<p>In this work, we consider the class of Cayley graphs known as generalized Paley graphs (GP-graphs for short) given by <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="26_2025_758_Article_IEq1.gif" Format="GIF" Height="23" Rendition="HTML" Resolution="72" Type="Linedraw" Width="229" /> </InlineMediaObject> <EquationSource Format="TEX">\(\Gamma (k,q) = \textrm{Cay}({\mathbb {F}}_q, \{x^k: x\in {\mathbb {F}}_q^* \})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="normal">Γ</mi> <mrow> <mo stretchy="false">(</mo> <mi>k</mi> <mo>,</mo> <mi>q</mi> <mo stretchy="false">)</mo> </mrow> <mo>=</mo> <mtext>Cay</mtext> <mo stretchy="false">(</mo> <msub> <mi mathvariant="double-struck">F</mi> <mi>q</mi> </msub> <mo>,</mo> <mrow> <mo stretchy="false">{</mo> <msup> <mi>x</mi> <mi>k</mi> </msup> <mo>:</mo> <mi>x</mi> <mo>∈</mo> <msubsup> <mi mathvariant="double-struck">F</mi> <mi>q</mi> <mo>∗</mo> </msubsup> <mo stretchy="false">}</mo> </mrow> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation>, where <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="26_2025_758_Article_IEq2.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="18" /> </InlineMediaObject> <EquationSource Format="TEX">\({\mathbb {F}}_q\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi mathvariant="double-struck">F</mi> <mi>q</mi> </msub> </math></EquationSource> </InlineEquation> is a finite field with <i>q</i> elements, both in the directed and undirected case. Hence <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="26_2025_758_Article_IEq3.gif" Format="GIF" Height="17" Rendition="HTML" Resolution="72" Type="Linedraw" Width="53" /> </InlineMediaObject> <EquationSource Format="TEX">\(q=p^m\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>q</mi> <mo>=</mo> <msup> <mi>p</mi> <mi>m</mi> </msup> </mrow> </math></EquationSource> </InlineEquation> with <i>p</i> prime, <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="26_2025_758_Article_IEq4.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="49" /> </InlineMediaObject> <EquationSource Format="TEX">\(m\in {\mathbb {N}}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>m</mi> <mo>∈</mo> <mi mathvariant="double-struck">N</mi> </mrow> </math></EquationSource> </InlineEquation> and one can assume that <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="26_2025_758_Article_IEq5.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="62" /> </InlineMediaObject> <EquationSource Format="TEX">\(k\mid q-1\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>k</mi> <mo>∣</mo> <mi>q</mi> <mo>-</mo> <mn>1</mn> </mrow> </math></EquationSource> </InlineEquation>. We first give the connected components of an arbitrary GP-graph. We show that these components are smaller GP-graphs all isomorphic to each other (generalizing Lim and Praeger’s result from 2009 to the directed case). We then characterize those GP-graphs which are disjoint unions of odd cycles. Finally, we show that <InlineEquation ID="IEq6"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="26_2025_758_Article_IEq6.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="49" /> </InlineMediaObject> <EquationSource Format="TEX">\(\Gamma (k,q)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="normal">Γ</mi> <mo stretchy="false">(</mo> <mi>k</mi> <mo>,</mo> <mi>q</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> is non-bipartite except for the graphs <InlineEquation ID="IEq7"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="26_2025_758_Article_IEq7.gif" Format="GIF" Height="20" Rendition="HTML" Resolution="72" Type="Linedraw" Width="84" /> </InlineMediaObject> <EquationSource Format="TEX">\(\Gamma (2^{m-1},2^m)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="normal">Γ</mi> <mo stretchy="false">(</mo> <msup> <mn>2</mn> <mrow> <mi>m</mi> <mo>-</mo> <mn>1</mn> </mrow> </msup> <mo>,</mo> <msup> <mn>2</mn> <mi>m</mi> </msup> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation>, <InlineEquation ID="IEq8"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="26_2025_758_Article_IEq8.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="49" /> </InlineMediaObject> <EquationSource Format="TEX">\(m \in {\mathbb {N}}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>m</mi> <mo>∈</mo> <mi mathvariant="double-struck">N</mi> </mrow> </math></EquationSource> </InlineEquation>, which are isomorphic to <InlineEquation ID="IEq9"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="26_2025_758_Article_IEq9.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="101" /> </InlineMediaObject> <EquationSource Format="TEX">\(K_2 \sqcup \cdots \sqcup K_2\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>K</mi> <mn>2</mn> </msub> <mo>⊔</mo> <mo>⋯</mo> <mo>⊔</mo> <msub> <mi>K</mi> <mn>2</mn> </msub> </mrow> </math></EquationSource> </InlineEquation>, the disjoint union of <InlineEquation ID="IEq10"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="26_2025_758_Article_IEq10.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="35" /> </InlineMediaObject> <EquationSource Format="TEX">\(2^{m-1}\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mn>2</mn> <mrow> <mi>m</mi> <mo>-</mo> <mn>1</mn> </mrow> </msup> </math></EquationSource> </InlineEquation> copies of <InlineEquation ID="IEq11"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="26_2025_758_Article_IEq11.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="22" /> </InlineMediaObject> <EquationSource Format="TEX">\(K_2\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>K</mi> <mn>2</mn> </msub> </math></EquationSource> </InlineEquation>.</p>

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Connected Components and Non-bipartiteness of Generalized Paley Graphs

  • Ricardo A. Podestá,
  • Denis E. Videla

摘要

In this work, we consider the class of Cayley graphs known as generalized Paley graphs (GP-graphs for short) given by \(\Gamma (k,q) = \textrm{Cay}({\mathbb {F}}_q, \{x^k: x\in {\mathbb {F}}_q^* \})\) Γ ( k , q ) = Cay ( F q , { x k : x F q } ) , where \({\mathbb {F}}_q\) F q is a finite field with q elements, both in the directed and undirected case. Hence \(q=p^m\) q = p m with p prime, \(m\in {\mathbb {N}}\) m N and one can assume that \(k\mid q-1\) k q - 1 . We first give the connected components of an arbitrary GP-graph. We show that these components are smaller GP-graphs all isomorphic to each other (generalizing Lim and Praeger’s result from 2009 to the directed case). We then characterize those GP-graphs which are disjoint unions of odd cycles. Finally, we show that \(\Gamma (k,q)\) Γ ( k , q ) is non-bipartite except for the graphs \(\Gamma (2^{m-1},2^m)\) Γ ( 2 m - 1 , 2 m ) , \(m \in {\mathbb {N}}\) m N , which are isomorphic to \(K_2 \sqcup \cdots \sqcup K_2\) K 2 K 2 , the disjoint union of \(2^{m-1}\) 2 m - 1 copies of \(K_2\) K 2 .