paper

Mixed Weil cohomologies

arXiv:0712.3291 · doi:10.1016/j.aim.2011.10.021

Abstract

We define, for a regular scheme and a given field of characteristic zero $\KK$, the notion of $\KK$-linear mixed Weil cohomology on smooth -schemes by a simple set of properties, mainly: Nisnevich descent, homotopy invariance, stability (which means that the cohomology of $\GG_{m}$ behaves correctly), and Künneth formula. We prove that any mixed Weil cohomology defined on smooth -schemes induces a symmetric monoidal realization of some suitable triangulated category of motives over to the derived category of the field $\KK$. This implies a finiteness theorem and a Poincaré duality theorem for such a cohomology with respect to smooth and projective -schemes (which can be extended to smooth -schemes when is the spectrum of a perfect field). This formalism also provides a convenient tool to understand the comparison of such cohomology theories. Our main examples are algebraic de Rham cohomology and rigid cohomology, and the Berthelot-Ogus isomorphism relating them.

update references; hopefully improve the exposition

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