Polynomiality of invariants, unimodularity and adapted pairs
Identifieur interne : 000586 ( Istex/Corpus ); précédent : 000585; suivant : 000587Polynomiality of invariants, unimodularity and adapted pairs
Auteurs : Anthony Joseph ; Doron ShafrirSource :
- Transformation Groups [ 1083-4362 ] ; 2010-12-01.
Abstract
Abstract: Let $$ \mathfrak{a} $$ be a finite-dimensional Lie algebra and $$ Y\left( \mathfrak{a} \right) $$ the $$ \mathfrak{a} $$ invariant subalgebra of its symmetric algebra $$ S\left( \mathfrak{a} \right) $$ under adjoint action. Recently there has been considerable interest in studying situations when $$ Y\left( \mathfrak{a} \right) $$ may be polynomial on index $$ \mathfrak{a} $$ generators, for example if $$ \mathfrak{a} $$ is a biparabolic or a centralizer $$ {\mathfrak{g}^x} $$ in a semisimple Lie algebra $$ \mathfrak{g} $$. Here a sum rule of Ooms and Van den Bergh on the degrees d i of the generators is extended to the case when $$ \mathfrak{a} $$ is unimodular and the fundamental semi-invariant $$ {p_\mathfrak{a}} $$ of $$ \mathfrak{a} $$ is an invariant. It is noted that these last two conditions always hold for a centralizer $$ {\mathfrak{g}^x} $$ and moreover that one has GKdim $$ Y\left( {{\mathfrak{g}^x}} \right) $$ = index $$ {\mathfrak{g}^x} $$, even though $$ S\left( {{\mathfrak{g}^x}} \right) $$ may admit proper semi-invariants. Applications are given to the notion of an adapted pair (h, η) for $$ \mathfrak{a} $$. Under the above conditions it is shown that the set of eigenvalues {m i} of -ad h on $$ {\mathfrak{a}^\eta } $$ must equal {(d i - 1)}. This gives rise to a condition under which $$ Y\left( \mathfrak{a} \right) $$ cannot be polynomial on index $$ \mathfrak{a} $$ generators. Finally the theorem of Bolsinov is extended to the case when $$ {p_\mathfrak{a}} $$ is nonscalar.
Url:
DOI: 10.1007/s00031-010-9113-6
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<front><div type="abstract" xml:lang="en">Abstract: Let $$ \mathfrak{a} $$ be a finite-dimensional Lie algebra and $$ Y\left( \mathfrak{a} \right) $$ the $$ \mathfrak{a} $$ invariant subalgebra of its symmetric algebra $$ S\left( \mathfrak{a} \right) $$ under adjoint action. Recently there has been considerable interest in studying situations when $$ Y\left( \mathfrak{a} \right) $$ may be polynomial on index $$ \mathfrak{a} $$ generators, for example if $$ \mathfrak{a} $$ is a biparabolic or a centralizer $$ {\mathfrak{g}^x} $$ in a semisimple Lie algebra $$ \mathfrak{g} $$. Here a sum rule of Ooms and Van den Bergh on the degrees d i of the generators is extended to the case when $$ \mathfrak{a} $$ is unimodular and the fundamental semi-invariant $$ {p_\mathfrak{a}} $$ of $$ \mathfrak{a} $$ is an invariant. It is noted that these last two conditions always hold for a centralizer $$ {\mathfrak{g}^x} $$ and moreover that one has GKdim $$ Y\left( {{\mathfrak{g}^x}} \right) $$ = index $$ {\mathfrak{g}^x} $$, even though $$ S\left( {{\mathfrak{g}^x}} \right) $$ may admit proper semi-invariants. Applications are given to the notion of an adapted pair (h, η) for $$ \mathfrak{a} $$. Under the above conditions it is shown that the set of eigenvalues {m i} of -ad h on $$ {\mathfrak{a}^\eta } $$ must equal {(d i - 1)}. This gives rise to a condition under which $$ Y\left( \mathfrak{a} \right) $$ cannot be polynomial on index $$ \mathfrak{a} $$ generators. Finally the theorem of Bolsinov is extended to the case when $$ {p_\mathfrak{a}} $$ is nonscalar.</div>
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<EquationSource Format="TEX">$$ \mathfrak{a} $$</EquationSource>
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be a finite-dimensional Lie algebra and <InlineEquation ID="IEq2"><InlineMediaObject><ImageObject FileRef="31_2010_9113_Article_IEq2.gif" Format="GIF" Color="BlackWhite" Type="Linedraw" Rendition="HTML"></ImageObject>
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<EquationSource Format="TEX">$$ Y\left( \mathfrak{a} \right) $$</EquationSource>
