Conjecture on the classification of varieties with full ramification locus

Let XX be a smooth complex variety of dimension n2n\ge 2. Let LL be an ample line bundle on XX, spanned by a subspace VH0(L)V\subseteq H^0(L) with dim(V)n+1\dim(|V|)\ge n+1. Let R(X,V)\mathcal{R}(X,V) denote the ramification locus associated with the linear system VV. Classification conjecture. If

R(X,V)=X,\mathcal{R}(X,V)=X,

then (X,L)(X,L) is one of (P2,OP2(2))(\mathbb{P}^{2},\mathcal{O}_{\mathbb{P}^{2}}(2)), (P1×P1,OP1×P1(1,1))(\mathbb{P}^{1}\times\mathbb{P}^{1},\mathcal{O}_{\mathbb{P}^{1}\times\mathbb{P}^{1}}(1,1)), or a scroll over a smooth curve. The examples preceding the conjecture motivate this proposed classification of ample spanned line bundles whose ramification locus is the whole variety; the statement is presented as a conjecture, and no resolution is supplied in the source.

Sources & referencesView supporting material

Primary source

Gian Mario Besana, Sandra Di Rocco and Antonio Lanteri, “Peculiar Loci of Ample and Spanned Line Bundles”, arXiv:math/0306139 (2003).

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