Zak's conjecture on cohomological normality of projective varieties

Let XX be a non-degenerate projective mm-dimensional subvariety of Pn\mathbb{P}^n, and let ii and jj be integers with i1i\geq 1 and j0j\geq 0.

Zak's conjecture. 1.

Hi(Pn,IX(j))=0H^i(\mathbb{P}^n,\mathcal{I}_X(j))=0

whenever

i+j<mnm1.i+j<\frac{m}{n-m-1}.
  1. When
i+j=mnm1,i+j=\frac{m}{n-m-1},

it should be possible to classify all varieties for which

Hi(Pn,IX(j))0.H^i(\mathbb{P}^n,\mathcal{I}_X(j))\neq 0.

This conjecture generalizes the question of classifying non-degenerate projective varieties with exceptional failure of jj-normality. The source presents it as a conjecture of F. L. Zak; no resolution is given here.

Sources & referencesView supporting material

Primary source

Pietro De Poi and Emilia Mezzetti, “Congruences of lines in P^5, quadratic normality, and completely exceptional Monge-Ampère equations”, arXiv:0710.5110 (2007).

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