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Fano Pseudoindex


The Fano pseudoindex of a positive-dimensional Fano manifold is the least anticanonical degree of an irreducible rational curve,

 iota_X=min{-K_X·C:C subset X is an irreducible rational curve}.

Rational curves exist on a Fano manifold, so this minimum is defined. For projective space P^n with n>=1, it is n+1, realized by a line. For a product space of positive-dimensional projective spaces, it is one more than the smallest factor dimension.

The generalized Mukai conjecture relates the pseudoindex to dimension and Picard number. Its equality case has all factor dimensions equal to iota_X-1.


See also

Anticanonical Bundle, Fano Index, Fano Manifold, Generalized Mukai Conjecture, Picard Number, Rational Curve

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References

Bonavero, L.; Casagrande, C.; Debarre, O.; and Druel, S. "Sur une conjecture de Mukai." Comment. Math. Helv. 78, 601-626, 2003. https://doi.org/10.1007/S00014-003-0765-X.

Cite this as:

Weisstein, Eric W. "Fano Pseudoindex." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/FanoPseudoindex.html

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