Equiaffine geometry of level sets and ruled hypersurfaces with equiaffine mean curvature zero

Basic aspects of the equiaffine geometry of level sets are developed systematically. As an application there are constructed families of 2n‐dimensional nondegenerate hypersurfaces ruled by n‐planes, having equiaffine mean curvature zero, and solving the affine normal flow. Each carries a symplectic structure with respect to which the ruling is Lagrangian.     

Blaschke Dupin hypersurfaces and equiaffine tubes

We give constructions of Blaschke Dupin hypersurfaces and a Blaschke isoparametric ones in terms of the notion of an equiaffine tube. In particular, the construction of Blaschke isoparametric hypersurfaces includes the Calabi-type composition of improper affine spheres (or an improper one and a proper one).     

Canonical equiaffine hypersurfaces in ℝ n+1

Supported by Technische Universit?t Berlin     

The quadratic slice theorem and the equiaffine tube theorem for equiaffine Dupin hypersurfaces

The main purpose of this paper is to investigate the quadraticity of slices (i.e., leaves of curvature foliations) of a non-degenerate equiaffine Dupin hypersurface, where an equiaffine Dupin hypersurface is the notion defined as the equiaffine geometrical version of a (not necessarily complete) Dupin hypersurface.     

On Cartan’s identities of equiaffine isoparametric hypersurfaces

The purpose of the present paper is to obtain Gartan’s identities for affine principal curvatures of an equiaffine isoparametric hypersurface under certain conditions. The result can be applied to a pseudo-Riemannian isoparametric hypersurface and a Blaschke isoparametric hypersurface.     

Deformations of Calabi-Yau hypersurfaces arising from deformations of toric varieties

One can deform the complex structure of Calabi-Yau hypersurfaces in toric varieties by changing the coefficients of the defining polynomial. However, there must also exist non-polynomial deformations of the Calabi-Yau hypersurfaces which cannot be realized inside the ambient toric variety. In this paper, we have constructed the missing non-polynomial deformations, which are induced by an automorphism on the open part of the ambient toric variety. Mathematics Subject Classification (1991) 14M25     

Internal geometry of hypersurfaces in projectively metric space

In this paper, we study the internal geometry of a hypersurface V _n−1 embedded in a projectively metric space K _n , n ≥ 3, and equipped with fields of geometric-objects { G_nⁱ,G_i } \left\{ {G_n^i,{G_i}} \right\} and { H_nⁱ,G_i } \left\{ {H_n^i,{G_i}} \right\} in the sense of Norden and with a field of a geometric object { H_nⁱ,H_n } \left\{ {H_n^i,{H_n}} \right\} in the sense of Cartan. For example, we have proved that the projective-connection space P _n−1,n−1 induced by the equipment of the hypersurface V_{n - 1}   ì   K_n,  n 3 3 {V_{n - 1}}\; \subset \;{K_n},\;n \geq 3 , in the sense of Cartan with the field of a geometrical object { H_nⁱ,H_n } \left\{ {H_n^i,{H_n}} \right\} is flat if and only if its normalization by the field of the object { H_nⁱ,G_i } \left\{ {H_n^i,{G_i}} \right\} in the tangent bundle induces a Riemannian space R _n−1 of constant curvature K = −1/c.     

Birational geometry of Fano hypersurfaces of index two

Mathematische Annalen - We prove that every non-trivial structure of a rationally connected fibre space on a generic (in the sense of Zariski topology) hypersurface V of degree M in the $$(M+1)$$...     

Conformal structure in affine geometry: Complete tchebychev hypersurfaces

We give a conformal classification of affine-complete centroaffine Tchebychev hypersurfaces recently introduced by Liu and Wang. This classification is based on partial differential equations known from conformal Riemannian geometry. Moreover we investigate Tchebychev hyperovaloids and generalize the classical theorem of Blaschke and Deicke on affine hyperspheres.     

Noncharacteristic hypersurfaces for complexes of differential operators

Sunto Sia X una varietà differenziabile ed S una ipersuperficie orientata in X. Si consideri un complesso di operatori differenziali su X. Se S è formalmente non caratteristica, esso induce un complesso di operatori su S. Si generalizza la nozione di simbolo di un operatore differensiale al caso di multigradazioni e si dimostra che, se S è non caratteristica, modulo «trasformazioni fibra» il complesso indotto è un complesso di operatori differenziali. In particolare, se una ipersuperficie è non caratteristica rispetto alla nozione usuale di simbolo, il complesso al bordo è sempre un complesso di operatori differenziali. Nell'ultima parte del lavoro si studio, il complesso al bordo indotto dal complesso di Hilbert dell'operatore .     

Pseudo-minkowski differential geometry

Summary Minkowski geometry is studied by the method of moving frames. In memory of Guido Castelnuovo, in the recurrence of the first centenary of his birth. The support of the research presented in these lectures by the Air Force Office of Scientific Research is gratefully acknowledged.