Open enumerative mirror symmetry for lines in the mirror quintic

Abstract: Mirror symmetry gives predictions for the genus zero Gromov-Witten invariants of a closed Calabi--Yau variety in terms of period integrals on a mirror family of Calabi-Yau varieties. We deduce an analogous mirror theorem for the open Gromov-Witten invariants of certain Lagrangian submanifolds of the quintic threefold from homological mirror symmetry, assuming the existence of a negative cyclic open-closed map. The Lagrangians we consider can be thought of as SYZ mirrors to lines, and their open Gromov-Witten (OGW) invariants coincide with relative period integrals on the mirror quintic calculated by Walcher. Their OGW invariants are irrational numbers contained in an algebraic extension of the rationals, and admit an expression similar to the Ooguri-Vafa multiple cover formula involving special values of a Dirichlet L-function. We achieve these results by studying the Floer theory of a different immersed Lagrangian in the quintic that supports a one-dimensional family of objects in the Fukaya category homologically mirror to coherent sheaves supported on lines in the mirror quintic. The field in which the OGW invariants lie arises as the invariant trace field of (the smooth locus of) a closely related hyperbolic Lagrangian submanifold with conical singularities in the quintic. These results explain some of the predictions on the existence of hyperbolic Lagrangian submanifolds in the quintic put forward by Jockers-Morrison-Walcher.