Deligne's companions conjecture for normal varieties

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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 ℓ≠p\ell\ne p be a prime, and let V0\mathcal{V}_0 be an irreducible Weil lisse Q‾ℓ\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.

References

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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