{"title":"Algebras defined by Lyndon words and Artin-Schelter regularity","authors":"T. Gateva-Ivanova","doi":"10.1090/btran/89","DOIUrl":null,"url":null,"abstract":"<p>Let <inline-formula content-type=\"math/mathml\">\n<mml:math xmlns:mml=\"http://www.w3.org/1998/Math/MathML\" alttext=\"upper X equals StartSet x 1 comma x 2 comma midline-horizontal-ellipsis comma x Subscript n Baseline EndSet\">\n <mml:semantics>\n <mml:mrow>\n <mml:mi>X</mml:mi>\n <mml:mo>=</mml:mo>\n <mml:mo fence=\"false\" stretchy=\"false\">{</mml:mo>\n <mml:msub>\n <mml:mi>x</mml:mi>\n <mml:mn>1</mml:mn>\n </mml:msub>\n <mml:mo>,</mml:mo>\n <mml:msub>\n <mml:mi>x</mml:mi>\n <mml:mn>2</mml:mn>\n </mml:msub>\n <mml:mo>,</mml:mo>\n <mml:mo>⋯<!-- ⋯ --></mml:mo>\n <mml:mo>,</mml:mo>\n <mml:msub>\n <mml:mi>x</mml:mi>\n <mml:mi>n</mml:mi>\n </mml:msub>\n <mml:mo fence=\"false\" stretchy=\"false\">}</mml:mo>\n </mml:mrow>\n <mml:annotation encoding=\"application/x-tex\">X= \\{x_1, x_2, \\cdots , x_n\\}</mml:annotation>\n </mml:semantics>\n</mml:math>\n</inline-formula> be a finite alphabet, and let <inline-formula content-type=\"math/mathml\">\n<mml:math xmlns:mml=\"http://www.w3.org/1998/Math/MathML\" alttext=\"upper K\">\n <mml:semantics>\n <mml:mi>K</mml:mi>\n <mml:annotation encoding=\"application/x-tex\">K</mml:annotation>\n </mml:semantics>\n</mml:math>\n</inline-formula> be a field. We study classes <inline-formula content-type=\"math/mathml\">\n<mml:math xmlns:mml=\"http://www.w3.org/1998/Math/MathML\" alttext=\"German upper C left-parenthesis upper X comma upper W right-parenthesis\">\n <mml:semantics>\n <mml:mrow>\n <mml:mrow class=\"MJX-TeXAtom-ORD\">\n <mml:mi mathvariant=\"fraktur\">C</mml:mi>\n </mml:mrow>\n <mml:mo stretchy=\"false\">(</mml:mo>\n <mml:mi>X</mml:mi>\n <mml:mo>,</mml:mo>\n <mml:mi>W</mml:mi>\n <mml:mo stretchy=\"false\">)</mml:mo>\n </mml:mrow>\n <mml:annotation encoding=\"application/x-tex\">\\mathfrak {C}(X, W)</mml:annotation>\n </mml:semantics>\n</mml:math>\n</inline-formula> of graded <inline-formula content-type=\"math/mathml\">\n<mml:math xmlns:mml=\"http://www.w3.org/1998/Math/MathML\" alttext=\"upper K\">\n <mml:semantics>\n <mml:mi>K</mml:mi>\n <mml:annotation encoding=\"application/x-tex\">K</mml:annotation>\n </mml:semantics>\n</mml:math>\n</inline-formula>-algebras <inline-formula content-type=\"math/mathml\">\n<mml:math xmlns:mml=\"http://www.w3.org/1998/Math/MathML\" alttext=\"upper A equals upper K mathematical left-angle upper X mathematical right-angle slash upper I\">\n <mml:semantics>\n <mml:mrow>\n <mml:mi>A</mml:mi>\n <mml:mo>=</mml:mo>\n <mml:mi>K</mml:mi>\n <mml:mo fence=\"false\" stretchy=\"false\">⟨<!-- ⟨ --></mml:mo>\n <mml:mi>X</mml:mi>\n <mml:mo fence=\"false\" stretchy=\"false\">⟩<!