Expected classification of even-dimensional quadratic forms of height two

Let ϕ\phi be an anisotropic quadratic form of even dimension over a field of characteristic not equal to 22, with height h(ϕ)=2h(\phi)=2. Let deg(ϕ)=d\deg(\phi)=d. A Pfister form is denoted by π\pi, and an excellent form is one similar to πσ\pi\otimes\sigma', where π\pi is a dd-fold Pfister form and σ\sigma' is the pure part of an (nd)(n-d)-fold Pfister form.

Expected height-two classification. Exactly one of the following holds:

  1. ϕπψ\phi\simeq\pi\otimes\psi for some (d1)(d-1)-fold Pfister form π\pi and 44-dimensional form ψ\psi of nontrivial discriminant.
  2. ϕπψ\phi\simeq\pi\otimes\psi for some (d2)(d-2)-fold Pfister form π\pi and 66-dimensional form ψ\psi of trivial discriminant.
  3. ϕ\phi is an excellent form of dimension 2n+12d2^{n+1}-2^d for some n>dn>d.

The statement is presented as the expected classification in the characteristic-not- equal-to-22 theory, in a discussion explicitly describing the problem as open.

Sources & referencesView supporting material

Primary source

Stephen Scully, “Hoffmann's conjecture for totally singular forms of prime degree”, arXiv:1410.8785 (2014).

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