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Holomorphic maps onto varieties of non-negative Kodaira dimension. (English) Zbl 1112.14014

Summary: A classical result in complex geometry says that the automorphism group of a manifold of general type is discrete. It is more generally true that there are only finitely many surjective morphisms between two fixed projective manifolds of general type. Rigidity of surjective morphisms, and the failure of a morphism to be rigid have been studied by a numher of authors in the past. The main result of this paper states that surjective morphisms are always rigid, unless there is a clear geometric reason for it. More precisely, we can say the following. First, deformations of surjective morphisms between normal projective varieties are unobstructed unless the target variety is covered by rational curves. Second, if the target is not covered hy rational curves, then surjective morphisms are infinitesimally rigid, unless the morphism factors via a variety with positive-dimensional automorphism group. In this case, the Hom-scheme can be completely described.

MSC:

14E07 Birational automorphisms, Cremona group and generalizations
14A10 Varieties and morphisms
14J50 Automorphisms of surfaces and higher-dimensional varieties
14J40 \(n\)-folds (\(n>4\))
14E05 Rational and birational maps
32H02 Holomorphic mappings, (holomorphic) embeddings and related questions in several complex variables
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