<p>We study the weighted differential operators <Equation ID="Equ23"> <MediaObject> <ImageObject Color="BlackWhite" FileRef="40840_2025_1965_Article_Equ23.gif" Format="GIF" Height="39" Rendition="HTML" Resolution="72" Type="Linedraw" Width="391" /> </MediaObject> <EquationSource Format="TEX">\(\begin{aligned} \Delta _\alpha = (1-|x|^2)\Bigl (\frac{1-|x|^2}{4}\Delta + \frac{\alpha }{2}\,x\cdot \nabla + \frac{\alpha (n-2-\alpha )}{4}\Bigr ) \end{aligned}\)</EquationSource> <EquationSource Format="MATHML"><math display="block"> <mrow> <mtable> <mtr> <mtd columnalign="right"> <mrow> <msub> <mi mathvariant="normal">Δ</mi> <mi>α</mi> </msub> <mo>=</mo> <msup> <mrow> <mo stretchy="false">(</mo> <mn>1</mn> <mo>-</mo> <mo stretchy="false">|</mo> <mi>x</mi> <mo stretchy="false">|</mo> </mrow> <mn>2</mn> </msup> <mrow> <mo stretchy="false">)</mo> <mrow> <mo maxsize="1.623em" minsize="1.623em" stretchy="true">(</mo> </mrow> </mrow> <mfrac> <mrow> <mn>1</mn> <mo>-</mo> <msup> <mrow> <mo stretchy="false">|</mo> <mi>x</mi> <mo stretchy="false">|</mo> </mrow> <mn>2</mn> </msup> </mrow> <mn>4</mn> </mfrac> <mi mathvariant="normal">Δ</mi> <mo>+</mo> <mfrac> <mi>α</mi> <mn>2</mn> </mfrac> <mspace width="0.166667em" /> <mi>x</mi> <mo>·</mo> <mi mathvariant="normal">∇</mi> <mo>+</mo> <mfrac> <mrow> <mi>α</mi> <mo stretchy="false">(</mo> <mi>n</mi> <mo>-</mo> <mn>2</mn> <mo>-</mo> <mi>α</mi> <mo stretchy="false">)</mo> </mrow> <mn>4</mn> </mfrac> <mrow> <mo maxsize="1.623em" minsize="1.623em" stretchy="true">)</mo> </mrow> </mrow> </mtd> </mtr> </mtable> </mrow> </math></EquationSource> </Equation>on the unit ball <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40840_2025_1965_Article_IEq1.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="61" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mathbb {B}^n\subset \mathbb {R}^n\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msup> <mrow> <mi mathvariant="double-struck">B</mi> </mrow> <mi>n</mi> </msup> <mo>⊂</mo> <msup> <mrow> <mi mathvariant="double-struck">R</mi> </mrow> <mi>n</mi> </msup> </mrow> </math></EquationSource> </InlineEquation>. These operators generalize the classical Laplacian and, for certain values of <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40840_2025_1965_Article_IEq2.gif" Format="GIF" Height="10" Rendition="HTML" Resolution="72" Type="Linedraw" Width="14" /> </InlineMediaObject> <EquationSource Format="TEX">\(\alpha \)</EquationSource> <EquationSource Format="MATHML"><math> <mi>α</mi> </math></EquationSource> </InlineEquation>, recover the Laplace–Beltrami operator. Our main contributions are twofold. First, we derive sharp pointwise estimates for <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40840_2025_1965_Article_IEq2.gif" Format="GIF" Height="10" Rendition="HTML" Resolution="72" Type="Linedraw" Width="14" /> </InlineMediaObject> <EquationSource Format="TEX">\(\alpha \)</EquationSource> <EquationSource Format="MATHML"><math> <mi>α</mi> </math></EquationSource> </InlineEquation>-harmonic functions (solutions to <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40840_2025_1965_Article_IEq4.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="62" /> </InlineMediaObject> <EquationSource Format="TEX">\(\Delta _\alpha u=0\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi mathvariant="normal">Δ</mi> <mi>α</mi> </msub> <mi>u</mi> <mo>=</mo> <mn>0</mn> </mrow> </math></EquationSource> </InlineEquation>) using a Poisson-type integral representation. This extends prior results on harmonic, hyperbolic harmonic functions, and weighted planar harmonic functions to higher dimensions. Second, we characterize radial eigenfunctions of <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40840_2025_1965_Article_IEq5.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="24" /> </InlineMediaObject> <EquationSource Format="TEX">\(\Delta _\alpha \)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi mathvariant="normal">Δ</mi> <mi>α</mi> </msub> </math></EquationSource> </InlineEquation> in terms of Gauss hypergeometric functions, showing an explicit relationship between radial eigenfunctions and the powers of the generalized <InlineEquation ID="IEq6"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40840_2025_1965_Article_IEq2.gif" Format="GIF" Height="10" Rendition="HTML" Resolution="72" Type="Linedraw" Width="14" /> </InlineMediaObject> <EquationSource Format="TEX">\(\alpha \)</EquationSource> <EquationSource Format="MATHML"><math> <mi>α</mi> </math></EquationSource> </InlineEquation>-Poisson kernel. This unified framework links Euclidean and hyperbolic harmonic analysis.</p>

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Growth of Generalized Harmonic Functions and Radial Eigenfunctions

  • Adel Khalfallah

摘要

We study the weighted differential operators \(\begin{aligned} \Delta _\alpha = (1-|x|^2)\Bigl (\frac{1-|x|^2}{4}\Delta + \frac{\alpha }{2}\,x\cdot \nabla + \frac{\alpha (n-2-\alpha )}{4}\Bigr ) \end{aligned}\) Δ α = ( 1 - | x | 2 ) ( 1 - | x | 2 4 Δ + α 2 x · + α ( n - 2 - α ) 4 ) on the unit ball \(\mathbb {B}^n\subset \mathbb {R}^n\) B n R n . These operators generalize the classical Laplacian and, for certain values of \(\alpha \) α , recover the Laplace–Beltrami operator. Our main contributions are twofold. First, we derive sharp pointwise estimates for \(\alpha \) α -harmonic functions (solutions to \(\Delta _\alpha u=0\) Δ α u = 0 ) using a Poisson-type integral representation. This extends prior results on harmonic, hyperbolic harmonic functions, and weighted planar harmonic functions to higher dimensions. Second, we characterize radial eigenfunctions of \(\Delta _\alpha \) Δ α in terms of Gauss hypergeometric functions, showing an explicit relationship between radial eigenfunctions and the powers of the generalized \(\alpha \) α -Poisson kernel. This unified framework links Euclidean and hyperbolic harmonic analysis.