<p>A subset of <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="454_2025_748_Article_IEq1.gif" Format="GIF" Height="22" Rendition="HTML" Resolution="72" Type="Linedraw" Width="18" /> </InlineMediaObject> <EquationSource Format="TEX">\({\mathbb {F}}_q^2\)</EquationSource> </InlineEquation> is called an arc if it does not contain three collinear points. We show that there are at most <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="454_2025_748_Article_IEq4.gif" Format="GIF" Height="20" Rendition="HTML" Resolution="72" Type="Linedraw" Width="64" /> </InlineMediaObject> <EquationSource Format="TEX">\(\left( {\begin{subarray}{c}(1 + o(1))q\\ m\end{subarray}}\right) \)</EquationSource> </InlineEquation> arcs of size <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="454_2025_748_Article_IEq5.gif" Format="GIF" Height="21" Rendition="HTML" Resolution="72" Type="Linedraw" Width="130" /> </InlineMediaObject> <EquationSource Format="TEX">\(m \gg q^{1/2} (\log q)^{3/2}\)</EquationSource> </InlineEquation>, nearly matching a trivial lower bound of <InlineEquation ID="IEq6"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="454_2025_748_Article_IEq6.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="24" /> </InlineMediaObject> <EquationSource Format="TEX">\(\left( {\begin{subarray}{c}q\\ m\end{subarray}}\right) \)</EquationSource> </InlineEquation>. This was previously known to hold for <InlineEquation ID="IEq7"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="454_2025_748_Article_IEq7.gif" Format="GIF" Height="21" Rendition="HTML" Resolution="72" Type="Linedraw" Width="119" /> </InlineMediaObject> <EquationSource Format="TEX">\(m \gg q^{2/3} (\log q)^3\)</EquationSource> </InlineEquation>, by a result of Bhowmick and Roche-Newton. The lower bound on <i>m</i> is best possible up to a logarithmic factor.</p>

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The Number of Arcs in \({\mathbb {F}}_q^2\) of a Given Cardinality

  • Rajko Nenadov

摘要

A subset of \({\mathbb {F}}_q^2\) is called an arc if it does not contain three collinear points. We show that there are at most \(\left( {\begin{subarray}{c}(1 + o(1))q\\ m\end{subarray}}\right) \) arcs of size \(m \gg q^{1/2} (\log q)^{3/2}\) , nearly matching a trivial lower bound of \(\left( {\begin{subarray}{c}q\\ m\end{subarray}}\right) \) . This was previously known to hold for \(m \gg q^{2/3} (\log q)^3\) , by a result of Bhowmick and Roche-Newton. The lower bound on m is best possible up to a logarithmic factor.