Deligne's conjecture on Frobenius invariants of lisse sheaves with fixed local monodromy

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Let CC be a smooth curve over a finite field Fq\mathbb F_q, let Cˉ\bar C be its smooth compactification, and let MM be the set of irreducible lisse Qˉℓ\bar{\mathbb Q}_\ell-sheaves of rank rr on C⊗FqFC\otimes_{\mathbb F_q}\mathbb F with prescribed local data. Define

2d=dim⁡H1(Cˉ⊗FqF,j∗End⁡(V)).2d=\dim H^1(\bar C\otimes_{\mathbb F_q}\mathbb F,j_*\operatorname{End}(V)).

Let N(n)N(n) denote the cardinality of the FnF^n-invariants of MM. Deligne's conjecture. (i) There are finitely many Weil numbers ai,bja_i,b_j of weights between 00 and 2d2d such that

N(n)=∑iain−∑jbjn.N(n)=\sum_i a_i^n-\sum_j b_j^n.

(ii) If M≠∅M\neq\emptyset, precisely one of the numbers ai,bja_i,b_j has weight 2d2d; it is one of the aia_i and equals qdq^d. The conjecture predicts a precise Weil-number description of the point counts of the moduli problem with fixed local monodromy. The supplied text gives the geometric setup and the asserted formula but no resolution status.

References

Primary source

Hélène Esnault and Moritz Kerz, “A finiteness theorem for Galois representations of function fields over finite fields (after Deligne)”, arXiv:1208.0128 (2012).

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