-- ⟩ --></mml:mo>\n <mml:mrow class=\"MJX-TeXAtom-ORD\">\n <mml:mo>/</mml:mo>\n </mml:mrow>\n <mml:mi>I</mml:mi>\n </mml:mrow>\n <mml:annotation encoding=\"application/x-tex\">A = K\\langle X\\rangle / I</mml:annotation>\n </mml:semantics>\n</mml:math>\n</inline-formula>, generated by <inline-formula content-type=\"math/mathml\">\n<mml:math xmlns:mml=\"http://www.w3.org/1998/Math/MathML\" alttext=\"upper X\">\n <mml:semantics>\n <mml:mi>X</mml:mi>\n <mml:annotation encoding=\"application/x-tex\">X</mml:annotation>\n </mml:semantics>\n</mml:math>\n</inline-formula> and with <italic>a fixed set of obstructions</italic> <inline-formula content-type=\"math/mathml\">\n<mml:math xmlns:mml=\"http://www.w3.org/1998/Math/MathML\" alttext=\"upper W\">\n <mml:semantics>\n <mml:mi>W</mml:mi>\n <mml:annotation encoding=\"application/x-tex\">W</mml:annotation>\n </mml:semantics>\n</mml:math>\n</inline-formula>. Initially we do not impose restrictions on <inline-formula content-type=\"math/mathml\">\n<mml:math xmlns:mml=\"http://www.w3.org/1998/Math/MathML\" alttext=\"upper W\">\n <mml:semantics>\n <mml:mi>W</mml:mi>\n <mml:annotation encoding=\"application/x-tex\">W</mml:annotation>\n </mml:semantics>\n</mml:math>\n</inline-formula> and investigate the case when the algebras in <inline-formula content-type=\"math/mathml\">\n<mml:math xmlns:mml=\"http://www.w3.org/1998/Math/MathML\" alttext=\"German upper C left-parenthesis upper X comma upper W right-parenthesis\">\n <mml:semantics>\n <mml:mrow>\n <mml:mrow class=\"MJX-TeXAtom-ORD\">\n <mml:mi mathvariant=\"fraktur\">C</mml:mi>\n </mml:mrow>\n <mml:mo stretchy=\"false\">(</mml:mo>\n <mml:mi>X</mml:mi>\n <mml:mo>,</mml:mo>\n <mml:mi>W</mml:mi>\n <mml:mo stretchy=\"false\">)</mml:mo>\n </mml:mrow>\n <mml:annotation encoding=\"application/x-tex\">\\mathfrak {C} (X, W)</mml:annotation>\n </mml:semantics>\n</mml:math>\n</inline-formula> have polynomial growth and finite global dimension <inline-formula content-type=\"math/mathml\">\n<mml:math xmlns:mml=\"http://www.w3.org/1998/Math/MathML\" alttext=\"d\">\n <mml:semantics>\n <mml:mi>d</mml:mi>\n <mml:annotation encoding=\"application/x-tex\">d</mml:annotation>\n </mml:semantics>\n</mml:math>\n</inline-formula>. Next we consider classes <inline-formula content-type=\"math/mathml\">\n<mml:math xmlns:mml=\"http://www.w3.org/1998/Math/MathML\" alttext=\"German upper C left-parenthesis upper X comma upper W right-parenthesis\">\n <mml:semantics>\n <mml:mrow>\n <mml:mrow class=\"MJX-TeXAtom-ORD\">\n <mml:mi mathvariant=\"fraktur\">C</mml:mi>\n </mml:mrow>\n <mml:mo stretchy=\"false\">(</mml:mo>\n <mml:mi>X</mml:mi>\n <mml:mo>,</mml:mo>\n <mml:mi>W</mml:mi>\n <mml:mo stretchy=\"false\">)</mml:mo>\n </mml:mrow>\n <mml:annotation encoding=\"application/x-tex\">\\mathfrak {C} (X, W)</mml:annotation>\n </mml:semantics>\n</mml:math>\n</inline-formula> of algebras whose sets of obstructions <inline-formula