<p>The supersaturation problem for a given graph <i>F</i> asks for the minimum number <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="493_2025_143_Article_IEq1.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="59" /> </InlineMediaObject> <EquationSource Format="TEX">\(h_F(n,q)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>h</mi> <mi>F</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>n</mi> <mo>,</mo> <mi>q</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> of copies of <i>F</i> in an <i>n</i>-vertex graph with <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="493_2025_143_Article_IEq2.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="90" /> </InlineMediaObject> <EquationSource Format="TEX">\(\textrm{ex}(n,F)+q\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mtext>ex</mtext> <mo stretchy="false">(</mo> <mi>n</mi> <mo>,</mo> <mi>F</mi> <mo stretchy="false">)</mo> <mo>+</mo> <mi>q</mi> </mrow> </math></EquationSource> </InlineEquation> edges. Subsequent works by Rademacher, Erdős, and Lovász and Simonovits determine the optimal range of <i>q</i> (which is linear in <i>n</i>) for cliques <i>F</i> such that <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="493_2025_143_Article_IEq3.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="59" /> </InlineMediaObject> <EquationSource Format="TEX">\(h_F(n,q)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>h</mi> <mi>F</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>n</mi> <mo>,</mo> <mi>q</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> equals the minimum number <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="493_2025_143_Article_IEq4.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="55" /> </InlineMediaObject> <EquationSource Format="TEX">\(t_F(n,q)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>t</mi> <mi>F</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>n</mi> <mo>,</mo> <mi>q</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> of copies of <i>F</i> obtained from a maximum <i>F</i>-free <i>n</i>-vertex graph by adding <i>q</i> new edges. A breakthrough result of Mubayi extends this line of research from cliques to color-critical graphs <i>F</i>, and this was further strengthened by Pikhurko and Yilma who established the equality <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="493_2025_143_Article_IEq5.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="135" /> </InlineMediaObject> <EquationSource Format="TEX">\(h_F(n,q)=t_F(n,q)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>h</mi> <mi>F</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>n</mi> <mo>,</mo> <mi>q</mi> <mo stretchy="false">)</mo> </mrow> <mo>=</mo> <msub> <mi>t</mi> <mi>F</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>n</mi> <mo>,</mo> <mi>q</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> for <InlineEquation ID="IEq6"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="493_2025_143_Article_IEq6.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="92" /> </InlineMediaObject> <EquationSource Format="TEX">\(1\le q\le \epsilon _F n\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mn>1</mn> <mo>≤</mo> <mi>q</mi> <mo>≤</mo> <msub> <mi>ϵ</mi> <mi>F</mi> </msub> <mi>n</mi> </mrow> </math></EquationSource> </InlineEquation> and sufficiently large <i>n</i>. In this paper, we present several results on the supersaturation problem that extend beyond the existing framework. Firstly, we explicitly construct infinitely many graphs <i>F</i> with restricted properties for which <InlineEquation ID="IEq7"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="493_2025_143_Article_IEq7.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="156" /> </InlineMediaObject> <EquationSource Format="TEX">\(h_F(n,q)&lt;q\cdot t_F(n,1)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>h</mi> <mi>F</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>n</mi> <mo>,</mo> <mi>q</mi> <mo stretchy="false">)</mo> </mrow> <mo>&lt;</mo> <mi>q</mi> <mo>·</mo> <msub> <mi>t</mi> <mi>F</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>n</mi> <mo>,</mo> <mn>1</mn> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> holds when <InlineEquation ID="IEq8"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="493_2025_143_Article_IEq8.