English

$K_4^-$-free triple systems without large stars in the complement

Combinatorics 2025-04-09 v1

Abstract

The nn-star SnS_n is the nn-vertex triple system with (n12){n-1 \choose 2} edges all of which contain a fixed vertex, and K4K_4^- is the unique triple system with four vertices and three edges. We prove that the Ramsey number r(K4,Sn)r(K_4^-, S_n) has order of magnitude n2/lognn^2 /\log n. This confirms a conjecture of Conlon, Fox, He, Suk, Verstra\"ete and the first author. It also generalizes the well-known bound of Kim for the graph Ramsey number r(3,n)r(3,n), as the link of any vertex in a K4K_4^--free triple system is a triangle-free graph. Our method builds on the approach of Guo and Warnke who adapted Kim's lower bound for r(3,n)r(3,n) to the pseudorandom setting.

Keywords

Cite

@article{arxiv.2504.06076,
  title  = {$K_4^-$-free triple systems without large stars in the complement},
  author = {Dhruv Mubayi and Nicholas Spanier},
  journal= {arXiv preprint arXiv:2504.06076},
  year   = {2025}
}

Comments

35 pages

R2 v1 2026-06-28T22:50:55.924Z