<p>We investigate a one-parameter deformation of the Ricci flow arising from the Lagrangian <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(L = f(R) = R^{1 + \varepsilon }\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>L</mi> <mo>=</mo> <mi>f</mi> <mrow> <mo stretchy="false">(</mo> <mi>R</mi> <mo stretchy="false">)</mo> </mrow> <mo>=</mo> <msup> <mi>R</mi> <mrow> <mn>1</mn> <mo>+</mo> <mi>ε</mi> </mrow> </msup> </mrow> </math></EquationSource> </InlineEquation> where <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(\varepsilon\)</EquationSource> <EquationSource Format="MATHML"><math> <mi>ε</mi> </math></EquationSource> </InlineEquation> is a small real parameter. Varying this action with respect to the metric, yields a fourth-order geometric flow, that reduces to the Ricci flow as <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(\varepsilon \to 0\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>ε</mi> <mo stretchy="false">→</mo> <mn>0</mn> </mrow> </math></EquationSource> </InlineEquation>. The corresponding evolution equation is: <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(\partial_{t} g_{ij} = - 2{\mathcal{E}}_{ij} = - 2\left( {1 + \varepsilon } \right)R^{\varepsilon } R_{ij} + g_{ij} R^{1 + \varepsilon } + 2\left( {1 + \varepsilon } \right)\left( {\nabla_{i} \nabla_{j} - g_{ij} {\square }} \right)R^{\varepsilon }\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>∂</mi> <mi>t</mi> </msub> <msub> <mi>g</mi> <mrow> <mi mathvariant="italic">ij</mi> </mrow> </msub> <mo>=</mo> <mo>-</mo> <mn>2</mn> <msub> <mi mathvariant="script">E</mi> <mrow> <mi mathvariant="italic">ij</mi> </mrow> </msub> <mo>=</mo> <mo>-</mo> <mn>2</mn> <mfenced close=")" open="("> <mrow> <mn>1</mn> <mo>+</mo> <mi>ε</mi> </mrow> </mfenced> <msup> <mi>R</mi> <mi>ε</mi> </msup> <msub> <mi>R</mi> <mrow> <mi mathvariant="italic">ij</mi> </mrow> </msub> <mo>+</mo> <msub> <mi>g</mi> <mrow> <mi mathvariant="italic">ij</mi> </mrow> </msub> <msup> <mi>R</mi> <mrow> <mn>1</mn> <mo>+</mo> <mi>ε</mi> </mrow> </msup> <mo>+</mo> <mn>2</mn> <mfenced close=")" open="("> <mrow> <mn>1</mn> <mo>+</mo> <mi>ε</mi> </mrow> </mfenced> <mfenced close=")" open="("> <mrow> <msub> <mi mathvariant="normal">∇</mi> <mi>i</mi> </msub> <msub> <mi mathvariant="normal">∇</mi> <mi>j</mi> </msub> <mo>-</mo> <msub> <mi>g</mi> <mrow> <mi mathvariant="italic">ij</mi> </mrow> </msub> <mo>□</mo> </mrow> </mfenced> <msup> <mi>R</mi> <mi>ε</mi> </msup> </mrow> </math></EquationSource> </InlineEquation>. We derive the evolution of the scalar curvature, its small—expansion, and the associated fourth-order corrections to the standard Ricci flow. Linear analysis shows that for <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(\varepsilon &gt; 0\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>ε</mi> <mo>&gt;</mo> <mn>0</mn> </mrow> </math></EquationSource> </InlineEquation>, the flow exhibits higher-order diffusion through bi-Laplacian-type terms, modifying the stability of Einstein metrics. Soliton (self-similar) solutions satisfy a generalized equation involving the Hessian of a potential <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\(f\)</EquationSource> <EquationSource Format="MATHML"><math> <mi>f</mi> </math></EquationSource> </InlineEquation> and the curvature scalar <InlineEquation ID="IEq7"> <EquationSource Format="TEX">\(R^{\varepsilon }\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mi>R</mi> <mi>ε</mi> </msup> </math></EquationSource> </InlineEquation>. For constant-curvature (Einstein) metrics, we find explicit solitons with scaling parameter <InlineEquation ID="IEq8"> <EquationSource Format="TEX">\(\sigma = - \frac{1 + n}{\varepsilon } - \frac{1}{2}R^{1 + \varepsilon } ,\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>σ</mi> <mo>=</mo> <mo>-</mo> <mfrac> <mrow> <mn>1</mn> <mo>+</mo> <mi>n</mi> </mrow> <mi>ε</mi> </mfrac> <mo>-</mo> <mfrac> <mn>1</mn> <mn>2</mn> </mfrac> <msup> <mi>R</mi> <mrow> <mn>1</mn> <mo>+</mo> <mi>ε</mi> </mrow> </msup> <mo>,</mo> </mrow> </math></EquationSource> </InlineEquation> whose sign determines whether the soliton is shrinking, steady, or expanding. We also present a generalized formulation of the Ricci flow derived from a deformed Perelman functional: <InlineEquation ID="IEq9"> <EquationSource Format="TEX">\({\mathbf{\mathcal{F}}}_{\varepsilon } [f,g_{ij} ]: = \int\limits_{M} {e^{ - f} \left( {\left| {\nabla f} \right|^{2} + R} \right)^{1 + \varepsilon } dV} ,\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi mathvariant="script">F</mi> <mi>ε</mi> </msub> <mrow> <mo stretchy="false">[</mo> <mi>f</mi> <mo>,</mo> <msub> <mi>g</mi> <mrow> <mi