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the <InlineEquation ID="IEq3"><InlineMediaObject><ImageObject FileRef="31_2010_9113_Article_IEq3.gif" Format="GIF" Color="BlackWhite" Type="Linedraw" Rendition="HTML"></ImageObject>
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<EquationSource Format="TEX">$$ \mathfrak{a} $$</EquationSource>
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invariant subalgebra of its symmetric algebra <InlineEquation ID="IEq4"><InlineMediaObject><ImageObject FileRef="31_2010_9113_Article_IEq4.gif" Format="GIF" Color="BlackWhite" Type="Linedraw" Rendition="HTML"></ImageObject>
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<EquationSource Format="TEX">$$ S\left( \mathfrak{a} \right) $$</EquationSource>
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under adjoint action. Recently there has been considerable interest in studying situations when <InlineEquation ID="IEq5"><InlineMediaObject><ImageObject FileRef="31_2010_9113_Article_IEq5.gif" Format="GIF" Color="BlackWhite" Type="Linedraw" Rendition="HTML"></ImageObject>
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<EquationSource Format="TEX">$$ Y\left( \mathfrak{a} \right) $$</EquationSource>
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may be polynomial on index <InlineEquation ID="IEq6"><InlineMediaObject><ImageObject FileRef="31_2010_9113_Article_IEq6.gif" Format="GIF" Color="BlackWhite" Type="Linedraw" Rendition="HTML"></ImageObject>
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<EquationSource Format="TEX">$$ \mathfrak{a} $$</EquationSource>
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generators, for example if <InlineEquation ID="IEq100"><InlineMediaObject><ImageObject FileRef="31_2010_9113_Article_IEq100.gif" Format="GIF" Color="BlackWhite" Type="Linedraw" Rendition="HTML"></ImageObject>
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<EquationSource Format="TEX">$$ \mathfrak{a} $$</EquationSource>
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is a biparabolic or a centralizer <InlineEquation ID="IEq7"><InlineMediaObject><ImageObject FileRef="31_2010_9113_Article_IEq7.gif" Format="GIF" Color="BlackWhite" Type="Linedraw" Rendition="HTML"></ImageObject>
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<EquationSource Format="TEX">$$ {\mathfrak{g}^x} $$</EquationSource>
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in a semisimple Lie algebra <InlineEquation ID="IEq8"><InlineMediaObject><ImageObject FileRef="31_2010_9113_Article_IEq8.gif" Format="GIF" Color="BlackWhite" Type="Linedraw" Rendition="HTML"></ImageObject>
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<EquationSource Format="TEX">$$ \mathfrak{g} $$</EquationSource>
</InlineEquation>
.</Para>
<Para>Here a sum rule of Ooms and Van den Bergh on the degrees <Emphasis Type="Italic">d</Emphasis>
<Subscript><Emphasis Type="Italic">i</Emphasis>
</Subscript>
of the generators is extended to the case when <InlineEquation ID="IEq9"><InlineMediaObject><ImageObject FileRef="31_2010_9113_Article_IEq9.gif" Format="GIF" Color="BlackWhite" Type="Linedraw" Rendition="HTML"></ImageObject>
</InlineMediaObject>
<EquationSource Format="TEX">$$ \mathfrak{a} $$</EquationSource>
</InlineEquation>
is unimodular and the fundamental semi-invariant <InlineEquation ID="IEq10"><InlineMediaObject><ImageObject FileRef="31_2010_9113_Article_IEq10.gif" Format="GIF" Color="BlackWhite" Type="Linedraw" Rendition="HTML"></ImageObject>
</InlineMediaObject>
<EquationSource Format="TEX">$$ {p_\mathfrak{a}} $$</EquationSource>
</InlineEquation>
of <InlineEquation ID="IEq11"><InlineMediaObject><ImageObject FileRef="31_2010_9113_Article_IEq11.gif" Format="GIF" Color="BlackWhite" Type="Linedraw" Rendition="HTML"></ImageObject>
</InlineMediaObject>
<EquationSource Format="TEX">$$ \mathfrak{a} $$</EquationSource>
</InlineEquation>
is an invariant. It is noted that these last two conditions always hold for a centralizer <InlineEquation ID="IEq12"><InlineMediaObject><ImageObject FileRef="31_2010_9113_Article_IEq12.gif" Format="GIF" Color="BlackWhite" Type="Linedraw" Rendition="HTML"></ImageObject>
</InlineMediaObject>
<EquationSource Format="TEX">$$ {\mathfrak{g}^x} $$</EquationSource>
