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arXiv · 2207.03369

Non-Abelian extensions of groupoids and their groupoid rings

Natã Machado·Johan Öinert·Stefan Wagner
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Abstract

We present a geometrically oriented classification theory for non-Abelian extensions of groupoids generalizing the classification theory for Abelian extensions of groupoids by Westman as well as the familiar classification theory for non-Abelian extensions of groups by Schreier and Eilenberg-MacLane. As an application of our techniques we demonstrate that each extension of groupoids $\mathcal{N} \to \mathcal{E} \to \mathcal{G}$ gives rise to a groupoid crossed product of $\mathcal{G}$ by the groupoid ring of $\mathcal{N}$ which recovers the groupoid ring of $\mathcal{E}$ up to isomorphism. Furthermore, we make the somewhat surprising observation that our classification methods naturally transfer to the class of groupoid crossed products, thus providing a classification theory for this class of rings. Our study is motivated by the search for natural examples of groupoid crossed products.

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Natã Machado, Johan Öinert, Stefan Wagner. 2022-07-07. Non-Abelian extensions of groupoids and their groupoid rings. https://doi.org/10.1007/s10485-024-09795-8

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