Subtle characteristic classes and Hermitian forms

Fabio Tanania

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arXiv · 1903.05579

Subtle characteristic classes and Hermitian forms

Fabio Tanania

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Abstract

Following [14], we compute the motivic cohomology ring of the Nisnevich classifying space of the unitary group associated to the standard split hermitian form of a quadratic extension. This provides us with subtle characteristic classes which take value in the motivic cohomology of the \v{C}ech simplicial scheme associated to a hermitian form. Comparing these new classes with subtle Stiefel-Whitney classes arising in the orthogonal case, we obtain relations among the latter ones holding in the motivic cohomology of the \v{C}ech simplicial scheme associated to a quadratic form divisible by a 1-fold Pfister form. Moreover, we present a description of the motive of the torsor corresponding to a hermitian form in terms of its subtle characteristic classes.

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BibTeX RIS

Fabio Tanania. 2019-03-13. Subtle characteristic classes and Hermitian forms. https://arxiv.org/abs/1903.05579

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