The converse to Karpenko's theorem on ruled quadrics
The converse to Karpenko's theorem on ruled quadrics
Let be an anisotropic quadratic form over a field . Its first Witt index is the Witt index of over the function field of its associated projective quadric. Converse to Karpenko's theorem. If the first Witt index of is greater than , then the associated projective quadric is ruled over . Karpenko's theorem states that anisotropic quadratic forms with first Witt index equal to 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.
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Primary source
Burt Totaro, “Birational geometry of quadrics in characteristic 2”, arXiv:math/0608098 (2006).
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