The converse to Karpenko's theorem on ruled quadrics

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Let qq be an anisotropic quadratic form over a field kk. Its first Witt index is the Witt index of qq over the function field of its associated projective quadric. Converse to Karpenko's theorem. If the first Witt index of qq is greater than 11, then the associated projective quadric is ruled over kk. Karpenko's theorem states that anisotropic quadratic forms with first Witt index equal to 11 have non-ruled associated projective quadrics. The converse is conjectured in any characteristic; the source notes that it is proved there for quasilinear forms of every dimension.

References

Primary source

Burt Totaro, “Birational geometry of quadrics in characteristic 2”, arXiv:math/0608098 (2006).

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