<p>Let <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11118_2025_10214_Article_IEq1.gif" Format="GIF" Height="17" Rendition="HTML" Resolution="72" Type="Linedraw" Width="78" /> </InlineMediaObject> <EquationSource Format="TEX">\(\Omega ^+\subset {\mathbb R}^{n+1}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msup> <mi mathvariant="normal">Ω</mi> <mo>+</mo> </msup> <mo>⊂</mo> <msup> <mrow> <mi mathvariant="double-struck">R</mi> </mrow> <mrow> <mi>n</mi> <mo>+</mo> <mn>1</mn> </mrow> </msup> </mrow> </math></EquationSource> </InlineEquation> be a vanishing Reifenberg flat domain such that <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11118_2025_10214_Article_IEq2.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="22" /> </InlineMediaObject> <EquationSource Format="TEX">\(\Omega ^+\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mi mathvariant="normal">Ω</mi> <mo>+</mo> </msup> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11118_2025_10214_Article_IEq3.gif" Format="GIF" Height="21" Rendition="HTML" Resolution="72" Type="Linedraw" Width="115" /> </InlineMediaObject> <EquationSource Format="TEX">\(\Omega ^-={\mathbb R}^{n+1}\setminus \overline{\Omega ^+}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msup> <mi mathvariant="normal">Ω</mi> <mo>-</mo> </msup> <mo>=</mo> <msup> <mrow> <mi mathvariant="double-struck">R</mi> </mrow> <mrow> <mi>n</mi> <mo>+</mo> <mn>1</mn> </mrow> </msup> <mo lspace="0.15em" rspace="0.15em" stretchy="false">\</mo> <mover> <msup> <mi mathvariant="normal">Ω</mi> <mo>+</mo> </msup> <mo>¯</mo> </mover> </mrow> </math></EquationSource> </InlineEquation> have joint big pieces of chord-arc subdomains and such that the outer unit normal to <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11118_2025_10214_Article_IEq4.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="32" /> </InlineMediaObject> <EquationSource Format="TEX">\(\partial \Omega ^+\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>∂</mi> <msup> <mi mathvariant="normal">Ω</mi> <mo>+</mo> </msup> </mrow> </math></EquationSource> </InlineEquation> belongs to <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11118_2025_10214_Article_IEq5.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="74" /> </InlineMediaObject> <EquationSource Format="TEX">\({{\text {VMO}}}(\omega ^+)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mtext>VMO</mtext> <mo stretchy="false">(</mo> <msup> <mi>ω</mi> <mo>+</mo> </msup> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation>, where <InlineEquation ID="IEq6"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11118_2025_10214_Article_IEq6.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="24" /> </InlineMediaObject> <EquationSource Format="TEX">\(\omega ^\pm \)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mi>ω</mi> <mo>±</mo> </msup> </math></EquationSource> </InlineEquation> is the harmonic measure in <InlineEquation ID="IEq7"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11118_2025_10214_Article_IEq7.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="24" /> </InlineMediaObject> <EquationSource Format="TEX">\(\Omega ^\pm \)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mi mathvariant="normal">Ω</mi> <mo>±</mo> </msup> </math></EquationSource> </InlineEquation>. Up to now it was an open question if these conditions imply that <InlineEquation ID="IEq8"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11118_2025_10214_Article_IEq8.gif" Format="GIF" Height="39" Rendition="HTML" Resolution="72" Type="Linedraw" Width="150" /> </InlineMediaObject> <EquationSource Format="TEX">\(\log \dfrac{d\omega ^-}{d\omega ^+} \in {{\text {VMO}}}(\omega ^+)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo>log</mo> <mstyle displaystyle="true" scriptlevel="0"> <mfrac> <mrow> <mi>d</mi> <msup> <mi>ω</mi> <mo>-</mo> </msup> </mrow> <mrow> <mi>d</mi> <msup> <mi>ω</mi> <mo>+</mo> </msup> </mrow> </mfrac> </mstyle> <mo>∈</mo> <mtext>VMO</mtext> <mrow> <mo stretchy="false">(</mo> <msup> <mi>ω</mi> <mo>+</mo> </msup> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation>. In this paper we answer this question in the negative by constructing an appropriate counterexample in <InlineEquation ID="IEq9"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11118_2025_10214_Article_IEq9.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="18" /> </InlineMediaObject> <EquationSource Format="TEX">\({\mathbb R}^2\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mrow> <mi mathvariant="double-struck">R</mi> </mrow> <mn>2</mn> </msup> </math></EquationSource> </InlineEquation>, with the additional property that the outer unit normal to <InlineEquation ID="IEq10"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11118_2025_10214_Article_IEq4.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="32" /> </InlineMediaObject> <EquationSource Format="TEX">\(\partial \Omega ^+\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>∂</mi> <msup> <mi mathvariant="normal">Ω</mi> <mo>+</mo> </msup> </mrow> </math></EquationSource> </InlineEquation> is constant <InlineEquation ID="IEq11"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11118_2025_10214_Article_IEq11.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="22" /> </InlineMediaObject> <EquationSource Format="TEX">\(\omega ^+\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mi>ω</mi> <mo>+</mo> </msup> </math></EquationSource> </InlineEquation>-a.e. in <InlineEquation ID="IEq12"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11118_2025_10214_Article_IEq12.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="38" /> </InlineMediaObject> <EquationSource Format="TEX">\(\partial \Omega ^+.\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>∂</mi> <msup> <mi mathvariant="normal">Ω</mi> <mo>+</mo> </msup> <mo>.</mo> </mrow> </math></EquationSource> </InlineEquation></p>

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A Counterexample Regarding a Two-phase Problem for Harmonic Measure in VMO

  • Xavier Tolsa

摘要

Let \(\Omega ^+\subset {\mathbb R}^{n+1}\) Ω + R n + 1 be a vanishing Reifenberg flat domain such that \(\Omega ^+\) Ω + and \(\Omega ^-={\mathbb R}^{n+1}\setminus \overline{\Omega ^+}\) Ω - = R n + 1 \ Ω + ¯ have joint big pieces of chord-arc subdomains and such that the outer unit normal to \(\partial \Omega ^+\) Ω + belongs to \({{\text {VMO}}}(\omega ^+)\) VMO ( ω + ) , where \(\omega ^\pm \) ω ± is the harmonic measure in \(\Omega ^\pm \) Ω ± . Up to now it was an open question if these conditions imply that \(\log \dfrac{d\omega ^-}{d\omega ^+} \in {{\text {VMO}}}(\omega ^+)\) log d ω - d ω + VMO ( ω + ) . In this paper we answer this question in the negative by constructing an appropriate counterexample in \({\mathbb R}^2\) R 2 , with the additional property that the outer unit normal to \(\partial \Omega ^+\) Ω + is constant \(\omega ^+\) ω + -a.e. in \(\partial \Omega ^+.\) Ω + .