A Terracini Lemma for osculating spaces with applications to Veronese surfaces

首个非空 Terracini 轨迹的几何

Geometry of first nonempty Terracini loci

本文刻画了 Veronese、Segre-Veronese 簇及 del Pezzo 曲面的非空 Terracini 轨迹，并提出一种显式计算给定簇 Terracini 轨迹的算法。

Osculating spaces to secant varieties

We generalize the classical Terracini's Lemma to higher order osculating spaces to secant varieties. As an application, we address with the so-called Horace method the case of the $d$-Veronese embedding of the projective 3-space.

On the infinitesimal Terracini lemma

In this paper we prove an infinitesimal version of the classical Terracini Lemma for 3--secant planes to a variety. Precisely we prove that if $X\subseteq \PP^r$ is an irreducible, non--degenerate, projective complex variety of dimension $n$ with $r\geq 3n+2$, such that the variety of osculating planes to curves in $X$ has the expected dimension $3n$ and for every $0$--dimensional, curvilinear scheme $γ$ of length 3 contained in $X$ the family of hyperplanes sections of $X$ which are singular along $γ$ has dimension larger that $r-3(n+1)$, then $X$ is $2$--secant defective.

On the Terracini locus of projective varieties

We introduce and study properties of the Terracini locus of projective varieties X, which is the locus of finite subsets S of X such that 2S fails to impose independent conditions to a linear system L. Terracini loci are relevant in the study of interpolation problems over double points in special position, but they also enter naturally in the study of special loci contained in secant varieties to projective varieties. We find some criteria which exclude that a set S belongs to the Terracini locus. Furthermore, in the case where X is a Veronese variety, we bound the dimension of the Terracini …

Osculating Varieties of Veronesean and their higher secant varieties

We consider the varieties $O_{k,n.d}$ of the k-osculating spaces to the Veronese varieties, the $d-$uple embeddings of $\PP n$; we study the dimension of their higher secant varieties. Via inverse systems (apolarity) and the study of certain spaces of forms we are able, in several cases, to determine whether those secant varieties are defective or not.

On varieties with higher osculating defect

In this paper, using the method of moving frames, we generalise some of Terracini's results on varieties with tangent defect. In particular, we characterise varieties with higher order osculating defect in terms of Jacobians of higher fundamental forms and moreover we characterise varieties with "small" higher fundamental forms as contained in scrolls.