Floer cohomology in the mirror of the projective plane and a binodal cubic curve

Abstract

We construct a family of Lagrangian submanifolds in the Landau–Ginzburg mirror to the projective plane equipped with a binodal cubic curve as anticanonical divisor. These objects correspond under mirror symmetry to the powers of the twisting sheaf $\mathcal{O}\left(1\right)$, and hence their Floer cohomology groups form an algebra isomorphic to the homogeneous coordinate ring. An interesting feature is the presence of a singular torus fibration on the mirror, of which the Lagrangians are sections. This gives rise to a distinguished basis of the Floer cohomology and the homogeneous coordinate ring parameterized by fractional integral points in the singular affine structure on the base of the torus fibration. The algebra structure on the Floer cohomology is computed using the symplectic techniques of Lefschetz fibrations and the topological quantum field theory counting sections of such fibrations. We also show that our results agree with the tropical analogue proposed by Abouzaid, Gross, and Siebert. Extensions to a restricted class of singular affine manifolds and to mirrors of the complements of components of the anticanonical divisor are discussed.