mathvariant="italic">ij</mi> </mrow> </msub> <mo stretchy="false">]</mo> </mrow> <mo>:</mo> <mo>=</mo> <munder> <mo movablelimits="false">∫</mo> <mi>M</mi> </munder> <mrow> <msup> <mi>e</mi> <mrow> <mo>-</mo> <mi>f</mi> </mrow> </msup> <msup> <mfenced close=")" open="("> <mrow> <msup> <mfenced close="|" open="|"> <mrow> <mi mathvariant="normal">∇</mi> <mi>f</mi> </mrow> </mfenced> <mn>2</mn> </msup> <mo>+</mo> <mi>R</mi> </mrow> </mfenced> <mrow> <mn>1</mn> <mo>+</mo> <mi>ε</mi> </mrow> </msup> <mi>d</mi> <mi>V</mi> </mrow> <mo>,</mo> </mrow> </math></EquationSource> </InlineEquation> where <InlineEquation ID="IEq10"> <EquationSource Format="TEX">\(\varepsilon\)</EquationSource> <EquationSource Format="MATHML"><math> <mi>ε</mi> </math></EquationSource> </InlineEquation> is a real deformation parameter. By varying this functional with respect to the metric <InlineEquation ID="IEq11"> <EquationSource Format="TEX">\(g_{ij}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>g</mi> <mrow> <mi mathvariant="italic">ij</mi> </mrow> </msub> </math></EquationSource> </InlineEquation> and scalar field <InlineEquation ID="IEq12"> <EquationSource Format="TEX">\(f\)</EquationSource> <EquationSource Format="MATHML"><math> <mi>f</mi> </math></EquationSource> </InlineEquation> we obtain a modified Ricci flow system in which the classical Perelman equations are rescaled by the curvature–gradient factor <InlineEquation ID="IEq13"> <EquationSource Format="TEX">\((\left| {\nabla f} \right|^{2} + R)^{\varepsilon }\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mrow> <mo stretchy="false">(</mo> <msup> <mfenced close="|" open="|"> <mrow> <mi mathvariant="normal">∇</mi> <mi>f</mi> </mrow> </mfenced> <mn>2</mn> </msup> <mo>+</mo> <mi>R</mi> <mo stretchy="false">)</mo> </mrow> <mi>ε</mi> </msup> </math></EquationSource> </InlineEquation> and supplemented by additional higher-order coupling terms involving derivatives of <InlineEquation ID="IEq14"> <EquationSource Format="TEX">\(L = \left| {\nabla f} \right|^{2} + R\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>L</mi> <mo>=</mo> <msup> <mfenced close="|" open="|"> <mrow> <mi mathvariant="normal">∇</mi> <mi>f</mi> </mrow> </mfenced> <mn>2</mn> </msup> <mo>+</mo> <mi>R</mi> </mrow> </math></EquationSource> </InlineEquation>. The resulting evolution equations preserve the parabolic nature of the Ricci flow while introducing nontrivial corrections that affect entropy and monotonicity properties. A small-<InlineEquation ID="IEq15"> <EquationSource Format="TEX">\(\varepsilon\)</EquationSource> <EquationSource Format="MATHML"><math> <mi>ε</mi> </math></EquationSource> </InlineEquation> expansion yields explicit first-order corrections of the form <InlineEquation ID="IEq16"> <EquationSource Format="TEX">\(L\ln L\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>L</mi> <mo>ln</mo> <mi>L</mi> </mrow> </math></EquationSource> </InlineEquation>, revealing the mechanism through which Perelman’s entropy monotonicity is perturbed. This deformation provides a controlled one-parameter extension of Ricci flow dynamics, offering a framework for exploring generalized geometric flows, entropy production, and stability analysis in Riemannian geometry. We also study a generalization of the Ricci flow driven by a combined functional incorporating the <InlineEquation ID="IEq17"> <EquationSource Format="TEX">\(L^{1 + \varepsilon (t)}\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mi>L</mi> <mrow> <mn>1</mn> <mo>+</mo> <mi>ε</mi> <mo stretchy="false">(</mo> <mi>t</mi> <mo stretchy="false">)</mo> </mrow> </msup> </math></EquationSource> </InlineEquation> norm of the curvature tensor, where <InlineEquation ID="IEq18"> <EquationSource Format="TEX">\(\varepsilon (t)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>ε</mi> <mo stretchy="false">(</mo> <mi>t</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> is a time-dependent exponent. This formulation leads to a nonautonomous geometric flow in which the curvature regions are weighted dynamically, and introduces a mixed 2nd- and 4th-order structure in the evolution equations. Of particular interest are soliton solutions whose existence and stability are strongly influenced by the temporal behavior of the Lagrangian exponent <InlineEquation ID="IEq19"> <EquationSource Format="TEX">\(1 + \varepsilon (t)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mn>1</mn> <mo>+</mo> <mi>ε</mi> <mo stretchy="false">(</mo> <mi>t</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation>. The time-dependence affects both the gradient structure of the functional and the balance between Ricci diffusion and curvature concentration, thereby playing a central role in determining whether self-similar or perturbative solitons can arise. Our analysis highlights the sensitivity of soliton formation to variations in <InlineEquation ID="IEq20"> <EquationSource Format="TEX">\(\varepsilon (t)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>ε</mi> <mo stretchy="false">(</mo> <mi>t</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation>, offering a framework to study new families of generalized solitons and their geometric properties. Two conjectures have been also proposed.</p>