</InlineEquation>
and moreover that one has GKdim <InlineEquation ID="IEq13"><InlineMediaObject><ImageObject FileRef="31_2010_9113_Article_IEq13.gif" Format="GIF" Color="BlackWhite" Type="Linedraw" Rendition="HTML"></ImageObject>
</InlineMediaObject>
<EquationSource Format="TEX">$$ Y\left( {{\mathfrak{g}^x}} \right) $$</EquationSource>
</InlineEquation>
= index <InlineEquation ID="IEq14"><InlineMediaObject><ImageObject FileRef="31_2010_9113_Article_IEq14.gif" Format="GIF" Color="BlackWhite" Type="Linedraw" Rendition="HTML"></ImageObject>
</InlineMediaObject>
<EquationSource Format="TEX">$$ {\mathfrak{g}^x} $$</EquationSource>
</InlineEquation>
, even though <InlineEquation ID="IEq15"><InlineMediaObject><ImageObject FileRef="31_2010_9113_Article_IEq15.gif" Format="GIF" Color="BlackWhite" Type="Linedraw" Rendition="HTML"></ImageObject>
</InlineMediaObject>
<EquationSource Format="TEX">$$ S\left( {{\mathfrak{g}^x}} \right) $$</EquationSource>
</InlineEquation>
may admit proper semi-invariants.</Para>
<Para>Applications are given to the notion of an adapted pair (<Emphasis Type="Italic">h</Emphasis>
, η) for <InlineEquation ID="IEq16"><InlineMediaObject><ImageObject FileRef="31_2010_9113_Article_IEq16.gif" Format="GIF" Color="BlackWhite" Type="Linedraw" Rendition="HTML"></ImageObject>
</InlineMediaObject>
<EquationSource Format="TEX">$$ \mathfrak{a} $$</EquationSource>
</InlineEquation>
. Under the above conditions it is shown that the set of eigenvalues {<Emphasis Type="Italic">m</Emphasis>
<Subscript><Emphasis Type="Italic">i</Emphasis>
</Subscript>
} of -ad <Emphasis Type="Italic">h</Emphasis>
on <InlineEquation ID="IEq17"><InlineMediaObject><ImageObject FileRef="31_2010_9113_Article_IEq17.gif" Format="GIF" Color="BlackWhite" Type="Linedraw" Rendition="HTML"></ImageObject>
</InlineMediaObject>
<EquationSource Format="TEX">$$ {\mathfrak{a}^\eta } $$</EquationSource>
</InlineEquation>
must equal {(<Emphasis Type="Italic">d</Emphasis>
<Subscript><Emphasis Type="Italic">i</Emphasis>
</Subscript>
- 1)}. This gives rise to a condition under which <InlineEquation ID="IEq18"><InlineMediaObject><ImageObject FileRef="31_2010_9113_Article_IEq18.gif" Format="GIF" Color="BlackWhite" Type="Linedraw" Rendition="HTML"></ImageObject>
</InlineMediaObject>
<EquationSource Format="TEX">$$ Y\left( \mathfrak{a} \right) $$</EquationSource>
</InlineEquation>
cannot be polynomial on index <InlineEquation ID="IEq101"><InlineMediaObject><ImageObject FileRef="31_2010_9113_Article_IEq101.gif" Format="GIF" Color="BlackWhite" Type="Linedraw" Rendition="HTML"></ImageObject>
</InlineMediaObject>
<EquationSource Format="TEX">$$ \mathfrak{a} $$</EquationSource>
</InlineEquation>
generators.</Para>
<Para>Finally the theorem of Bolsinov is extended to the case when <InlineEquation ID="IEq19"><InlineMediaObject><ImageObject FileRef="31_2010_9113_Article_IEq19.gif" Format="GIF" Color="BlackWhite" Type="Linedraw" Rendition="HTML"></ImageObject>
</InlineMediaObject>
<EquationSource Format="TEX">$$ {p_\mathfrak{a}} $$</EquationSource>
</InlineEquation>
is nonscalar.</Para>
</Abstract>
<ArticleNote Type="Dedication"><SimplePara>Dedicated to Vladimir Morozov on the 100th anniversary of his birthday</SimplePara>
</ArticleNote>
<ArticleNote Type="Misc"><SimplePara>Supported in part by Minerva grant, no. 8596/1.</SimplePara>
</ArticleNote>
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<NoBody></NoBody>
</Article>
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<mods version="3.6"><titleInfo lang="en"><title>Polynomiality of invariants, unimodularity and adapted pairs</title>
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<titleInfo type="alternative" contentType="CDATA" lang="en"><title>Polynomiality of invariants, unimodularity and adapted pairs</title>
</titleInfo>
<name type="personal" displayLabel="corresp"><namePart type="given">Anthony</namePart>
<namePart type="family">Joseph</namePart>
<affiliation>Donald Frey Professional Chair, Department of Mathematics, Weizmann Institute of Science, 76100, Rehovot, Israel</affiliation>
