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Varieties of minimal rational tangents on uniruled projective manifolds. (English) Zbl 0978.53118
Schneider, Michael (ed.) et al., Several complex variables. Cambridge: Cambridge University Press. Math. Sci. Res. Inst. Publ. 37, 351-389 (1999).
Summary: On a polarized uniruled projective manifold we pick an irreducible component $${\mathcal K}$$ of the Chow space whose generic members are free rational curves of minimal degree. The normalized Chow space of minimal rational curves marked at a generic point is nonsingular, and its strict transform under the tangent map gives a variety of minimal rational tangents, or VMRT. In this survey we present a systematic study of VMRT by means of techniques from differential geometry (distributions, $$G$$-structures), projective geometry (the Gauss map, tangency theorems), the deformation theory of (rational) curves, and complex analysis (Hartogs phenomenon, analytic continuation).
We give applications to a variety of problems on uniruled projective manifolds, especially on irreducible Hermitian symmetric manifolds $$S$$ of the compact type and more generally on rational homogeneous manifolds $$G/P$$ of Picard number 1, including the deformation rigidity of $$S$$ and the same for homogeneous contact manifolds of Picard number 1, the characterization of $$S$$ of rank at least 2 among projective uniruled manifolds in terms of $$G$$-structures, solution of Lazarsfeld’s Problem for finite holomorphic maps from $$G/P$$ of Picard number 1 onto projective manifolds, local rigidity of finite holomorphic maps from a fixed projective manifold onto $$G/P$$ of Picard number 1 other than $$\mathbb{P}^n$$, and a proof of the stability of tangent bundles of certain Fano manifolds.
For the entire collection see [Zbl 0933.00014].

##### MSC:
 53C55 Global differential geometry of Hermitian and Kählerian manifolds 14J45 Fano varieties 53C30 Differential geometry of homogeneous manifolds 53C10 $$G$$-structures 53C12 Foliations (differential geometric aspects) 32G05 Deformations of complex structures
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