<p>All topological groups appearing in this paper shall be considered Hausdorff. A topological group is <i>minimally almost periodic </i>(<InlineEquation ID="IEq1"> <EquationSource Format="TEX">\({\textrm{MinAP}}\)</EquationSource> <EquationSource Format="MATHML"><math> <mtext>MinAP</mtext> </math></EquationSource> </InlineEquation>) if it admits no non-trivial continuous homomorphism to a compact group. A topological group <i>G</i> is said to have <i>no small normal subgroups</i> <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\((\textrm{NSnS})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <mtext>NSnS</mtext> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> if it admits an open neighbourhood of the identity containing no non-trivial normal subgroups of <i>G</i>. This property is a generalization of the classical <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(\textrm{NSS}\)</EquationSource> <EquationSource Format="MATHML"><math> <mtext>NSS</mtext> </math></EquationSource> </InlineEquation> (:= <i>no small subgroup</i>) property involved in the literature of the historical fifth problem of Hilbert. In this paper we compare three different, but natural generalizations of the <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\({\textrm{MinAP}}\)</EquationSource> <EquationSource Format="MATHML"><math> <mtext>MinAP</mtext> </math></EquationSource> </InlineEquation> groups: the topological groups <i>G</i> which admit no non-trivial continuous homomorphisms to locally compact groups, to Lie groups and to <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(\textrm{NSS}\)</EquationSource> <EquationSource Format="MATHML"><math> <mtext>NSS</mtext> </math></EquationSource> </InlineEquation> groups respectively; we prove that they differ in general. In addition, we give a complete characterization of the topological groups <i>G</i> with the following property: the only <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\(\textrm{NSnS}\)</EquationSource> <EquationSource Format="MATHML"><math> <mtext>NSnS</mtext> </math></EquationSource> </InlineEquation> topological group quotient of <i>G</i> is the trivial group. From this result, we deduce a complete description of the Abelian groups which admit no non-trivial continuous homomorphism to an <InlineEquation ID="IEq7"> <EquationSource Format="TEX">\(\textrm{NSS}\)</EquationSource> <EquationSource Format="MATHML"><math> <mtext>NSS</mtext> </math></EquationSource> </InlineEquation> group, and prove that the family of these groups is the union of all the classes <InlineEquation ID="IEq8"> <EquationSource Format="TEX">\(\texttt{SSGP}(\alpha )\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="monospace">SSGP</mi> <mo stretchy="false">(</mo> <mi>α</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> (where <InlineEquation ID="IEq9"> <EquationSource Format="TEX">\(\alpha \)</EquationSource> <EquationSource Format="MATHML"><math> <mi>α</mi> </math></EquationSource> </InlineEquation> is an ordinal), which were invented by Dikranjan and Shakhmatov in 2016. As a consequence, we prove that an Abelian group <i>G</i> admits a group topology with no non-trivial continuous homomorphism to an <InlineEquation ID="IEq10"> <EquationSource Format="TEX">\(\textrm{NSS}\)</EquationSource> <EquationSource Format="MATHML"><math> <mtext>NSS</mtext> </math></EquationSource> </InlineEquation> group if and only if <i>G</i> admits a group topology with the so-called <i>small subgroup generating property</i> of Gould.</p>

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Generalizing minimal almost periodicity via local compactness, NSS and Lie properties

  • Víctor Hugo Yañez

摘要

All topological groups appearing in this paper shall be considered Hausdorff. A topological group is minimally almost periodic ( \({\textrm{MinAP}}\) MinAP ) if it admits no non-trivial continuous homomorphism to a compact group. A topological group G is said to have no small normal subgroups \((\textrm{NSnS})\) ( NSnS ) if it admits an open neighbourhood of the identity containing no non-trivial normal subgroups of G. This property is a generalization of the classical \(\textrm{NSS}\) NSS (:= no small subgroup) property involved in the literature of the historical fifth problem of Hilbert. In this paper we compare three different, but natural generalizations of the \({\textrm{MinAP}}\) MinAP groups: the topological groups G which admit no non-trivial continuous homomorphisms to locally compact groups, to Lie groups and to \(\textrm{NSS}\) NSS groups respectively; we prove that they differ in general. In addition, we give a complete characterization of the topological groups G with the following property: the only \(\textrm{NSnS}\) NSnS topological group quotient of G is the trivial group. From this result, we deduce a complete description of the Abelian groups which admit no non-trivial continuous homomorphism to an \(\textrm{NSS}\) NSS group, and prove that the family of these groups is the union of all the classes \(\texttt{SSGP}(\alpha )\) SSGP ( α ) (where \(\alpha \) α is an ordinal), which were invented by Dikranjan and Shakhmatov in 2016. As a consequence, we prove that an Abelian group G admits a group topology with no non-trivial continuous homomorphism to an \(\textrm{NSS}\) NSS group if and only if G admits a group topology with the so-called small subgroup generating property of Gould.