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="78" /> </InlineMediaObject> <EquationSource Format="TEX">\(n\gg q\ge 4\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>n</mi> <mo>≫</mo> <mi>q</mi> <mo>≥</mo> <mn>4</mn> </mrow> </math></EquationSource> </InlineEquation>, thus refuting a conjecture of Mubayi. Secondly, we extend the result of Pikhurko–Yilma by showing the equality <InlineEquation ID="IEq9"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="493_2025_143_Article_IEq9.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="135" /> </InlineMediaObject> <EquationSource Format="TEX">\(h_F(n,q)=t_F(n,q)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>h</mi> <mi>F</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>n</mi> <mo>,</mo> <mi>q</mi> <mo stretchy="false">)</mo> </mrow> <mo>=</mo> <msub> <mi>t</mi> <mi>F</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>n</mi> <mo>,</mo> <mi>q</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> in the range <InlineEquation ID="IEq10"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="493_2025_143_Article_IEq10.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="92" /> </InlineMediaObject> <EquationSource Format="TEX">\(1\le q\le \epsilon _F n\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mn>1</mn> <mo>≤</mo> <mi>q</mi> <mo>≤</mo> <msub> <mi>ϵ</mi> <mi>F</mi> </msub> <mi>n</mi> </mrow> </math></EquationSource> </InlineEquation> for any member <i>F</i> in a diverse and abundant graph family (which includes color-critical graphs, disjoint unions of cliques <InlineEquation ID="IEq11"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="493_2025_143_Article_IEq11.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="23" /> </InlineMediaObject> <EquationSource Format="TEX">\(K_r\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>K</mi> <mi>r</mi> </msub> </math></EquationSource> </InlineEquation>, and the Petersen graph). Lastly, we prove the existence of a graph <i>F</i> for any positive integer <i>s</i> such that <InlineEquation ID="IEq12"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="493_2025_143_Article_IEq12.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="135" /> </InlineMediaObject> <EquationSource Format="TEX">\(h_F(n,q)=t_F(n,q)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>h</mi> <mi>F</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>n</mi> <mo>,</mo> <mi>q</mi> <mo stretchy="false">)</mo> </mrow> <mo>=</mo> <msub> <mi>t</mi> <mi>F</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>n</mi> <mo>,</mo> <mi>q</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> holds when <InlineEquation ID="IEq13"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="493_2025_143_Article_IEq13.gif" Format="GIF" Height="20" Rendition="HTML" Resolution="72" Type="Linedraw" Width="124" /> </InlineMediaObject> <EquationSource Format="TEX">\(1\le q\le \epsilon _F n^{1-1/s}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mn>1</mn> <mo>≤</mo> <mi>q</mi> <mo>≤</mo> <msub> <mi>ϵ</mi> <mi>F</mi> </msub> <msup> <mi>n</mi> <mrow> <mn>1</mn> <mo>-</mo> <mn>1</mn> <mo stretchy="false">/</mo> <mi>s</mi> </mrow> </msup> </mrow> </math></EquationSource> </InlineEquation>, and <InlineEquation ID="IEq14"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="493_2025_143_Article_IEq14.