R. Hazrat: Reduced K-theory of Azumaya Algebras

r.hazrat@qub.ac.uk

Submission: 2005, Sep 13

In the theory of central simple algebras, often we are dealing with abelian groups which arise from the kernel or co-kernel of functors which respect transfer maps (for example $K$-functors). Since a central simple algebra splits and the functors above are trivial'' in the split case, one can prove certain calculus on these functors. The common examples are kernel or co-kernel of the maps $K_i(F) \rightarrow K_i(D)$, where $K_i$ are Quillen $K$-groups, $D$ is a division algebra and $F$ its centre, or the homotopy fiber arising from the long exact sequence of above map, or the reduced Whitehead group $\SK$. In this note we introduce an abstract functor over the category of Azumaya algebras which covers all the functors mentioned above and prove the usual calculus for it. This, for example, immediately shows that $K$-theory of an Azumaya algebra over a local ring is almost'' the same as $K$-theory of the base ring. The main result is to prove that reduced $K$-theory of an Azumaya algebra over a Henselian ring coincides with reduced $K$-theory of its residue central simple algebra. The note ends with some calculation trying to determine the homotopy fibers mentioned above.

2000 Mathematics Subject Classification:

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