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Article . 2020 . Peer-reviewed
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Involutions of Azumaya Algebras

Involutions of Azumaya algebras
Authors: First, Uriya A.; Williams, Ben;

Involutions of Azumaya Algebras

Abstract

We consider the general circumstance of an Azumaya algebra A of degree n over a locally ringed topos (\mathbf{X}, \mathcal O_\mathbf{X}) where the latter carries a (possibly trivial) involution, denoted \lambda . This generalizes the usual notion of involutions of Azumaya algebras over schemes with involution, which in turn generalizes the notion of involutions of central simple algebras. We provide a criterion to determine whether two Azumaya algebras with involutions extending \lambda are locally isomorphic, describe the equivalence classes obtained by this relation, and settle the question of when an Azumaya algebra A is Brauer equivalent to an algebra carrying an involution extending \lambda , by giving a cohomological condition. We remark that these results are novel even in the case of schemes, since we allow ramified, non-trivial involutions of the base object. We observe that, if the cohomological condition is satisfied, then A is Brauer equivalent to an Azumaya algebra of degree 2n carrying an involution. By comparison with the case of topological spaces, we show that the integer 2n is minimal, even in the case of a nonsingular affine variety X with a fixed-point free involution. As an incidental step, we show that if R is a commutative ring with involution for which the fixed ring S is local, then either R is local or R/S is a quadratic étale extension of rings.

Keywords

Separable algebras (e.g., quaternion algebras, Azumaya algebras, etc.), Bilinear and Hermitian forms, Azumaya algebra, equivariant homotopy theory, ramification, sheaf cohomology, Mathematics - Rings and Algebras, Mathematics - Algebraic Geometry, Brauer group, Rings and Algebras (math.RA), involution, FOS: Mathematics, Algebraic Topology (math.AT), Mathematics - Algebraic Topology, Algebraic Geometry (math.AG), Brauer groups of schemes, Equivariant homotopy theory in algebraic topology

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selected citations
These citations are derived from selected sources.
This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Citations provided by BIP!
popularity
This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network.
BIP!Popularity provided by BIP!
influence
This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Influence provided by BIP!
impulse
This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
BIP!Impulse provided by BIP!
3
Top 10%
Average
Average
Green
Published in a Diamond OA journal