Seminars and Colloquia by Series

Monday, November 7, 2016 - 14:00 , Location: Skiles 006 , Stefan Mueller , Georgia Southern University. , Organizer: John Etnyre
 We show that an embedding of a (small) ball into a contact manifold is contact if and only if it preserves the (modified) shape invariant. The latter is, in brief, the set of all cohomology classes that can be represented by the pull-back (to a closed one-form) of a contact form by a coisotropic embedding of a fixed manifold (of maximal dimension) and of a given homotopy type. The proof is based on displacement information about (non)-Lagrangian submanifolds that comes from J-holomorphic curve methods (and gives topological invariants), and the construction of a coisotropic torus whose image (under a given embedding that is not contact) admits a transverse contact vector field (i.e. a convex surface in dimension 3). The definition of shape preserving does not involve derivatives and is preserved by uniform convergence (on compact subsets). As a consequence, we prove C^0-rigidity of contact embeddings (and diffeomorphisms). The underlying ideas are adaptations of symplectic techniques to contact manifolds that, in contrast to symplectic capacities, work well in the contact setting; the heart of the proof however uses purely contact topological methods.
Monday, October 31, 2016 - 14:00 , Location: Skiles 006 , Juanita Pinzon-Caicedo , University of Georgia , Organizer: John Etnyre
Trisections of 4-manifolds relative to their boundary were introduced by Gay and Kirby in 2012. They are decompositions of 4-manifolds that induce open book decomposition in the bounding 3-manifolds. This talk will focus on diagrams of relative trisections and will be divided in two. In the first half I will focus on trisections as fillings of open book decompositions and I will present different fillings of different open book decompositions of the Poincare homology sphere. In the second half I will show examples of trisections of pieces of some of the surgery techniques that result in exotic 4-manifolds.
Monday, October 24, 2016 - 14:00 , Location: Skiles 006 , Bulent Tosun , University of Alabama , Organizer: John Etnyre
A Stein manifold is a complex manifold with particularly nice convexity properties. In real dimensions above 4, existence of a Stein structure is essentially a homotopical question, but for 4-manifolds the situation is more subtle.  An important question that has been circulating among contact and symplectic topologist for some time asks: whether every contractible smooth 4-manifold admits a Stein structure? In this talk we will provide examples that answer this question negatively. Moreover, along the way we will provide new evidence to a closely related conjecture of Gompf,  which asserts that a nontrivial Brieskorn homology sphere, with either orientation, cannot be embedded in complex 2-space as the boundary of a Stein submanifold.
Monday, October 17, 2016 - 14:05 , Location: Skiles 006 , Balazs Strenner , Georgia Institute of Technology , Organizer: Dan Margalit
Monday, October 10, 2016 - 14:00 , Location: None , None , None , Organizer: John Etnyre
Monday, October 3, 2016 - 14:05 , Location: Skiles 006 , Alper Gur , Indiana University , , Organizer: Mohammad Ghomi
The compact transverse cross-sections of a cylinder over a central ovaloid in Rn, n ≥ 3, with hyperplanes are central ovaloids. A similar result holds for quadrics (level sets of quadratic polynomials in Rn, n ≥ 3). Their compact transverse cross-sections with hyperplanes are ellipsoids, which are central ovaloids. In R3, Blaschke, Brunn, and Olovjanischnikoff found results for compact convex surfaces that motivated B. Solomon to prove that these two kinds of examples provide the only complete, connected, smooth surfaces in R3, whose ovaloid cross sections are central. We generalize that result to all higher dimensions, proving: If M^(n-1), n >= 4, is a complete, connected smooth hypersurface of R^n, which intersects at least one hyperplane transversally along an ovaloid, and every such ovaloid on M is central, then M is either a cylinder over a central ovaloid or a quadric.
Monday, September 26, 2016 - 14:00 , Location: Skiles 006 , Burak Ozbagci , UCLA and Koc University , Organizer: John Etnyre
We prove that any minimal weak symplectic filling of the canonical contact structure on the unit cotangent bundle of a nonorientable closed surface other than the real projective plane is s-cobordant rel boundary to the disk cotangent bundle of the surface. If the nonorientable surface is the Klein bottle, then we show that the minimal weak symplectic filling is unique up to homeomorphism. (This is a joint work with Youlin Li.)
Monday, September 19, 2016 - 14:00 , Location: Skiles 006 , Craig Westerland , University of Minnesota , Organizer: Kirsten Wickelgren
I will describe new techniques for computing the homology of braid groups with coefficients in certain exponential coefficient systems.  An unexpected side of this story (at least to me) is a connection with the cohomology of certain braided Hopf algebras — quantum shuffle algebras and Nichols algebras — which are central to the classification of pointed Hopf algebras and quantum groups. We can apply these tools to get a bound on the growth of the cohomology of Hurwitz moduli spaces of branched covers of the plane in certain cases.  This yields a weak form of Malle’s conjecture on the distribution of fields with prescribed Galois group in the function field setting.  This is joint work with Jordan Ellenberg and TriThang Tran.
Monday, September 12, 2016 - 14:00 , Location: Skiles 006 , Mark Lowell , University of Massachusetts , Organizer: John Etnyre
We consider two knot diagrams to be equivalent if they are isotopic without Reidemeister moves, and prove a method for determining if the equivalence class of a knot diagram contains a representative that is the Lagrangian projection of a Legendrian knot.   This work gives us a new tool for determining if a Legendrian knot can be de-stabilized.
Monday, September 5, 2016 - 14:00 , Location: None , None , None , Organizer: John Etnyre