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arXiv · 1009.0354

On the Smoothness of Centralizers in Reductive Groups

Sebastian Herpel
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Abstract

Let G be a connected reductive algebraic group over an algebraically closed field k. In a recent paper, Bate, Martin, Röhrle and Tange show that every (smooth) subgroup of G is separable provided that the characteristic of k is very good for G. Here separability of a subgroup means that its scheme-theoretic centralizer in G is smooth. Serre suggested extending this result to arbitrary, possibly non-smooth, subgroup schemes of G. The aim of this note is to prove this more general result. Moreover, we provide a condition on the characteristic of k that is necessary and sufficient for the smoothness of all centralizers in G. We finally relate this condition to other standard hypotheses on connected reductive groups.

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Sebastian Herpel. 2011-12-16. On the Smoothness of Centralizers in Reductive Groups. https://arxiv.org/abs/1009.0354

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