dorsal/arxiv
View SchemaOn the zero-free region for the chromatic polynomial of claw-free graphs with and without induced square and induced diamond
| Authors | Paula M. S. Fialho, Aldo Procacci |
|---|---|
| Categories | |
| ArXiv ID | 2601.06918vv1 |
| URL | https://arxiv.org/abs/2601.06918 |
| License | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ |
Abstract
Given a claw-free graph $G=(V,E)$ with maximum degree $\Delta$, we define the parameter $\kappa\in [0,1]$ as $\kappa={\max_{v\in V}|I_v|\over \lfloor\Delta^2/4\rfloor}$ where $I_v$ is the set of all independent pairs in the neighborhood of $v$. We refer to $\kappa$ as the pair independence ratio of $G$. We prove that for any claw-free graph $G$ with pair independence ratio at most $\kappa$ the zeros of its chromatic polynomial $P_G(q)$ lie inside the disk $D=\{q\in \mathbb{C}:~|q|< C_\kappa^0\Delta\}$, where $C_\kappa^0$ is an increasing function of $\kappa\in [0,1]$. If $G$ is also square-free and diamond free, the function $C_\kappa^0$ can be replaced by a sharper function $C_\kappa^1$. These bounds constitute an improvement upon results recently given by Bencs and Regts in ''Improved bounds on the zeros of the chromatic polynomial of graphs and claw-free graphs''.
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"abstract": "Given a claw-free graph $G=(V,E)$ with maximum degree $\\Delta$,\n we define the parameter $\\kappa\\in [0,1]$ as $\\kappa={\\max_{v\\in V}|I_v|\\over \\lfloor\\Delta^2/4\\rfloor}$ where $I_v$ is the set of all independent pairs in the neighborhood of $v$. We refer to $\\kappa$ as the pair independence ratio of $G$.\n We prove that for any claw-free graph $G$ with pair independence ratio at most $\\kappa$ the zeros of its chromatic polynomial $P_G(q)$ lie inside the disk $D=\\{q\\in \\mathbb{C}:~|q|\u003c C_\\kappa^0\\Delta\\}$, where $C_\\kappa^0$ is an increasing function of $\\kappa\\in [0,1]$. If $G$ is also square-free and diamond free, the function $C_\\kappa^0$ can be replaced by a sharper function $C_\\kappa^1$. These bounds constitute an improvement upon results\n recently given by Bencs and Regts in \u0027\u0027Improved bounds on the zeros of the chromatic polynomial of graphs and claw-free graphs\u0027\u0027.",
"arxiv_id": "2601.06918",
"authors": [
"Paula M. S. Fialho",
"Aldo Procacci"
],
"categories": [
"math.CO"
],
"license": "http://arxiv.org/licenses/nonexclusive-distrib/1.0/",
"title": "On the zero-free region for the chromatic polynomial of claw-free graphs with and without induced square and induced diamond",
"url": "https://arxiv.org/abs/2601.06918",
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