Subvarieties of generic complete intersections. II (original) (raw)

1991, Mathematische Annalen

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This paper investigates the Hilbert scheme of a generic complete intersection in a Grassmann variety, specifically examining the properties of smooth projective subvarieties within this context. The authors demonstrate that under certain conditions, every smooth projective subvariety is of general type, thereby generalizing earlier results related to curves on hypersurfaces. Additionally, the study explores the implications of Koszul resolutions and discusses potential connections to existing conjectures in the field.

On the canonical degrees of curves in varieties of general type

Geometric and Functional Analysis, 2012

In this paper, we work in the framework of complex analytic varieties; without contrary mention, varieties are assumed to be irreducible (and reduced). If C is a projective curve, we let g C be its geometric genus (namely, the genus of its desingularization) and χ(C) = 2 − 2g C its geometric Euler characteristic; we also write deg C L for the degree of a line bundle L on C.

On the genus and Hartshorne-Rao module of projective curves

Mathematische Zeitschrift, 1998

In this paper optimal upper bounds for the genus and the dimension of the graded components of the Hartshorne-Rao module of curves in projective n-space are established. This generalizes earlier work by Hartshorne [H] and Martin-Deschamps and Perrin [MDP]. Special emphasis is put on curves in P 4 . The first main result is a so-called Restriction Theorem. It says that a non-degenerate curve of degree d ≥ 4 in P 4 over a field of characteristic zero has a non-degenerate general hyperplane section if and only if it does not contain a planar curve of degree d−1 (see Th. 1.3). Then, using methods of Brodmann and Nagel, bounds for the genus and Hartshorne-Rao module of curves in P n with non-degenerate general hyperplane section are derived. It is shown that these bounds are best possible in a very strict sense. Coupling these bounds with the Restriction Theorem gives the second main result for curves in P 4 . Then curves of maximal genus are investigated. The Betti numbers of their minimal free resolutions are computed and a description of all reduced curves of maximal genus in P n of degree ≥ n + 2 is given. Finally, all pairs (d, g) of integers which really occur as the degree d and genus g of a non-degenerate curve in P 4 are described.

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