Deligne's companions conjecture for normal varieties

Let Fq\mathbb{F}_q be a finite field of characteristic pp, let X0X_0 be a connected normal variety over Fq\mathbb{F}_q, let p\ell\ne p be a prime, and let V0\mathcal{V}_0 be an irreducible Weil lisse Q\overline{\mathbb{Q}}_{\ell}-sheaf over X0X_0 with finite-order determinant. Let EE be the number field generated by the coefficients of the Frobenius polynomials of V0\mathcal{V}_0 at closed points. A Weil lisse EλE_{\lambda}-sheaf is EE-compatible with V0\mathcal{V}_0 when it has the same Frobenius polynomials under the embedding determined by the finite place λ\lambda. Companions conjecture. After possibly replacing EE with a finite extension, for every finite place λ\lambda not dividing pp there exists a Weil lisse EλE_{\lambda}-sheaf EE-compatible with V0\mathcal{V}_0. This conjecture extends the known companion results for smooth varieties to normal varieties; the paper studies the obstruction in the singular case and proves it for some singular normal varieties. The status of the conjecture in general is open.

Sources & referencesView supporting material

Primary source

Marco D'Addezio, “Some remarks on the companions conjecture for normal varieties”, arXiv:2006.09954 (2020).

Additional references

4 papers in this index state this conjecture (2017–2020). The statement above is taken from the most recent of them; the others are arXiv:1811.00204, arXiv:1809.02106, arXiv:1711.04797.

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