<p>Complexes of groups are the natural generalizations of graphs of groups. Let <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(({\mathcal {G}},{\mathcal {Y}})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <mi mathvariant="script">G</mi> <mo>,</mo> <mi mathvariant="script">Y</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> be a developable complex of hyperbolic groups over a finite simplicial complex <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\({\mathcal {Y}}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="script">Y</mi> </math></EquationSource> </InlineEquation> such that the edge groups are finite, and the universal cover of <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(({\mathcal {G}},{\mathcal {Y}})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <mi mathvariant="script">G</mi> <mo>,</mo> <mi mathvariant="script">Y</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> is a hyperbolic space. In the first part of this note, we describe uniform quasigeodesics in the complex of spaces associated to <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(({\mathcal {G}},{\mathcal {Y}})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <mi mathvariant="script">G</mi> <mo>,</mo> <mi mathvariant="script">Y</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation>. In the second part, we investigate the local quasiconvexity of the fundamental group of certain complexes of locally quasiconvex groups with finite edge groups. Specifically, suppose <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\({\mathcal {Y}}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="script">Y</mi> </math></EquationSource> </InlineEquation> is either a Euclidean polygon with at least four sides or a finite CAT(0) square complex. Consider a complex of groups <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\(({\mathcal {G}},{\mathcal {Y}})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <mi mathvariant="script">G</mi> <mo>,</mo> <mi mathvariant="script">Y</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> in which all the vertex groups are locally quasiconvex and hyperbolic, all the edge groups are finite, and the universal cover of <InlineEquation ID="IEq7"> <EquationSource Format="TEX">\(({\mathcal {G}},{\mathcal {Y}})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <mi mathvariant="script">G</mi> <mo>,</mo> <mi mathvariant="script">Y</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> is a hyperbolic space. We prove that the fundamental group of <InlineEquation ID="IEq8"> <EquationSource Format="TEX">\(({\mathcal {G}},{\mathcal {Y}})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <mi mathvariant="script">G</mi> <mo>,</mo> <mi mathvariant="script">Y</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> is locally quasiconvex if and only if it satisfies the Howson property. Finally, we conclude the paper by discussing relevant applications in the last section.</p>

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A Remark on Complexes of hyperbolic Groups with finite edge groups

  • Ravi Tomar

摘要

Complexes of groups are the natural generalizations of graphs of groups. Let \(({\mathcal {G}},{\mathcal {Y}})\) ( G , Y ) be a developable complex of hyperbolic groups over a finite simplicial complex \({\mathcal {Y}}\) Y such that the edge groups are finite, and the universal cover of \(({\mathcal {G}},{\mathcal {Y}})\) ( G , Y ) is a hyperbolic space. In the first part of this note, we describe uniform quasigeodesics in the complex of spaces associated to \(({\mathcal {G}},{\mathcal {Y}})\) ( G , Y ) . In the second part, we investigate the local quasiconvexity of the fundamental group of certain complexes of locally quasiconvex groups with finite edge groups. Specifically, suppose \({\mathcal {Y}}\) Y is either a Euclidean polygon with at least four sides or a finite CAT(0) square complex. Consider a complex of groups \(({\mathcal {G}},{\mathcal {Y}})\) ( G , Y ) in which all the vertex groups are locally quasiconvex and hyperbolic, all the edge groups are finite, and the universal cover of \(({\mathcal {G}},{\mathcal {Y}})\) ( G , Y ) is a hyperbolic space. We prove that the fundamental group of \(({\mathcal {G}},{\mathcal {Y}})\) ( G , Y ) is locally quasiconvex if and only if it satisfies the Howson property. Finally, we conclude the paper by discussing relevant applications in the last section.