Infinite CW-complexes, Brauer groups and phantom cohomology

Abstract

Expanding a result of Serre on finite CW-complexes, we show that the Brauer group coincides with the cohomological Brauer group for arbitrary compact spaces. Using results from the homotopy theory of classifying spaces for Lie groups, we give another proof of the result of Antieau and Williams that equality does not hold for Eilenberg--MacLane spaces of type K(Z/nZ,2). Employing a result of Dwyer and Zabrodsky, we show the same for the classifying spaces BG where G is an infinite-dimensional F_p-vector space. In this context, we also give a formula expressing phantom cohomology in terms of homology.