Displaceability in Symplectic Geometry
We use a topological condition by Albers that is sufficient for nondisplaceability to describe a large class of nondisplaceable Lagrangians, namely the anti-diagonals of closed monotone symplectic manifolds. We provide some examples of closed monotone symplectic manifolds of Euler characteristic zero. Furthermore, we study the displaceability of fibers of the bending flow system on equilateral pentagon space. Besides torus fibers over points in the interior of moment map image, this completely integrable system has two Lagrangian sphere fibers over boundary points of the moment polytope. They are nondisplaceable for topological reasons. Most of the regular torus fibers are displaceable using McDuff’s probes technique. We prove that the central torus fiber is nondisplaceable by showing that we can lift a Hamiltonian diffeomorphism displacing it to a Hamiltonian diffeomorphism displacing the central torus fiber of the Gelfand-Cetlin system on the complex Grassmannian of 2-planes. This fiber is known to be nondisplaceable.