content-type=\"math/mathml\">\n<mml:math xmlns:mml=\"http://www.w3.org/1998/Math/MathML\" alttext=\"upper W\">\n <mml:semantics>\n <mml:mi>W</mml:mi>\n <mml:annotation encoding=\"application/x-tex\">W</mml:annotation>\n </mml:semantics>\n</mml:math>\n</inline-formula> are antichains of Lyndon words. The central question is “<italic>when a class <inline-formula content-type=\"math/mathml\">\n<mml:math xmlns:mml=\"http://www.w3.org/1998/Math/MathML\" alttext=\"German upper C left-parenthesis upper X comma upper W right-parenthesis\">\n <mml:semantics>\n <mml:mrow>\n <mml:mrow class=\"MJX-TeXAtom-ORD\">\n <mml:mi mathvariant=\"fraktur\">C</mml:mi>\n </mml:mrow>\n <mml:mo stretchy=\"false\">(</mml:mo>\n <mml:mi>X</mml:mi>\n <mml:mo>,</mml:mo>\n <mml:mi>W</mml:mi>\n <mml:mo stretchy=\"false\">)</mml:mo>\n </mml:mrow>\n <mml:annotation encoding=\"application/x-tex\">\\mathfrak {C} (X, W)</mml:annotation>\n </mml:semantics>\n</mml:math>\n</inline-formula> contains Artin-Schelter regular algebras?</italic>” Each class <inline-formula content-type=\"math/mathml\">\n<mml:math xmlns:mml=\"http://www.w3.org/1998/Math/MathML\" alttext=\"German upper C left-parenthesis upper X comma upper W right-parenthesis\">\n <mml:semantics>\n <mml:mrow>\n <mml:mrow class=\"MJX-TeXAtom-ORD\">\n <mml:mi mathvariant=\"fraktur\">C</mml:mi>\n </mml:mrow>\n <mml:mo stretchy=\"false\">(</mml:mo>\n <mml:mi>X</mml:mi>\n <mml:mo>,</mml:mo>\n <mml:mi>W</mml:mi>\n <mml:mo stretchy=\"false\">)</mml:mo>\n </mml:mrow>\n <mml:annotation encoding=\"application/x-tex\">\\mathfrak {C} (X, W)</mml:annotation>\n </mml:semantics>\n</mml:math>\n</inline-formula> defines a Lyndon pair <inline-formula content-type=\"math/mathml\">\n<mml:math xmlns:mml=\"http://www.w3.org/1998/Math/MathML\" alttext=\"left-parenthesis upper N comma upper W right-parenthesis\">\n <mml:semantics>\n <mml:mrow>\n <mml:mo stretchy=\"false\">(</mml:mo>\n <mml:mi>N</mml:mi>\n <mml:mo>,</mml:mo>\n <mml:mi>W</mml:mi>\n <mml:mo stretchy=\"false\">)</mml:mo>\n </mml:mrow>\n <mml:annotation encoding=\"application/x-tex\">(N,W)</mml:annotation>\n </mml:semantics>\n</mml:math>\n</inline-formula>, which, if <inline-formula content-type=\"math/mathml\">\n<mml:math xmlns:mml=\"http://www.w3.org/1998/Math/MathML\" alttext=\"upper N\">\n <mml:semantics>\n <mml:mi>N</mml:mi>\n <mml:annotation encoding=\"application/x-tex\">N</mml:annotation>\n </mml:semantics>\n</mml:math>\n</inline-formula> is finite, determines uniquely the global dimension, <inline-formula content-type=\"math/mathml\">\n<mml:math xmlns:mml=\"http://www.w3.org/1998/Math/MathML\" alttext=\"g l d i m upper A\">\n <mml:semantics>\n <mml:mrow>\n <mml:mi>g</mml:mi>\n <mml:mi>l</mml:mi>\n <mml:mspace width=\"thinmathspace\" />\n <mml:mi>d</mml:mi>\n <mml:mi>i</mml:mi>\n <mml:mi>m</mml:mi>\n <mml:mi>A</mml:mi>\n </mml:mrow>\n <mml:annotation