A note on local Floer homology

Abstract

In general, Lagrangian Floer homology - if well-defined - is not isomorphic to singular homology. For arbitrary closed Lagrangian submanifolds a local version of Floer homology is defined in [Flo89, Oh96] which is isomorphic to singular homology. This construction assumes that the involved Hamiltonian function $H$ is sufficiently $C^2$-small and the almost complex structure is sufficiently standard. In this note we develop a new construction of local Floer homology which works for any (compatible) almost complex structure and all Hamiltonian function with Hofer norm less than the minimal (symplectic) area of a holomorphic disk or sphere. The example $S^1\subset\C$ shows that this is sharp. If the Lagrangian submanifold is monotone, the grading of local Floer homology can be improved to a $\Z$-grading.