English

Large monochromatic components in 3-edge-colored Steiner triple systems

Combinatorics 2020-02-11 v3

Abstract

It is known that in any rr-coloring of the edges of a complete rr-uniform hypergraph, there exists a spanning monochromatic component. Given a Steiner triple system on nn vertices, what is the largest monochromatic component one can guarantee in an arbitrary 3-coloring of the edges? Gy\'arf\'as proved that (2n+3)/3(2n+3)/3 is an absolute lower bound and that this lower bound is best possible for infinitely many nn. On the other hand, we prove that for almost all Steiner triple systems the lower bound is actually (1o(1))n(1-o(1))n. We obtain this result as a consequence of a more general theorem which shows that the lower bound depends on the size of a largest \emph{3-partite hole} (that is, sets X1,X2,X3X_1, X_2, X_3 with X1=X2=X3|X_1|=|X_2|=|X_3| such that no edge intersects all of X1,X2,X3X_1, X_2, X_3) in the Steiner triple system (Gy\'arf\'as previously observed that the upper bound depends on this parameter). Furthermore, we show that this lower bound is tight unless the coloring has a particular structure. We also suggest a variety of other Ramsey problems in the setting of Steiner triple systems.

Keywords

Cite

@article{arxiv.1908.00837,
  title  = {Large monochromatic components in 3-edge-colored Steiner triple systems},
  author = {Louis DeBiasio and Michael Tait},
  journal= {arXiv preprint arXiv:1908.00837},
  year   = {2020}
}

Comments

Updated to address referee comments; to appear in Journal of Combinatorial Designs

R2 v1 2026-06-23T10:38:12.545Z