encoding=\"application/x-tex\">gl\\,dimA</mml:annotation>\n </mml:semantics>\n</mml:math>\n</inline-formula>, and the Gelfand-Kirillov dimension, <inline-formula content-type=\"math/mathml\">\n<mml:math xmlns:mml=\"http://www.w3.org/1998/Math/MathML\" alttext=\"upper G upper K d i m upper A\">\n <mml:semantics>\n <mml:mrow>\n <mml:mi>G</mml:mi>\n <mml:mi>K</mml:mi>\n <mml:mi>d</mml:mi>\n <mml:mi>i</mml:mi>\n <mml:mi>m</mml:mi>\n <mml:mi>A</mml:mi>\n </mml:mrow>\n <mml:annotation encoding=\"application/x-tex\">GK dimA</mml:annotation>\n </mml:semantics>\n</mml:math>\n</inline-formula>, for every <inline-formula content-type=\"math/mathml\">\n<mml:math xmlns:mml=\"http://www.w3.org/1998/Math/MathML\" alttext=\"upper A element-of German upper C left-parenthesis upper X comma upper W right-parenthesis\">\n <mml:semantics>\n <mml:mrow>\n <mml:mi>A</mml:mi>\n <mml:mo>∈<!-- ∈ --></mml:mo>\n <mml:mrow class=\"MJX-TeXAtom-ORD\">\n <mml:mi mathvariant=\"fraktur\">C</mml:mi>\n </mml:mrow>\n <mml:mo stretchy=\"false\">(</mml:mo>\n <mml:mi>X</mml:mi>\n <mml:mo>,</mml:mo>\n <mml:mi>W</mml:mi>\n <mml:mo stretchy=\"false\">)</mml:mo>\n </mml:mrow>\n <mml:annotation encoding=\"application/x-tex\">A \\in \\mathfrak {C}(X, W)</mml:annotation>\n </mml:semantics>\n</mml:math>\n</inline-formula>. We find a combinatorial condition in terms of <inline-formula content-type=\"math/mathml\">\n<mml:mat","PeriodicalId":377306,"journal":{"name":"Transactions of the American Mathematical Society, Series B","volume":"46 5","pages":"0"},"PeriodicalIF":0.0000,"publicationDate":"2019-05-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"3","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Transactions of the American Mathematical Society, Series B","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/10.1090/btran/89","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
引用次数: 3
Abstract
Let X={x1,x2,⋯,xn}X= \{x_1, x_2, \cdots , x_n\} be a finite alphabet, and let KK be a field. We study classes C(X,W)\mathfrak {C}(X, W) of graded KK-algebras A=K⟨X⟩/IA = K\langle X\rangle / I, generated by XX and with a fixed set of obstructionsWW. Initially we do not impose restrictions on WW and investigate the case when the algebras in C(X,W)\mathfrak {C} (X, W) have polynomial growth and finite global dimension dd. Next we consider classes C(X,W)\mathfrak {C} (X, W) of algebras whose sets of obstructions WW are antichains of Lyndon words. The central question is “when a class C(X,W)\mathfrak {C} (X, W) contains Artin-Schelter regular algebras?” Each class C(X,W)\mathfrak {C} (X, W) defines a Lyndon pair (N,W)(N,W), which, if NN is finite, determines uniquely the global dimension, gldimAgl\,dimA, and the Gelfand-Kirillov dimension, GKdimAGK dimA, for every A∈C(X,W)A \in \mathfrak {C}(X, W). We find a combinatorial condition in terms of