Géométrie symplectique et espaces de modules
Org:
Thomas John Baird (Memorial),
Lisa Claire Jeffrey (Toronto) et
Steven Rayan (Saskatchewan)
[
PDF]
 TOM BAIRD, Memorial University
Harmonic forms on the ChenTeo gravitational instanton [PDF]

The famous nohair theorem in general relativity asserts that Kerr blackholes are the only nontrivial, stationary, axisymmetric, asymptotically flat solutions to the vacuum Einstein equations. A Riemannian/Euclidean version the nohair theorem was conjectured in the 70s. Namely, that the Euclidean Kerr metrics are the only nontrivial asymptotically flat gravitational instantons admitting a 2torus symmetry.
A surprising counterexample to this conjecture was discovered in 2011 by Chen and Teo. First constructed using the inverse scatter method, the metric has recently been proven to be conformal to a Kaehler metric on a toric variety (thus fitting with the theme of this session). In this talk I will survey some of these recent developments and discuss my work with Kunduri classifying L2harmonic forms on the ChenTeo gravitational instanton.
 PETER CROOKS, Northeastern University
Symplectic reduction and sheets [PDF]

Let $\mathfrak{g}$ be a finitedimensional semisimple Lie algebra over $\mathbb{C}$. Given a nonnegative integer $k$, one may consider the locus $\mathfrak{g}_k\subset\mathfrak{g}$ of elements with centralizer dimension equal to $k$. A locally closed subvariety of $\mathfrak{g}$ is called a sheet if it is an irreducible component of $\mathfrak{g}_k$ for some nonnegative integer $k$. These subvarieties are ubiquitous in Lietheoretic Poisson geometry.
I will give an overview of sheets and their incarnations in Poisson geometry and representation theory. This will lead to a description of ongoing work with Maxence Mayrand, in which we consider symplectic reduction along a sheet.
 SHENGDA HU, Wilfrid Laurier University
Degree of a generalized holomorphic bundle [PDF]

We discuss a notion of degree for a generalized holomorphic vector bundle over a generalized Kahler manifold, using generalized connections that are analogues of Chern connections in the classical situation. The resulting degree fits well with the analogue of HermitianYangMills equation, as proposed by Hitchin in 2011, in this context. Some general consequences of our constructions will be discussed as well.
 YUCONG JIANG, University of Toronto
Dirac structures in generalized Kähler geometry [PDF]

Abstract: Generalized Kähler (GK) structures were discovered by Gates, Hull, and Roček in 1984 during their study of N=(2,2) supersymmetric nonlinear sigma models and later on put into the framework of generalized complex geometry by Gualtieri in his 2003 thesis. In this talk, We will first review the construction of holomorphic Dirac structures in GK geometry and explain how they can be used to study the real and holomorphic Poisson structures occurring in a GK manifold. We will use tools from the theory of Lie groupoids, and see how symplectic groupoids, presymplectic groupoids and Poisson groupoids enter naturally in GK geometry and what they will imply for the underlying GK structure. Based on joint work Marco Gualtieri.
 RUXANDRA MORARU, University of Waterloo
CoHiggs bundles on Poisson surfaces [PDF]

CoHiggs bundles on a complex manifold $M$ are given by pairs $(E,\phi)$ consisting of a holomorphic vector bundle $E$ on $M$ together with a Higgs field $\phi \in H^0(M,\text{End}(E) \otimes TM)$ that satisfies certain integrability conditions. In particular, coHiggs bundles correspond to generalized holomorphic bundles on complex manifolds. They also give rise to a special class of holomorphic Poisson structures on the projective bundles $\mathbb{P}(E)$. CoHiggs bundles were first studied by S. Rayan on Riemann surfaces and $\mathbb{CP}^2$ in his thesis, where he also gave a nonexistence theorem for stable, traceless rank2 coHiggs bundles on K3 and generaltype surfaces. In this talk, we consider coHiggs bundles on all compact holomorphic Poisson surfaces. We give necessary and sufficient conditions for the existence of stable, traceless rank2 coHiggs bundles on all compact holomorphic Poisson surfaces as well as a complete classification of such bundles on some surfaces.
 DOUG PARK, University of Waterloo
Geography problem for simply connected symplectic 4manifolds [PDF]

We will discuss the following geography problem:
Given a pair of integers $(a,b)$, is there a simply connected minimal symplectic $4$dimensional manifold $M$ such that the Euler characteristic of $M$ is $a$, and the signature of $M$ is $b$?
Here, we say that a symplectic $4$dimensional manifold is minimal if it is not diffeomorphic to a symplectic blowup of some other symplectic $4$dimensional manifold.
If we restrict our attention to nonspin $4$dimensional manifolds, then this problem has been completely solved in the case when the signature variable $b$ is negative. We will discuss the remaining case when $b$ is nonnegative, highlighting the speaker's recent joint works with his collaborators.
 SHIYU SHEN, University of Toronto
Complex Ktheory of the moduli space of Higgs bundles [PDF]

The moduli spaces of semistable $\text{SL}_n$ and $\text{PGL}_n$ Higgs bundles form dual abelian fibrations over (generic locus of) an affine space called the Hitchin base. Motivated by the HauselThaddeus mirror symmetry picture, we construct an isomorphism between the complex Ktheory of the two moduli spaces on the spectra level. As part of our proof, we show both Ktheory groups are torsionfree. This is joint work in progress with Michael Groechenig.
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