Singular Levi-flat hypersurfaces in complex projective space induced by curves in the Grassmannian

Let H ⊂ ℙn be a real-analytic subvariety of codimension one induced by a real-analytic curve in the Grassmannian G(n + 1, n). Assuming H has a global defining function, we prove H is Levi-flat, the closure of its smooth points of top dimension is a union of complex hyperplanes, and its singular set is either of dimension 2n - 2 or dimension 2n - 4. If the singular set is of dimension 2n - 4, then we show the hypersurface is algebraic and the Levi-foliation extends to a singular holomorphic foliation of ℙn with a meromorphic (rational of degree 1) first integral. In this case, H is in some sense simply a complex cone over an algebraic curve in ℙ1. Similarly if H has a degenerate singularity, then H is also algebraic. If the dimension of the singular set is 2n - 2 and is nondegenerate, we show by construction that the hypersurface need not be algebraic nor semialgebraic. We construct a Levi-flat real-analytic subvariety in ℙ2 of real codimension 1 with compact leaves that is not contained in any proper real-algebraic subvariety of ℙ2. Therefore a straightforward analogue of Chow's theorem for Levi-flat hypersurfaces does not hold.

Remark on Zero Sets of Holomorphic Functions in Convex Domains of Finite Type

We prove that if the (1, 1)-current of integration on an analytic subvariety V ⊂ D satisfies the uniform Blaschke condition, then V is the zero set of a holomorphic function ƒ such that log |ƒ| is a function of bounded mean oscillation in bD. The domain D is assumed to be smoothly bounded and of finite d’Angelo type. The proof amounts to non-isotropic estimates for a solution to the -equation for Carleson measures.

A Big Picard Theorem for Holomorphic Maps into Complex Projective Space

We prove a big Picard type extension theoremfor holomorphic maps f : X–A → M, where X is a complex manifold, A is an analytic subvariety of X, and M is the complement of the union of a set of hyperplanes in ℙn but is not necessarily hyperbolically imbedded in ℙn.

Holomorphic automorphisms and cancellation theorems

Let X be a complex analytic space of positive dimension and A a complex analytic subvariety of X. We call A a direct factor of X if there exist a complex analytic space B and a biholomorphic mapping f: A × B → X such that, for some b ∊ B, f(a, b) = a on A, and a complex analytic space X to be primary if X has no direct factor, not equal to X itself, of positive dimension.

An Application of Logic to Analysis

Let F be a complex analytic subvariety of an open subset of Cn and p ϵ V let be the germs at p of holomorphic, weakly holomorphic, infinitely differentiable, and k times continuously differentiate functions respectively. Spallek [15] has shown that for any p £ V there exists an integer such that , generalizing the result of Malgrange [12] that .In [14], Siu proved Spallek's result from a more sheaf theoretic point of view and showed the minimal integer function is bounded on compact sets. Bloom [7] reproved Malgrange's result by using differential operators on varieties.

Holomorphic extension of continuous, weakly holomorphic functions on certain analytic varieties

Let M, N be connected complex submanifolds of a neighborhood of the origin 0 ∈ Cd, the space of d complex variables, such that 0 ∈ M ∩ N. We shall suppose throughout that M ⊄ N and N ⊄ M in any neighborhood of 0. Let X = M ∪ N. X is an analytic subvariety with the irreducible branches M and N. Let Δ be a neighborhood of 0 in Cd.