# Difference between revisions of "Symplectic Geometry Seminar"

Wednesday 3:30pm-4:30pm VV B139

date speaker title host(s)
Sept. 21st Ruifang Song The Picard-Fuchs equations of Calabi-Yau hypersurfaces in partial flag varieties
Sept. 28st Ruifang Song The Picard-Fuchs equations of Calabi-Yau hypersurfaces in partial flag varieties(continued)
Oct. 5th Dongning Wang Seidel Representation for Symplectic Orbifolds

## Abstracts

Ruifang Song The Picard-Fuchs equations of Calabi-Yau hypersurfaces in partial flag varieties

Abstract

We introduce a system of differential equations associated to a smooth algebraic variety X acted by a complex Lie group G and a G-linearlized line bundle L on X. We show that this system is holonomic and thus has finite dimensional solution space assuming G acts on X with finitely many orbits. When X is a partial flag variety, we show that this system gives the Picard-Fuchs system of Calabi-Yau hypersurfaces in X. In particular, when X is a toric variety, our construction recovers GKZ systems and extended GKZ systems, which have played important roles in studying periods of Calabi-Yau hypersurfaces/complete intersections in toric varieties. In general, if X is a Fano variety, L is the anticanonical line bundle and G=Aut(X), this construction can be used to study the Picard-Fuchs system of Calabi-Yau hypersurfaces/complete intersections in X.

Dongning Wang Seidel Representation for Symplectic Orbifolds

Abstract

For a symplectic manifold $\displaystyle{ (M,\omega) }$, Seidel representation is a group morphism from $\displaystyle{ \pi_1(Ham(M,\omega)) }$ to the multiplication group of the quantum cohomology ring $\displaystyle{ QH^*(M,\omega) }$. With this morphism, once given enough information about $\displaystyle{ \pi_1(Ham(M,\omega)) }$, one can get compute $\displaystyle{ QH^*(M,\omega) }$. On the other side, one would like to compute quantum cohomology of symplectic orbifolds defined by Chen and Ruan for many reasons, for example, to verify mirror symmetry between orbifolds and its mirror. With this motivation, we generalize Seidel representation to the orbifold cases. To do that, we need to generalize all the terminologies used to construct Seidel representation. For a symplectic orbifold $\displaystyle{ (\mathcal{X},\omega) }$, we define loops of Hamiltonian diffeomorphisms, $\displaystyle{ \pi_1(Ham(\mathcal{X},\omega)) }$, Hamiltonian orbifiber bundles, and sectional pseudoholomorphic orbicurves into the bundle. In this talk, I will explain these definitions and use them to construct Seidel representation for orbifolds.