<affiliation>E-mail: anthony.joseph@weizmann.ac.il</affiliation>
<role><roleTerm type="text">author</roleTerm>
</role>
</name>
<name type="personal"><namePart type="given">Doron</namePart>
<namePart type="family">Shafrir</namePart>
<affiliation>Department of Mathematics, Hebrew University, Givat Ram, 91904, Jerusalem, Israel</affiliation>
<affiliation>E-mail: doron.abc@gmail.com</affiliation>
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<originInfo><publisher>SP Birkhäuser Verlag Boston</publisher>
<place><placeTerm type="text">Boston</placeTerm>
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<dateCreated encoding="w3cdtf">2010-01-12</dateCreated>
<dateIssued encoding="w3cdtf">2010-12-01</dateIssued>
<dateIssued encoding="w3cdtf">2010</dateIssued>
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<language><languageTerm type="code" authority="rfc3066">en</languageTerm>
<languageTerm type="code" authority="iso639-2b">eng</languageTerm>
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<abstract lang="en">Abstract: Let $$ \mathfrak{a} $$ be a finite-dimensional Lie algebra and $$ Y\left( \mathfrak{a} \right) $$ the $$ \mathfrak{a} $$ invariant subalgebra of its symmetric algebra $$ S\left( \mathfrak{a} \right) $$ under adjoint action. Recently there has been considerable interest in studying situations when $$ Y\left( \mathfrak{a} \right) $$ may be polynomial on index $$ \mathfrak{a} $$ generators, for example if $$ \mathfrak{a} $$ is a biparabolic or a centralizer $$ {\mathfrak{g}^x} $$ in a semisimple Lie algebra $$ \mathfrak{g} $$. Here a sum rule of Ooms and Van den Bergh on the degrees d i of the generators is extended to the case when $$ \mathfrak{a} $$ is unimodular and the fundamental semi-invariant $$ {p_\mathfrak{a}} $$ of $$ \mathfrak{a} $$ is an invariant. It is noted that these last two conditions always hold for a centralizer $$ {\mathfrak{g}^x} $$ and moreover that one has GKdim $$ Y\left( {{\mathfrak{g}^x}} \right) $$ = index $$ {\mathfrak{g}^x} $$, even though $$ S\left( {{\mathfrak{g}^x}} \right) $$ may admit proper semi-invariants. Applications are given to the notion of an adapted pair (h, η) for $$ \mathfrak{a} $$. Under the above conditions it is shown that the set of eigenvalues {m i} of -ad h on $$ {\mathfrak{a}^\eta } $$ must equal {(d i - 1)}. This gives rise to a condition under which $$ Y\left( \mathfrak{a} \right) $$ cannot be polynomial on index $$ \mathfrak{a} $$ generators. Finally the theorem of Bolsinov is extended to the case when $$ {p_\mathfrak{a}} $$ is nonscalar.</abstract>
<relatedItem type="host"><titleInfo><title>Transformation Groups</title>
</titleInfo>
<titleInfo type="abbreviated"><title>Transformation Groups</title>
</titleInfo>
<genre type="journal" displayLabel="Non Standard Archive Journal" authority="ISTEX" authorityURI="https://publication-type.data.istex.fr" valueURI="https://publication-type.data.istex.fr/ark:/67375/JMC-0GLKJH51-B">journal</genre>
<originInfo><publisher>Springer</publisher>
<dateIssued encoding="w3cdtf">2010-12-17</dateIssued>
<copyrightDate encoding="w3cdtf">2010</copyrightDate>
</originInfo>
<subject><genre>Mathematics</genre>
<topic>Algebra</topic>
<topic>Topological Groups, Lie Groups</topic>
</subject>
<identifier type="ISSN">1083-4362</identifier>
<identifier type="eISSN">1531-586X</identifier>
<identifier type="JournalID">31</identifier>
<identifier type="IssueArticleCount">13</identifier>
<identifier type="VolumeIssueCount">4</identifier>
<part><date>2010</date>
<detail type="volume"><number>15</number>
<caption>vol.</caption>
</detail>
<detail type="issue"><number>4</number>
<caption>no.</caption>
</detail>
<extent unit="pages"><start>851</start>
<end>882</end>
</extent>
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<identifier type="DOI">10.1007/s00031-010-9113-6</identifier>
<identifier type="ArticleID">9113</identifier>
<identifier type="ArticleID">s00031-010-9113-6</identifier>
<accessCondition type="use and reproduction" contentType="copyright">Springer Science+Business Media, LLC, 2010</accessCondition>
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