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Generalized Paley graphs and their complete subgraphs of orders three and four
Research in the Mathematical Sciences ( IF 1.2 ) Pub Date : 2021-03-09 , DOI: 10.1007/s40687-021-00254-7
Madeline Locus Dawsey , Dermot McCarthy

Let \(k \ge 2\) be an integer. Let q be a prime power such that \(q \equiv 1 ({\mathrm{mod}}\,\,k)\) if q is even, or, \(q \equiv 1 ({\mathrm{mod}}\,\,2k)\) if q is odd. The generalized Paley graph of order q, \(G_k(q)\), is the graph with vertex set \(\mathbb {F}_q\) where ab is an edge if and only if \({a-b}\) is a kth power residue. We provide a formula, in terms of finite field hypergeometric functions, for the number of complete subgraphs of order four contained in \(G_k(q)\), \(\mathcal {K}_4(G_k(q))\), which holds for all k. This generalizes the results of Evans, Pulham and Sheehan on the original (\(k=2\)) Paley graph. We also provide a formula, in terms of Jacobi sums, for the number of complete subgraphs of order three contained in \(G_k(q)\), \(\mathcal {K}_3(G_k(q))\). In both cases, we give explicit determinations of these formulae for small k. We show that zero values of \(\mathcal {K}_4(G_k(q))\) (resp. \(\mathcal {K}_3(G_k(q))\)) yield lower bounds for the multicolor diagonal Ramsey numbers \(R_k(4)=R(4,4,\ldots ,4)\) (resp. \(R_k(3)\)). We state explicitly these lower bounds for small k and compare to known bounds. We also examine the relationship between both \(\mathcal {K}_4(G_k(q))\) and \(\mathcal {K}_3(G_k(q))\), when q is prime, and Fourier coefficients of modular forms.



中文翻译:

广义Paley图及其三阶和四阶的完整子图

\(k \ ge 2 \)为整数。如果q是偶数,则令q\(q \ equiv 1({\ mathrm {mod}} \,\,k)\)的素数,或者\(q \ equiv 1({\ mathrm {mod} } \,\,2k)\)如果q为奇数。顺序的广义佩利图形q\(G_k(Q)\) ,是与顶点集合的曲线\(\ mathbb {F} _q \) ,其中AB是边缘当且仅当\({AB} \)是一个ķ次方残基。我们提供了一个基于有限域超几何函数的公式,用于\(G_k(q)\)中包含的四阶完整子图的数量,\(\ mathcal {K} _4(G_k(q))\),它适用于所有k。这将在原始(\(k = 2 \))Paley图上推广Evans,Pulham和Sheehan的结果。我们还根据Jacobi和提供了一个公式,用于\(G_k(q)\)\(\ mathcal {K} _3(G_k(q))\)中包含的三阶完整子图的数量。在这两种情况下,我们都会为小k明确确定这些公式。我们证明\(\ mathcal {K} _4(G_k(q))\)(resp。  \(\ mathcal {K} _3(G_k(q))\))的零值产生多色对角线Ramsey的下限数字\(R_k(4)= R(4,4,\ ldots,4)\)(分别为 \(R_k(3)\))。我们为小k明确声明这些下限,并与已知范围进行比较。当q为素数时,我们还检查了\(\ mathcal {K} _4(G_k(q))\)\(\ mathcal {K} _3(G_k(q))\)之间的关系,以及模块化形式。

更新日期:2021-03-09
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