Thursday, 29 November 2007

ag.algebraic geometry - Algebraic versus Analytic Brauer Group

Let X be a smooth projective algebraic variety over mathbbC. Then I think that someone (Serre?) showed that the Cohomological Etale Brauer Group agrees with the torsion part of the Analytic Brauer Group H2(X,mathcalOtimes). This latter group is calculated in the classical (metric) topology on the associated complex manifold with the sheaf of nowhere vanishing holomorphic functions.



However there can easily be non-torsion elements in H2(X,mathcalOtimes): for instance consider the image in H3(X,mathbbZ)cap(H(2,1)(X)oplusH(1,2)(X)).



Could there be a topology more refined than etale but defined algebraically which can see these non-torsion classes? Notice that one can also ask the question for any Hi(X,mathcalOtimes). For i=0,1 the Zariski and etale work fine.



Why do things break down for i>1?

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