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="135" /> </InlineMediaObject> <EquationSource Format="TEX">\(h_F(n,q)&lt;t_F(n,q)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>h</mi> <mi>F</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>n</mi> <mo>,</mo> <mi>q</mi> <mo stretchy="false">)</mo> </mrow> <mo>&lt;</mo> <msub> <mi>t</mi> <mi>F</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>n</mi> <mo>,</mo> <mi>q</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> when <InlineEquation ID="IEq15"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="493_2025_143_Article_IEq15.gif" Format="GIF" Height="21" Rendition="HTML" Resolution="72" Type="Linedraw" Width="152" /> </InlineMediaObject> <EquationSource Format="TEX">\(n^{1-1/s}/\epsilon _F\le q\le \epsilon _F n\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msup> <mi>n</mi> <mrow> <mn>1</mn> <mo>-</mo> <mn>1</mn> <mo stretchy="false">/</mo> <mi>s</mi> </mrow> </msup> <mo stretchy="false">/</mo> <msub> <mi>ϵ</mi> <mi>F</mi> </msub> <mo>≤</mo> <mi>q</mi> <mo>≤</mo> <msub> <mi>ϵ</mi> <mi>F</mi> </msub> <mi>n</mi> </mrow> </math></EquationSource> </InlineEquation>, indicating that <InlineEquation ID="IEq16"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="493_2025_143_Article_IEq16.gif" Format="GIF" Height="21" Rendition="HTML" Resolution="72" Type="Linedraw" Width="100" /> </InlineMediaObject> <EquationSource Format="TEX">\(q=\Theta (n^{1-1/s})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>q</mi> <mo>=</mo> <mi mathvariant="normal">Θ</mi> <mo stretchy="false">(</mo> <msup> <mi>n</mi> <mrow> <mn>1</mn> <mo>-</mo> <mn>1</mn> <mo stretchy="false">/</mo> <mi>s</mi> </mrow> </msup> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> serves as the threshold for the equality <InlineEquation ID="IEq17"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="493_2025_143_Article_IEq17.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="135" /> </InlineMediaObject> <EquationSource Format="TEX">\(h_F(n,q)=t_F(n,q)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>h</mi> <mi>F</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>n</mi> <mo>,</mo> <mi>q</mi> <mo stretchy="false">)</mo> </mrow> <mo>=</mo> <msub> <mi>t</mi> <mi>F</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>n</mi> <mo>,</mo> <mi>q</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation>. We also discuss some additional remarks and related open problems.</p>

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Supersaturation Beyond Color-Critical Graphs

  • Jie Ma,
  • Long-Tu Yuan

摘要

The supersaturation problem for a given graph F asks for the minimum number \(h_F(n,q)\) h F ( n , q ) of copies of F in an n-vertex graph with \(\textrm{ex}(n,F)+q\) ex ( n , F ) + q edges. Subsequent works by Rademacher, Erdős, and Lovász and Simonovits determine the optimal range of q (which is linear in n) for cliques F such that \(h_F(n,q)\) h F ( n , q ) equals the minimum number \(t_F(n,q)\) t F ( n , q ) of copies of F obtained from a maximum F-free n-vertex graph by adding q new edges. A breakthrough result of Mubayi extends this line of research from cliques to color-critical graphs F, and this was further strengthened by Pikhurko and Yilma who established the equality \(h_F(n,q)=t_F(n,q)\) h F ( n , q ) = t F ( n , q ) for \(1\le q\le \epsilon _F n\) 1 q ϵ F n and sufficiently large n. In this paper, we present several results on the supersaturation problem that extend beyond the existing framework. Firstly, we explicitly construct infinitely many graphs F with restricted properties for which \(h_F(n,q)<q\cdot t_F(n,1)\) h F ( n , q ) < q · t F ( n , 1 ) holds when \(n\gg q\ge 4\) n q 4 , thus refuting a conjecture of Mubayi. Secondly, we extend the result of Pikhurko–Yilma by showing the equality \(h_F(n,q)=t_F(n,q)\) h F ( n , q ) = t F ( n , q ) in the range \(1\le q\le \epsilon _F n\) 1 q ϵ F n for any member F in a diverse and abundant graph family (which includes color-critical graphs, disjoint unions of cliques \(K_r\) K r , and the Petersen graph). Lastly, we prove the existence of a graph F for any positive integer s such that \(h_F(n,q)=t_F(n,q)\) h F ( n , q ) = t F ( n , q ) holds when \(1\le q\le \epsilon _F n^{1-1/s}\) 1 q ϵ F n 1 - 1 / s , and \(h_F(n,q)<t_F(n,q)\) h F ( n , q ) < t F ( n , q ) when \(n^{1-1/s}/\epsilon _F\le q\le \epsilon _F n\) n 1 - 1 / s / ϵ F q ϵ F n , indicating that \(q=\Theta (n^{1-1/s})\) q = Θ ( n 1 - 1 / s ) serves as the threshold for the equality \(h_F(n,q)=t_F(n,q)\) h F ( n , q ) = t F ( n , q ) . We also discuss some additional remarks and related open problems.