We study singular real-analytic Levi-flat hypersurfaces in complex projective space. We give necessary and sufficient conditions for such a hypersurface to be a pullback of a real-analytic curve in C via a meromorphic function. We define the rank of a real hypersurface and study the connections between rank, degree, and the type and size of the singularity for Levi-flat hypersurfaces. Finally, ...

LetX be a compact, strictly convex C-hypersurface in the (n+1)-dimensional Euclidean space R. The Gauss map ofX maps the hypersurface one-to-one and onto the unit n-sphere S. One may parametrize X by the inverse of the Gauss map. Consequently, the Gauss curvature can be regarded as a function on S. The classical Minkowski problem asks conversely when a positive function K on S is the Gauss curv...

Let Nn+p p be an (n + p)-dimensional connected semi-Riemannian manifold of index p. It is called a semi-definite space of index p. When we refer to index p, we mean that there are only p negative eigenvalues of semi-Riemannian metric of Nn+p p and the other eigenvalues are positive. In particular, Nn+1 1 is called a Lorentz space when p = 1. When the Lorentz space Nn+1 1 is of constant curvatur...

Let M be an orientable connected and compact real hypersurface of the complex space form C(n+1)/2. If the mean curvature α and the function f = g(Aξ, ξ) of hypersurface M satisfy the inequalityn2α2 ≤ (n2 − 1)δ + f 2, where ξ is the characteristic vector field,A is the shape operator and (n− 1)δ is the infimum of the Ricci curvatures of hypersurface M , then it is shown that α is a constant and ...

In this article, we consider hypersurfaces moving with normal velocity depending on the timespace coordinates and on the normal to the hypersurface. We naturally define a measure associated to this hypersurface. This measure is defined on a suitable space/unit normal/curvature configuration space. We show that, while the hypersurface stays smooth, then the measure is a solution to a linear tran...

we study umbilic (space-like) submanifolds of pseudo-riemannian space forms, then define totally semi-umbilic space-like submanifold of pseudo euclidean space and relate this notion to umbilicity. finally we give characterization of total semi-umbilicity for space-like submanifolds contained in pseudo sphere or pseudo hyperbolic space or the light cone.a pseudo-riemannian submanifold m in (a ps...

We study the topology of the space ∂K of complete convex hypersurfaces of R which are homeomorphic to Rn−1. In particular, using Minkowski sums, we construct a deformation retraction of ∂K onto the Grassmannian space of hyperplanes. So every hypersurface in ∂K may be flattened in a canonical way. Further, the total curvature of each hypersurface evolves continuously and monotonically under this...

We show that the Hodge and pole order filtrations are different for a sufficiently general singular projective hypersurface of degree 3 or 4 if the dimension of the projective space is at least 5 or 3 respectively. We then prove a variant of Wotzlaw’s formula for the Hodge filtration in case the singular points of a hypersurface are ordinary double points and their images by the e-fold Veronese...

In this paper, we prove new pinching theorems for the first eigenvalue λ1(M) of the Laplacian on compact hypersurfaces of the Euclidean space. These pinching results are associated with the upper bound for λ1(M) in terms of higher order mean curvatures Hk. We show that under a suitable pinching condition, the hypersurface is diffeomorpic and almost isometric to a standard sphere. Moreover, as a...