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Geometric Manin’s conjecture and rational curves. (English) Zbl 1451.14089

The article proves several interesting results about family of rational curves on a Fano variety. These have certain expected dimension and it is interesting to know whether it is the real dimension, and often it is not, what can be said about the ‘bad’ components and what are they. To state one of the theorems, one needs to define the Fujita invariant \(a(X,L)\) for a projective variety \(X\) and a \(\mathbb{Q}\)-Cartier nef divisor \(L\). This is the minimum real number \(t\) such that \(tL+K_X\) is in the cone of pseudo-effective divisors. Then the theorem says that the union of all \(Y\subset X\) (\(X\) Fano with \(L=-K_X\)) with \(a(Y,L_{|Y})>a(X,L)\) is a proper closed subvariety and the rational curves of a fixed degree with respect to \(L\) and not contained in this closed subvariety has the expected dimension.

MSC:

14H10 Families, moduli of curves (algebraic)
14M22 Rationally connected varieties

References:

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