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arXiv · 2605.04938

The Erd\H{o}s-P\'osa property for prime-length cycles fails (and beyond)

Maximilian Gorsky·Kevin Hendrey·Tony Huynh
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Abstract

We prove that for every $t \in \mathbb{N}$, prime-length cycles do not have the $\frac{1}{t}$-integral Erd\H{o}s-P\'osa property, even when restricted to planar graphs. We in fact prove a more general density result. For every $t \in \mathbb{N}$ and every subset $L \subseteq \mathbb{N}$ with lower density zero, the set of cycles whose length is in $L$ do not have the $\frac{1}{t}$-integral Erd\H{o}s-P\'osa property, even when restricted to planar graphs. We also consider a less restrictive density condition on $L$, called porous, where the complement of $L$ contains arbitrarily long sequences of consecutive integers. We prove that for every porous set $L \subseteq \mathbb{N}$, the set of cycles whose length is in $L$ do not have the Erd\H{o}s-P\'osa property, even when restricted to projective planar graphs. Our results partially answer a question of Gollin, Hendrey, Kwon, Oum, and Yoo [Math. Ann., 393(2):2507-2559, 2025].

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Maximilian Gorsky, Kevin Hendrey, Tony Huynh. 2026-05-06. The Erd\H{o}s-P\'osa property for prime-length cycles fails (and beyond). https://arxiv.org/abs/2605.04938

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