The cone-of-curves formulation of the negative-curve conjecture

Let YY be the blow-up of P2\mathbb{P}^2 at a set of rr points in very general position. Write

NE(Y)=B1B2\partial \overline{\operatorname{NE}}(Y)=\mathcal{B}_1\sqcup\mathcal{B}_2

as in the source, where B1\mathcal{B}_1 is the closure of the union of the facets of the boundary of the effective cone and B2\mathcal{B}_2 is supported by Nul(Y)\operatorname{Nul}(Y). Let KY0K_Y^{\leq 0} and KY>0K_Y^{>0} denote the corresponding half-spaces, and let Pos(Y)\operatorname{Pos}(Y) and Nul(Y)\operatorname{Nul}(Y) be the positive cone and its boundary.

Cone-of-curves formulation. The extremal rays of B1\mathcal{B}_1 that do not lie on Nul(Y)\operatorname{Nul}(Y) are spanned by classes of (1)(-1)-curves, and

B1=NE(Y)KY0,B2=NE(Y)KY>0.\mathcal{B}_1=\partial\overline{\operatorname{NE}}(Y)\cap K_Y^{\leq 0},\qquad \mathcal{B}_2=\partial\overline{\operatorname{NE}}(Y)\cap K_Y^{>0}.

In particular,

NE(Y)KY0=Pos(Y)KY0.\overline{\operatorname{NE}}(Y)\cap K_Y^{\geq 0}=\operatorname{Pos}(Y)\cap K_Y^{\geq 0}.

This is presented as a more precise formulation of the negative-curve conjecture and describes the boundary of the effective cone for very general blow-ups of P2\mathbb{P}^2. The source does not give evidence that this formulation has been solved.

Sources & referencesView supporting material

Primary source

Tommaso de Fernex, “Negative curves on very general blow-ups of P^2”, arXiv:math/0512631 (2005).

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