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Generalized gradient flows of curvature: a power-law Ricci flow framework

  • Rami Ahmad El-Nabulsi

摘要

We investigate a one-parameter deformation of the Ricci flow arising from the Lagrangian \(L = f(R) = R^{1 + \varepsilon }\) L = f ( R ) = R 1 + ε where \(\varepsilon\) ε is a small real parameter. Varying this action with respect to the metric, yields a fourth-order geometric flow, that reduces to the Ricci flow as \(\varepsilon \to 0\) ε 0 . The corresponding evolution equation is: \(\partial_{t} g_{ij} = - 2{\mathcal{E}}_{ij} = - 2\left( {1 + \varepsilon } \right)R^{\varepsilon } R_{ij} + g_{ij} R^{1 + \varepsilon } + 2\left( {1 + \varepsilon } \right)\left( {\nabla_{i} \nabla_{j} - g_{ij} {\square }} \right)R^{\varepsilon }\) t g ij = - 2 E ij = - 2 1 + ε R ε R ij + g ij R 1 + ε + 2 1 + ε i j - g ij R ε . We derive the evolution of the scalar curvature, its small—expansion, and the associated fourth-order corrections to the standard Ricci flow. Linear analysis shows that for \(\varepsilon > 0\) ε > 0 , the flow exhibits higher-order diffusion through bi-Laplacian-type terms, modifying the stability of Einstein metrics. Soliton (self-similar) solutions satisfy a generalized equation involving the Hessian of a potential \(f\) f and the curvature scalar \(R^{\varepsilon }\) R ε . For constant-curvature (Einstein) metrics, we find explicit solitons with scaling parameter \(\sigma = - \frac{1 + n}{\varepsilon } - \frac{1}{2}R^{1 + \varepsilon } ,\) σ = - 1 + n ε - 1 2 R 1 + ε , whose sign determines whether the soliton is shrinking, steady, or expanding. We also present a generalized formulation of the Ricci flow derived from a deformed Perelman functional: \({\mathbf{\mathcal{F}}}_{\varepsilon } [f,g_{ij} ]: = \int\limits_{M} {e^{ - f} \left( {\left| {\nabla f} \right|^{2} + R} \right)^{1 + \varepsilon } dV} ,\) F ε [ f , g ij ] : = M e - f f 2 + R 1 + ε d V , where \(\varepsilon\) ε is a real deformation parameter. By varying this functional with respect to the metric \(g_{ij}\) g ij and scalar field \(f\) f we obtain a modified Ricci flow system in which the classical Perelman equations are rescaled by the curvature–gradient factor \((\left| {\nabla f} \right|^{2} + R)^{\varepsilon }\) ( f 2 + R ) ε and supplemented by additional higher-order coupling terms involving derivatives of \(L = \left| {\nabla f} \right|^{2} + R\) L = f 2 + R . The resulting evolution equations preserve the parabolic nature of the Ricci flow while introducing nontrivial corrections that affect entropy and monotonicity properties. A small- \(\varepsilon\) ε expansion yields explicit first-order corrections of the form \(L\ln L\) L ln L , revealing the mechanism through which Perelman’s entropy monotonicity is perturbed. This deformation provides a controlled one-parameter extension of Ricci flow dynamics, offering a framework for exploring generalized geometric flows, entropy production, and stability analysis in Riemannian geometry. We also study a generalization of the Ricci flow driven by a combined functional incorporating the \(L^{1 + \varepsilon (t)}\) L 1 + ε ( t ) norm of the curvature tensor, where \(\varepsilon (t)\) ε ( t ) is a time-dependent exponent. This formulation leads to a nonautonomous geometric flow in which the curvature regions are weighted dynamically, and introduces a mixed 2nd- and 4th-order structure in the evolution equations. Of particular interest are soliton solutions whose existence and stability are strongly influenced by the temporal behavior of the Lagrangian exponent \(1 + \varepsilon (t)\) 1 + ε ( t ) . The time-dependence affects both the gradient structure of the functional and the balance between Ricci diffusion and curvature concentration, thereby playing a central role in determining whether self-similar or perturbative solitons can arise. Our analysis highlights the sensitivity of soliton formation to variations in \(\varepsilon (t)\) ε ( t ) , offering a framework to study new families of generalized solitons and their geometric properties. Two conjectures have been also proposed.