Kac's conjecture for coherent sheaves on weighted projective lines

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Let Xp,λ‾\mathbb{X}_{\mathbf{p},\underline{\lambda}} be a weighted projective line, let Lg\mathfrak{Lg} be its corresponding loop Kac–Moody algebra, and use the identification K0(Coh⁡(Xp,λ‾))≃hLg∗K_0(\operatorname{Coh}(\mathbb{X}_{\mathbf{p},\underline{\lambda}}))\simeq\mathfrak{h}^*_{\mathfrak{Lg}}. For a coherent sheaf F\mathcal{F}, write [F][\mathcal{F}] for its class. Kac's conjecture for weighted projective lines. The following hold: (i) there exists an indecomposable coherent sheaf F∈Coh⁡(Xp,λ‾)\mathcal{F}\in\operatorname{Coh}(\mathbb{X}_{\mathbf{p},\underline{\lambda}}) if and only if [F]∈hLg∗[\mathcal{F}]\in\mathfrak{h}^*_{\mathfrak{Lg}} is a positive root; moreover, the set of such indecomposables forms a 1−(α,α)21-\frac{(\alpha,\alpha)}{2}-parameter family with a unique component of maximal dimension; (ii) for every root α\alpha there exists a polynomial Pα(v)∈N[v]P_\alpha(v)\in\mathbb{N}[v] with leading term v1−(α,α)2v^{1-\frac{(\alpha,\alpha)}{2}} such that the number of absolutely indecomposable coherent sheaves of dimension α\alpha over Fq\mathbb{F}_q is Pα(q)P_\alpha(q), and Pα(0)=dim⁡LgαP_\alpha(0)=\operatorname{dim}\mathfrak{Lg}_\alpha. The supplied text presents this as a variant of Kac's quiver conjectures, but gives no resolution status.

References

Primary source

Olivier Schiffmann, “Noncommutative projective curves and quantum loop algebras”, arXiv:math/0205267 (2003).

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