Special Lagrangian submanifolds and Algebraic complexity one Torus Actions

Abstract

In the first part of this paper we consider compact algebraic manifolds M^2n with an algebraic (n-1)-Torus action. We show that there is a T-invariant meromorphic section $\sigma$ of the canonical bundle of M. Any such $\sigma$ defines a divisor D. On the complement M'=M-D we have a trivialization of the canonical bundle and a T-action. If the first cohomology of M' vanishes, then results of [2] imply that there is a Special Lagrangian (SLag) fibration on M'. We study how the fibers compactify in M and give examples of SLag fibrations on M', including some cases there the first cohomology of M' doesn't vanish. In the second part of the paper we study Calabi-Yau hypersurfaces in M. We assume that $\sigma$ is an inverse of a holomorphic section $\eta$ of the anti-canonical bundle of M. We will see that under certain assumptions one can choose a holomorphic volume form on the smooth part D' of the divisor D s.t. orbits of the T-action give a SLag fibration on D' with respect to the metric, induced from M. Transversal sections $\eta_j$ near $\eta$ define smooth Calabi-Yau hypersurfaces D_j in M. We will show that one can deform the SLag fibration on D' to SLag fibrations on large parts of D_j. This construction applies for instance for D_j being quintics in CP^4 or Calabi-Yau hypersurfaces in the Grassmanian G(2,4).