Year: 2026
Type: preprint
Abstract: A graph $H$ is $K_{r+1}$-Turán-good if, for every sufficiently large $n$, the Turán graph $T_r(n)$ maximizes the number of copies of $H$ among all $n$-vertex $K_{r+1}$-free graphs, and it is strictly $K_{r+1}$-Turán-good when this extremal graph is unique. Morrison, Nir, Norin, Rzążewski and Wesolek proved that for every graph $H$ with at least one edge, when $r\ge 300v(H)^9$, $H$ is $K_{r+1}$-Turán-good. They asked whether the above bound could be reduced to quadratic order in $v(H)$. In this paper, we answer their question affirmatively, and give a stronger result. We prove that there is an absolute constant $C>0$ such that every graph $H$ with at least one edge is strictly $K_{r+1}$-Turán-good whenever $r\ge Cv(H)$. Our proof uses a substantially different cluster method based on polymer models. Besides proving the vertex-linear Turán-good threshold, this method appears to have further applications. As one illustration, we prove that for every graph $H$ with at least one edge, the normalized chromatic polynomial $P_H(x)/x^{v(H)}$ is strictly increasing for every real $x\ge CΔ(H)$, which strengthens the previously best result where $x\ge CΔ(H)^{3/2}$. This proves a conjecture of Fadnavis.
Source: arXiv (Cornell University)
Authors: Zhao, Xiamiao, Kang, Liying, Wang, Yuanpei
Language: English
Subfield: Discrete Mathematics and Combinatorics
Field: Mathematics
Domain: Physical Sciences
Open Access status: green
Awards: G2877621488, G478768364, G8911783418
OpenAlex ID: W7214119980