The algebra conjecture for parameterizing motivic local systems

Let YY be a smooth projective geometrically connected variety over the finite field Fq\mathbb F_q, let DD be an effective divisor on YY, and let NN be a positive integer. Let CFq\mathcal C_{\mathbb F_q} be the tensor category used in the source, and let ϕn\phi_n denote its numerical realization over Q\mathbb Q.

Algebra conjecture for motivic local systems. There exists a commutative associative unital algebra A=AY,D,NA=A_{Y,D,N} in CFq\mathcal C_{\mathbb F_q} such that, for every n1n\ge 1, ϕn(A)\phi_n(A) is semisimple over Q\mathbb Q, and for every prime ll with (l,q)=1(l,q)=1 there is a bijection

HomQ-alg(ϕn(A),Q)\operatorname{Hom}_{\mathbb Q\text{-alg}}(\phi_n(A),\overline{\mathbb Q})

with the elements of IrrRepY×FqFqn,Nmot,geom\operatorname{IrrRep}^{\mathrm{mot,geom}}_{Y\times_{\mathbb F_q}\mathbb F_{q^n},N} whose ramification divisor is DD. The bijection is equivariant for the natural action of Gal(Q/Q)×Z/nZ{\operatorname{Gal}}(\overline{\mathbb Q}/\mathbb Q)\times\mathbb Z/n\mathbb Z.

This conjecture proposes a finite-dimensional algebra whose geometric points parameterize motivic local systems with prescribed ramification. It would organize the expected independence from ll and the Galois and cyclic symmetries, but is not established in the source.

Sources & referencesView supporting material

Primary source

Maxim Kontsevich, “Notes on motives in finite characteristic”, arXiv:math/0702206 (2007).

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