Compact special Legendrian surfaces in $S^5$

TL;DR

This paper introduces a method for constructing compact special Legendrian surfaces in the 5-sphere, demonstrating the existence of high-genus Hamiltonian stationary Lagrangian surfaces in complex projective space, with potential smoothness and minimality.

Contribution

It develops a general approach to build compact special Legendrian surfaces of high genus via area minimization and reflection techniques, extending the understanding of such surfaces in complex geometry.

Findings

Existence of genus $1+rac{k(k-3)}{2}$ Hamiltonian stationary Lagrangian surfaces in $ ext{CP}^2$ for $k \\geq 3$.

Construction of smooth, branched, or singular Lagrangian surfaces through minimization and reflection.

Identification of conditions under which these surfaces are minimal and Legendrian.

Abstract

A surface $\Sigma \subset S^5 \subset \mathbb{C}^3$ is called \emph{special Legendrian} if the cone $0 \times \Sigma \subset \mathbb{C}^3$ is special Lagrangian. The purpose of this paper is to propose a general method toward constructing compact special Legendrian surfaces of high genus. It is proved \emph{there exists a compact, orientable, Hamiltonian stationary Lagrangian surface of genus $1+\frac{k(k-3)}{2}$ in $ \mathbb{C}P^2$ for each integer $ k \geq 3$, which is a smooth branched surface except at most finitely many conical singularities.} If this surface is smooth, it is minimal and the Legendrian lift of the surface is the desired compact special Legendrian surface. We first establish the existence of a minimizer of area among Lagrangian disks in a relative homotopy class of a K\"ahler-Einstein surface without Lagrangian homotopy classes with respect to a configuration $ \Gamma$ that consists of the fixed point loci of K\"ahler involutions. $ \Gamma$ in addition must satisfy certain null relative homotopy conditions and angle criteria. The fundamental domain thus obtained is smooth along the boundary, and has finitely many interior singular points. We then apply successive \emph{reflection} of this fundamental domain along its boundary to obtain a complete or compact Lagrangian surface.