Prescribed duality dynamics in comodule categories

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Auteur principal: Chirvasitu, Alexandru
Format: Preprint
Publié: 2024
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author Chirvasitu, Alexandru
author_facet Chirvasitu, Alexandru
contents We prove that there exist Hopf algebras with surjective, non-bijective antipode which admit no non-trivial morphisms from Hopf algebras with bijective antipode; in particular, they are not quotients of such. This answers a question left open in prior work, and contrasts with the dual setup whereby a Hopf algebra has injective antipode precisely when it embeds into one with bijective antipode. The examples rely on the broader phenomenon of realizing pre-specified subspace lattices as comodule lattices: for a finite-dimensional vector space $V$ and a sequence $(\mathcal{L}_r)_r$ of successively finer lattices of subspaces thereof, assuming the minimal subquotients of the supremum $\bigvee_r \mathcal{L}_r$ are all at least 2-dimensional, there is a Hopf algebra equipping $V$ with a comodule structure in such a fashion that the lattice of comodules of the $r^{th}$ dual comodule $V^{r*}$ is precisely the given $\mathcal{L}_r$.
format Preprint
id arxiv_https___arxiv_org_abs_2408_08167
institution arXiv
publishDate 2024
record_format arxiv
spellingShingle Prescribed duality dynamics in comodule categories
Chirvasitu, Alexandru
Rings and Algebras
Combinatorics
Category Theory
Quantum Algebra
16S10, 16T05, 16T15, 16T30, 18A40, 18M05
We prove that there exist Hopf algebras with surjective, non-bijective antipode which admit no non-trivial morphisms from Hopf algebras with bijective antipode; in particular, they are not quotients of such. This answers a question left open in prior work, and contrasts with the dual setup whereby a Hopf algebra has injective antipode precisely when it embeds into one with bijective antipode. The examples rely on the broader phenomenon of realizing pre-specified subspace lattices as comodule lattices: for a finite-dimensional vector space $V$ and a sequence $(\mathcal{L}_r)_r$ of successively finer lattices of subspaces thereof, assuming the minimal subquotients of the supremum $\bigvee_r \mathcal{L}_r$ are all at least 2-dimensional, there is a Hopf algebra equipping $V$ with a comodule structure in such a fashion that the lattice of comodules of the $r^{th}$ dual comodule $V^{r*}$ is precisely the given $\mathcal{L}_r$.
title Prescribed duality dynamics in comodule categories
topic Rings and Algebras
Combinatorics
Category Theory
Quantum Algebra
16S10, 16T05, 16T15, 16T30, 18A40, 18M05
url https://arxiv.org/abs/2408.08167