Deligne's purity and compatible-systems conjecture for lisse sheaves

Let pp and \ell be distinct primes. Let XX be a connected normal scheme of finite type over Fp\mathbb{F}_p, and let E\mathcal{E} be an irreducible lisse Q\overline{\mathbb{Q}}_\ell-sheaf whose determinant has finite order. For a closed point xx of XX, write Frobx\operatorname{Frob}_x for its Frobenius and choose a geometric point xˉ\bar{x} above it. Then E\mathcal{E} is pure of weight 00; there is a number field EQE\subset\overline{\mathbb{Q}}_\ell such that det(1Frobxt,Exˉ)\det(1-\operatorname{Frob}_xt,\mathcal{E}_{\bar{x}}) has coefficients in EE for every closed point xx; for every non-archimedean place λ\lambda of EE prime to pp, its roots are λ\lambda-adic units; and, for sufficiently large EE, there is for every such λ\lambda an EλE_\lambda-sheaf Eλ\mathcal{E}_\lambda compatible with E\mathcal{E}, meaning that

det(1Frobxt,Exˉ)=det(1Frobxt,Eλ,xˉ)\det(1-\operatorname{Frob}_xt,\mathcal{E}_{\bar{x}})=\det(1-\operatorname{Frob}_xt,\mathcal{E}_{\lambda,\bar{x}})

for every closed point xx. Deligne's conjecture. These four properties should hold simultaneously. The conjecture is proved for curves by L. Lafforgue; parts concerning purity, integrality, and coefficients are known in general, and the compatible-systems assertion is proved for smooth varieties, while the full normal-variety statement is not established here.

Sources & referencesView supporting material

Primary source

Koji Shimizu, “Existence of compatible systems of lisse sheaves on arithmetic schemes”, arXiv:1509.05941 (2016).

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