Lagrangian Intersection Floer Homology
The Lagrangian Floer homology of two Lagrangian submanifolds of a symplectic manifold is the homology of a chain complex which is generated by the intersection points of the two submanifolds and whose differential counts pseudoholomorphic Whitney discs. The symplectic Floer homology of a symplectomorphism of M can be thought of as the special case of Lagrangian Floer homology in which the ambient manifold is M cross M and the Lagrangian submanifolds are the diagonal and the graph of the symplectomorphism. The construction of Heegaard Floer homology (see above) is based on a variant of Lagrangian Floer homology. The theory also appears in work of Seidel–Smith and Manolescu exhibiting what is conjectured to be part of the combinatorially-defined Khovanov homology as a Lagrangian intersection Floer homology.
Given three Lagrangian submanifolds L0, L1, and L2 of a symplectic manifold, there is a product structure on the Lagrangian Floer homology:
which is defined by counting holomorphic triangles (that is, holomorphic maps of a triangle whose vertices and edges map to the appropriate intersection points and Lagrangian submanifolds).
Papers on this subject are due to Fukaya, Oh, Ono, and Ohta; the recent work on "cluster homology" of Lalonde and Cornea offer a different approach to it. The Floer homology of a pair of Lagrangian submanifolds may not always exist; when it does, it provides an obstruction to isotoping one Lagrangian away from the other using a Hamiltonian isotopy.
Read more about this topic: Floer Homology
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