Willmore Legendrian surfaces in pseudoconformal 5-sphere

Abstract

Let $ X: M \hook S^5$ be a compact Legendrian surface in pseudoconformal(CR) 5-sphere. We introduce a pseudoconformally invariant Willmore type second order functional $ \W(X)$, and study its critical points called Willmore Legendrian surfaces. The fifth order structure equations show that Willmore dual can be defined for a class of Willmore Legendrian surfaces. Moreover when this dual is constant, Willmore Legendrian surface admits a Weierstra\ss type representation in terms of immersed meromorphic curve in $ \C^2$ satisfying an appropriate real period condition via pseudoconformal stereographic projection. We show that every compact Riemann surface admits a generally one to one, conformal, Willmore Legendrian immersion in $ S^5$ with constant Willmore dual. As a corollary, every compact Riemann surface can be conformally immersed in $ \C^2$ as an exact, algebraic Lagrangian surface.