Coloring outside the lines: Spectral bounds for generalized hypergraph colorings

Lies Beers; Raffaella Mulas

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arXiv · 2506.17659

Coloring outside the lines: Spectral bounds for generalized hypergraph colorings

Lies Beers·Raffaella Mulas

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Abstract

It is known that, for an oriented hypergraph with (vertex) coloring number $\chi$ and smallest and largest normalized Laplacian eigenvalues $\lambda_1$ and $\lambda_N$, respectively, the inequality $\chi\geq (\lambda_N-\lambda_1)/\min\{\lambda_N-1,1-\lambda_1\}$ holds. We provide necessary conditions for oriented hypergraphs for which this bound is tight. Focusing on $c$-uniform unoriented hypergraphs, we then generalize the bound to the setting of \emph{$d$-proper colorings}: colorings in which no edge contains more than $d$ vertices of the same color. We also adapt our proof techniques to derive analogous spectral bounds for \emph{$d$-improper colorings} of graphs and for edge colorings of hypergraphs. Moreover, for all coloring notions considered, we provide necessary conditions under which the bound is an equality.

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Lies Beers, Raffaella Mulas. 2025-06-21. Coloring outside the lines: Spectral bounds for generalized hypergraph colorings. https://arxiv.org/abs/2506.17659

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