A Refutation of the Pach-Tardos Conjecture for 0-1 Matrices
<|reference_start|>A Refutation of the Pach-Tardos Conjecture for 0-1 Matrices: The theory of forbidden 0-1 matrices generalizes Turan-style (bipartite) subgraph avoidance, Davenport-Schinzel theory, and Zarankiewicz-type problems, and has been influential in many areas, such as discrete and computational geometry, the analysis of self-adjusting data structures, and the development of the graph parameter twin width.   The foremost open problems in this area is to resolve the Pach-Tardos conjecture from 2005, which states that if a forbidden pattern $P\in\{0,1\}^{k\times l}$ is the bipartite incidence matrix of an acyclic graph (forest), then $\mathrm{Ex}(P,n) = O(n\log^{C_P} n)$, where $C_P$ is a constant depending only on $P$. This conjecture has been confirmed on many small patterns, specifically all $P$ with weight at most 5, and all but two with weight 6.   The main result of this paper is a clean refutation of the Pach-Tardos conjecture. Specifically, we prove that $\mathrm{Ex}(S_0,n),\mathrm{Ex}(S_1,n) \geq n2^{\Omega(\sqrt{\log n})}$, where $S_0,S_1$ are the outstanding weight-6 patterns. We also prove sharp bounds on the entire class of alternating patterns $(P_t)$, specifically that for every $t\geq 2$, $\mathrm{Ex}(P_t,n)=\Theta(n(\log n/\log\log n)^t)$. This is the first proof of an asymptotically sharp bound that is $\omega(n\log n)$.<|reference_end|>
@article{pettie2024a,
    title={A Refutation of the Pach-Tardos Conjecture for 0-1 Matrices},
    author={Seth Pettie, G'abor Tardos},
    journal={arXiv preprint arXiv:2407.02638},
    year={2024},
    archivePrefix={arXiv},
    eprint={2407.02638},
    primaryClass={math.CO cs.DM}
}