Splines on Cayley graphs of the symmetric group

A spline is an assignment of polynomials to the vertices of a graph whose edges are labeled by ideals, where the difference of two polynomials labeling adjacent vertices must belong to the corresponding ideal. The set of splines forms a ring. We consider spline rings where the underlying graph is th...

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Main Author: Nathan R. T. Lesnevich
Format: Article
Language:English
Published: Cambridge University Press 2025-01-01
Series:Forum of Mathematics, Sigma
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Online Access:https://www.cambridge.org/core/product/identifier/S2050509425100376/type/journal_article
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author Nathan R. T. Lesnevich
author_facet Nathan R. T. Lesnevich
author_sort Nathan R. T. Lesnevich
collection DOAJ
description A spline is an assignment of polynomials to the vertices of a graph whose edges are labeled by ideals, where the difference of two polynomials labeling adjacent vertices must belong to the corresponding ideal. The set of splines forms a ring. We consider spline rings where the underlying graph is the Cayley graph of a symmetric group generated by a collection of transpositions. These rings generalize the GKM construction for equivariant cohomology rings of flag, regular semisimple Hessenberg and permutohedral varieties. These cohomology rings carry two actions of the symmetric group $S_n$ whose graded characters are both of general interest in algebraic combinatorics. In this paper, we generalize the graded $S_n$ -representations from the cohomologies of the above varieties to splines on Cayley graphs of $S_n$ and then (1) give explicit module and ring generators for whenever the $S_n$ -generating set is minimal, (2) give a combinatorial characterization of when graded pieces of one $S_n$ -representation is trivial, and (3) compute the first degree piece of both graded characters for all generating sets.
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spelling doaj-art-b0557b20072442cd86a8fd0262ee2fd72025-08-20T02:21:46ZengCambridge University PressForum of Mathematics, Sigma2050-50942025-01-011310.1017/fms.2025.10037Splines on Cayley graphs of the symmetric groupNathan R. T. Lesnevich0https://orcid.org/0009-0006-9395-4103https://ror.org/01yc7t268Oklahoma State University, 401 Mathematical Sciences, Stillwater, OK 74078, United StatesA spline is an assignment of polynomials to the vertices of a graph whose edges are labeled by ideals, where the difference of two polynomials labeling adjacent vertices must belong to the corresponding ideal. The set of splines forms a ring. We consider spline rings where the underlying graph is the Cayley graph of a symmetric group generated by a collection of transpositions. These rings generalize the GKM construction for equivariant cohomology rings of flag, regular semisimple Hessenberg and permutohedral varieties. These cohomology rings carry two actions of the symmetric group $S_n$ whose graded characters are both of general interest in algebraic combinatorics. In this paper, we generalize the graded $S_n$ -representations from the cohomologies of the above varieties to splines on Cayley graphs of $S_n$ and then (1) give explicit module and ring generators for whenever the $S_n$ -generating set is minimal, (2) give a combinatorial characterization of when graded pieces of one $S_n$ -representation is trivial, and (3) compute the first degree piece of both graded characters for all generating sets.https://www.cambridge.org/core/product/identifier/S2050509425100376/type/journal_article05E1005C2520C3005E05
spellingShingle Nathan R. T. Lesnevich
Splines on Cayley graphs of the symmetric group
Forum of Mathematics, Sigma
05E10
05C25
20C30
05E05
title Splines on Cayley graphs of the symmetric group
title_full Splines on Cayley graphs of the symmetric group
title_fullStr Splines on Cayley graphs of the symmetric group
title_full_unstemmed Splines on Cayley graphs of the symmetric group
title_short Splines on Cayley graphs of the symmetric group
title_sort splines on cayley graphs of the symmetric group
topic 05E10
05C25
20C30
05E05
url https://www.cambridge.org/core/product/identifier/S2050509425100376/type/journal_article
work_keys_str_mv AT nathanrtlesnevich splinesoncayleygraphsofthesymmetricgroup