Homaloidal hypersurfaces and hypersurfaces with vanishing Hessian

We introduce various families of irreducible homaloidal hypersurfaces in projective space Pr, for all r?3. Some of these are families of homaloidal hypersurfaces whose degrees are arbitrarily large as compared to the dimension of the ambient projective space. The existence of such a family solves a question that has naturally arisen from the consideration of the classes of homaloidal hypersurfaces known so far. The result relies on a fine analysis of hypersurfaces that are dual to certain scroll surfaces. We also introduce an infinite family of determinantal homaloidal hypersurfaces based on a certain degeneration of a generic Hankel matrix. The latter family fit non-classical versions of de Jonquières transformations. As a natural counterpoint, we broaden up aspects of the theory of Gordan-Noether hypersurfaces with vanishing Hessian determinant, bringing over some more precision into the present knowledge.     

Cohomogeneity one manifolds and hypersurfaces of the euclidean space

This paper is aimed at studying compact hypersurfaces of the euclidean space which are supposed to be Riemannian manifolds of cohomogeneity one, namely acted on by a Lie group of intrinsic isometries with principal orbits of codimension one. We give necessary and sufficient conditions on the structure of the Riemannian metric in order that a hypersurface of such kind turns out to be a revolution hypersurface.     

Strictly locally convex hypersurfaces with prescribed curvature and boundary in space forms

Abstract

This article is devoted to C² a priori estimates for strictly locally convex radial graphs with prescribed Weingarten curvature and boundary in space forms. By constructing two-step continuity process and applying degree theory arguments, existence results in space forms are established for prescribed Gauss curvature equation under the assumption of a strictly locally convex subsolution.     

Linear programs with an additional rank two reverse convex constraint

An efficient algorithm is developed for solving linear programs with an additional reverse convex constraint having a special structure. Computational results are presented and discussed.     

New minimal hypersurfaces in and

We find a class of minimal hypersurfaces as the zero level set of Pfaffians, resp. determinants of real dimensional antisymmetric matrices. While and are congruent to the quadratic cone resp. Hsiang's cubic invariant in , (special harmonic ‐invariant cones of degree ⩾4) seem to be new.     

Cubic hypersurfaces admitting an embedding with Gauss map of rank 0

We give a characterization of Fermat cubic hypersurfaces of dimension greater than 2 in characteristic 2 in terms of the property, called (GMRZ), that a projective variety admits an embedding whose Gauss map is of rank 0. In contrast to the higher dimensional case, for cubic surfaces the above characterization is no longer true. Moreover, we prove that the process of blowing up at points preserves the property (GMRZ), and that every smooth rational surface in fact satisfies (GMRZ) in the characteristic 2 case.     

K-duality for pseudomanifolds with an isolated singularity

We associate to a pseudomanifold X with an isolated singularity a differentiable groupoid G which plays the role of the tangent space of X. We construct a Dirac element D and a Dual Dirac element λ which induce a Poincaré duality in K-theory between the $\text{C}{}^1$-algebras C(X) and $\text{C}{}^1\text{(G)}$. To cite this article: C. Debord, J.-M. Lescure, C. R. Acad. Sci. Paris, Ser. I 336 (2003).     

A splitting criterion for an isolated singularity at x = 0 in a family of even hypersurfaces

Assume given a family of even local analytic hypersurfaces, whose central fiber has an isolated singularity at x =?0 which is not an ordinary double point. We prove that if the family is sufficiently general, for instance if the general fiber is smooth and the general singular fiber has only ordinary double points, then the singularity at x = 0 “splits in codimension one”, i.e., the local discriminant divisor has an irreducible component, over which a general fiber has more than one singularity specializing to the original one. As a corollary, we deduce the result by Grushevsky and Salvati Manni (Singularities of the theta divisor at points of order two, IMRN, 2007, Proposition 8) that on a principally polarized abelian variety (A, Θ) with dim(A) = g ≥ 4, a singularity of even multiplicity on Θ, isolated or not, at a point of order two and not an ordinary double point, must be a limit of two distinct ordinary double points {x, ?x} on nearby theta divisors.     

Functions Holomorphic along Holomorphic Vector Fields

The main result of the paper is the following generalization of Forelli’s theorem (Math. Scand. 41:358–364, 1977): Suppose F is a holomorphic vector field with singular point at p, such that F is linearizable at p and the matrix is diagonalizable with eigenvalues whose ratios are positive reals. Then any function φ that has an asymptotic Taylor expansion at p and is holomorphic along the complex integral curves of F is holomorphic in a neighborhood of p. We also present an example to show that the requirement for ratios of the eigenvalues to be positive reals is necessary. K.T. Kim and G. Schmalz were supported by the Scientific visits to Korea program of the AAS and KOSEF. E. Poletsky was supported by NSF Grant DMS-0500880. G. Schmalz gratefully acknowledges support and hospitality of the Max-Planck-Institut für Mathematik Bonn.     

Holomorphic continuation of functions from closed hypersurfaces with singular edges

Consider a bounded domain D in ℂ ⁿ such that its boundary contains a finite set of singular edges. We study the boundary behavior of the Bochner-Martinelli integral over such domains. As an application, we obtain generalizations of Hartogs-Bochner and Aizenberg-Kytmanov theorems on the holomorphic continuation of functions from the boundary into the domain.     

Real rank versus nonnegative rank

We consider the set of m×n nonnegative real matrices and define the nonnegative rank of a matrix A to be the minimum k such that A=BC where B is m×k and C is k×n. Given that the real rank of A is j for some j, we give bounds on the nonnegative rank of A and A².     

Anisotropic eigenvalues upper bounds for hypersurfaces in weighted Euclidean spaces

We prove anisotropic Reilly-type upper bounds for divergence-type operators on hypersurfaces of the Euclidean space in presence of a weighted measure.     

Inequalities between rank moments of overpartitions

F.G. Garvan proved an inequality between crank moments and rank moments of partitions which utilizes an inequality for symmetrized rank and crank moments. In this paper, we study two symmetrized rank moments of overpartitions and prove an inequality between two rank moments of overpartitions.     

On two upper bounds for hypersurfaces involving a Thas’ invariant

Let $X^n$ be a hypersurface in ${\mathbb{P}}^{n+1}$ with $n\ge 1$ defined over a finite field ${\mathbb{F}}_q$ of $q$ elements. In this note, we classify, up to projective equivalence, hypersurfaces $X^n$ as above which reach two elementary upper bounds for the number of ${\mathbb{F}}_q$-points on $X^n$ which involve a Thas’ invariant.