location: Skiles 006 , Tara Brendle , U Glasgow , Organizer: Dan Margalit
The so-called integral Burau representation gives a symplectic representation of the braid group.  In this talk we will discuss the resulting congruence subgroups of braid groups, that is, preimages of the principal congruence subgroups of the symplectic group.  In particular, we will show that the level 4 congruence braid group is equal to the group generated by squares of Dehn twists.  One key tool is a "squared lantern relation" amongst Dehn twists. Joint work with Dan Margalit.
Monday, September 16, 2013 - 14:00 , Location: Skiles 006 , Lawrence Roberts , University of Alabama , Organizer: John Etnyre
Khovanov homology is an invariant of a link in S^3 which refines the Jones polynomial of the link. Recently I defined a version of Khovanov homology for tangles with interesting locality and gluing properties, currently called bordered Khovanov homology, which follows the algebraic pattern of bordered Floer homology. After reviewing the ideas behind bordered Khovanov homology, I will describe what appears to be the Jones polynomial-like structure which bordered Khovanov homology refines.
Monday, September 9, 2013 - 14:05 , Location: Skiles 006 , Igor Belegradek , Georgia Tech , Organizer: Igor Belegradek
It is known that any complete nonnegatively curved metric on the plane is conformally equivalent to the Euclidean metric. In the first half of the talk I shall explain that the conformal factors that show up correspond precisely to smooth subharmonic functions of minimal growth. The proof is function-theoretic. This characterization of conformal factors can be used to study connectedness properties of the space of complete nonnegatively curved metrics on the plane. A typical result is that the space of metrics cannot be separated by a finite dimensional subspace. The proofs use infinite-dimensional topology and dimension theory. This is a joint work with Jing Hu.
Wednesday, September 4, 2013 - 14:00 , Location: Skiles 006 , Youlin Li , Georgia Tech , Organizer: John Etnyre
We introduce the (homologically essential) arc complex of a surface as a tool for studying properties of open book decompositions and contact structures. After characterizing destabilizability in terms of the essential translation distance of the monodromy of an open book we given an application of this result to show that there are planer open books of the standard contact structure on the 3-sphere with 5 (or any number larger than 5) boundary components that do not destabilize. We also show that any planar open book with 4 or fewer boundary components does destabilize. This is joint work with John Etnyre.
Monday, September 2, 2013 - 14:32 , Location: Skiles 006 , None , None , Organizer: John Etnyre
Monday, August 26, 2013 - 14:00 , Location: Skiles 006 , John Etnyre , Georgia Tech , Organizer: John Etnyre
We will discuss how to define two invariants of knots using sutured Heegaard Floer homology, contact structures and limiting processes. These invariants turn out to be a reformulation of the plus and minus versions of knot Heegaard Floer homology and thus give asutured interpretation'' of these invariants and point to a deep connection between Heegaard Floer theory and contact geometry. If time permits we will also discuss the possibility of defining invariants of non-compact manifolds and of contact structures on such manifolds.
Monday, April 15, 2013 - 14:00 , Location: Skiles 006 , Peter Lambert-Cole , LSU , Organizer: John Etnyre
Legendrian contact homology is an invariant in contact geometry that assigns to each Legendrian submanifold a dg-algebra.  While well-defined, it depends upon counts of holomorphic curves that can be hard to calculate in practice.  In this talk, we introduce a class of Legendrian tori constructed as the product of collections of Legendrian knots.  For this class, we discuss how to explicitly compute the dg-algebra invariant of the tori in terms of diagram projections of the constituent Legendrian knots.