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Chow-Witt rings of classifying spaces for symplectic and special linear groups. (English) Zbl 1444.14018
Summary: We compute the Chow-Witt rings of the classifying spaces for the symplectic and special linear groups. In the structural description we give, contributions from real and complex realization are clearly visible. In particular, the computation of cohomology with $$\mathbf{I}^j$$-coefficients is done closely along the lines of Brown’s computation of integral cohomology for special orthogonal groups. The computations for the symplectic groups show that Chow-Witt groups are a symplectically oriented ring cohomology theory. Using our computations for special linear groups, we also discuss the question when an oriented vector bundle of odd-rank splits off a trivial summand.

MSC:
 14C17 Intersection theory, characteristic classes, intersection multiplicities in algebraic geometry 19G12 Witt groups of rings 19D45 Higher symbols, Milnor $$K$$-theory 55R40 Homology of classifying spaces and characteristic classes in algebraic topology
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