<p>We consider manifolds with almost non-negative Ricci curvature and strictly positive integral lower bounds on the sum of the lowest <i>k</i> eigenvalues of the Ricci tensor. If <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\((M^n,g)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <msup> <mi>M</mi> <mi>n</mi> </msup> <mo>,</mo> <mi>g</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> is a Riemannian manifold satisfying such curvature bounds for <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(k=2\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>k</mi> <mo>=</mo> <mn>2</mn> </mrow> </math></EquationSource> </InlineEquation>, then we show that <i>M</i> is contained in a neighbourhood of controlled width of an isometrically embedded 1-dimensional sub-manifold. From this, we deduce several metric and topological consequences: <i>M</i> has at most linear volume growth and at most two ends, it has bounded 1-Urysohn width, the first Betti number of <i>M</i> is bounded above by 1, and there is precise information on elements of infinite order in <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(\pi _1(M)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>π</mi> <mn>1</mn> </msub> <mrow> <mo stretchy="false">(</mo> <mi>M</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation>. If <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\((M^n,g)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <msup> <mi>M</mi> <mi>n</mi> </msup> <mo>,</mo> <mi>g</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> is a Riemannian manifold satisfying such bounds for <InlineEquation ID="IEq7"> <EquationSource Format="TEX">\(k\ge 2\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>k</mi> <mo>≥</mo> <mn>2</mn> </mrow> </math></EquationSource> </InlineEquation>, then we show that <i>M</i> has at most <InlineEquation ID="IEq8"> <EquationSource Format="TEX">\((k-1)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <mi>k</mi> <mo>-</mo> <mn>1</mn> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation>-dimensional behavior at large scales. If <InlineEquation ID="IEq9"> <EquationSource Format="TEX">\(k=n=\textrm{dim}(M)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>k</mi> <mo>=</mo> <mi>n</mi> <mo>=</mo> <mtext>dim</mtext> <mo stretchy="false">(</mo> <mi>M</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation>, so that the integral lower bound is on the scalar curvature, assuming in addition that the <InlineEquation ID="IEq10"> <EquationSource Format="TEX">\((n-2)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <mi>n</mi> <mo>-</mo> <mn>2</mn> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation>-Ricci curvature is non-negative, we prove that the dimension drop at large scales improves to <InlineEquation ID="IEq11"> <EquationSource Format="TEX">\(n-2\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>n</mi> <mo>-</mo> <mn>2</mn> </mrow> </math></EquationSource> </InlineEquation>. From the above results we deduce topological restrictions, such as upper bounds on the first Betti number.</p>

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On manifolds with almost non-negative Ricci curvature and integrally-positive \(k^{th}\)-scalar curvature

  • Alessandro Cucinotta,
  • Andrea Mondino

摘要

We consider manifolds with almost non-negative Ricci curvature and strictly positive integral lower bounds on the sum of the lowest k eigenvalues of the Ricci tensor. If \((M^n,g)\) ( M n , g ) is a Riemannian manifold satisfying such curvature bounds for \(k=2\) k = 2 , then we show that M is contained in a neighbourhood of controlled width of an isometrically embedded 1-dimensional sub-manifold. From this, we deduce several metric and topological consequences: M has at most linear volume growth and at most two ends, it has bounded 1-Urysohn width, the first Betti number of M is bounded above by 1, and there is precise information on elements of infinite order in \(\pi _1(M)\) π 1 ( M ) . If \((M^n,g)\) ( M n , g ) is a Riemannian manifold satisfying such bounds for \(k\ge 2\) k 2 , then we show that M has at most \((k-1)\) ( k - 1 ) -dimensional behavior at large scales. If \(k=n=\textrm{dim}(M)\) k = n = dim ( M ) , so that the integral lower bound is on the scalar curvature, assuming in addition that the \((n-2)\) ( n - 2 ) -Ricci curvature is non-negative, we prove that the dimension drop at large scales improves to \(n-2\) n - 2 . From the above results we deduce topological restrictions, such as upper bounds on the first Betti number.