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arXiv · 2602.11502

Turán extremal graphs vs. Signless Laplacian spectral Turán extremal graphs

Ming-Zhu Chen·Ya-Lei Jin·Peng-Li Zhang·Xiao-Dong Zhang
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Abstract

Let $F$ be a graph with chromatic number $χ(F) = r+1$. Denote by $ex(n, F)$ and $Ex(n, F)$ the Turán number and the set of all extremal graphs for $F$, respectively. In addition, $ex_{ssp}(n, F)$ and $Ex_{ssp}(n, F)$ are the maximum signless Laplacian spectral radius of all $n$-vertex $F$-free graphs and the set of all $n$-vertex $F$-free graphs with signless Laplacian spectral radius $ex_{ssp}(n, F)$, respectively. It is known that $Ex_{ssp}(n, F)\supset Ex(n, F)$ if $F$ is a triangle. In this paper, employing the regularity method and Füredi's stability theorem, we prove that for a given graph $F$ and $r\geqslant 3$, if $ex(n, F) = t_r(n)+O(1)$, then $ Ex_{ssp}(n, F) \subseteq Ex(n, F)$ for sufficiently large $n$, where $t_r(n)$ is the number of edges in the Turán graph $T_r(n)$.

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Ming-Zhu Chen, Ya-Lei Jin, Peng-Li Zhang, Xiao-Dong Zhang. 2026-02-12. Turán extremal graphs vs. Signless Laplacian spectral Turán extremal graphs. https://arxiv.org/abs/2602.11502

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