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Supersaturation Beyond Color-Critical Graphs
Combinatorica ( IF 1.0 ) Pub Date : 2025-03-14 , DOI: 10.1007/s00493-025-00143-5
Jie Ma , Long-Tu Yuan

The supersaturation problem for a given graph F asks for the minimum number \(h_F(n,q)\) of copies of F in an n-vertex graph with \(\textrm{ex}(n,F)+q\) 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 \(h_F(n,q)\) equals the minimum number \(t_F(n,q)\) 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 \(h_F(n,q)=t_F(n,q)\) for \(1\le q\le \epsilon _F n\) 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 \(h_F(n,q)<q\cdot t_F(n,1)\) holds when \(n\gg q\ge 4\), thus refuting a conjecture of Mubayi. Secondly, we extend the result of Pikhurko–Yilma by showing the equality \(h_F(n,q)=t_F(n,q)\) in the range \(1\le q\le \epsilon _F n\) for any member F in a diverse and abundant graph family (which includes color-critical graphs, disjoint unions of cliques \(K_r\), and the Petersen graph). Lastly, we prove the existence of a graph F for any positive integer s such that \(h_F(n,q)=t_F(n,q)\) holds when \(1\le q\le \epsilon _F n^{1-1/s}\), and \(h_F(n,q)<t_F(n,q)\) when \(n^{1-1/s}/\epsilon _F\le q\le \epsilon _F n\), indicating that \(q=\Theta (n^{1-1/s})\) serves as the threshold for the equality \(h_F(n,q)=t_F(n,q)\). We also discuss some additional remarks and related open problems.



中文翻译:


超出颜色关键图形的过饱和度



给定图 F 的过饱和度问题要求在具有 \(\textrm{ex}(n,F)+q\) 条边的 n 顶点图中 F 副本的最小数量 \(h_F(n,q)\) 个。Rademacher、Erdős、Lovász 和 Simonovits 的后续工作确定了团 Fq 的最佳范围(在 n 中是线性的),使得 \(h_F(n,q)\) 等于通过添加 q 条新边从最大无 F n 顶点图中获得的 F 副本的最小数量 \(t_F(n,q)\)。Mubayi 的一个突破性成果将这一研究路线从派系扩展到颜色关键图 F,Pikhurko 和 Yilma 进一步加强了这一点,他们为 \(1\le q\le \epsilon _F n\) 建立了相等式 \(h_F(n,q)=t_F(n,q)\) 和足够大的 n。在本文中,我们提出了超越现有框架的过饱和度问题的几个结果。首先,我们显式构造了无限多个具有受限属性的图 F,当 \(n\gg q\ge 4\)\(h_F(n,q)<q\cdot t_F(n,1)\) 成立,从而反驳了 Mubayi 的猜想。其次,我们扩展了 Pikhurko-Yilma 的结果,显示了多样化和丰富的图族(包括颜色关键图、派系 \(K_r\) 的不相交联合和彼得森图)中任何成员 F\(1\le q\le \le \epsilon _F n\) 范围内的等式 \(h_F(n,q)=t_F(n,q)\)。 最后,我们证明了任何正整数 s 存在图 F,使得 \(h_F(n,q)=t_F(n,q)\)\(1\le q\le q\le \epsilon _F n^{1-1/s}\) 时成立,当 \(n^{1-1/s}/\epsilon _F\le q\le \epsilon _F n\)\(h_F(n,q)<t_F(n,q)\) 成立, 表示 \(q=\Theta (n^{1-1/s})\) 作为相等 \(h_F(n,q)=t_F(n,q)\) 的阈值。我们还讨论了一些额外的评论和相关的未解决的问题。

更新日期:2025-03-14
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