English

Two conjectures on vertex-disjoint rainbow triangles

Combinatorics 2025-10-03 v1

Abstract

In 1963, Dirac proved that every nn-vertex graph has kk vertex-disjoint triangles if n3kn\geq 3k and minimum degree δ(G)n+k2\delta(G)\geq \frac{n+k}{2}. The base case n=3kn=3k can be reduced to the Corr\'adi-Hajn\'al Theorem. Towards a rainbow version of Dirac's Theorem, Hu, Li, and Yang conjectured that for all positive integers nn and kk with n3kn\geq 3k, every edge-colored graph GG of order nn with δc(G)n+k2\delta^c(G)\geq \frac{n+k}{2} contains kk vertex-disjoint rainbow triangles. In another direction, Wu et al. conjectured an exact formula for anti-Ramsey number ar(n,kC3)ar(n,kC_3), generalizing the earlier work of Erd\H{o}s, S\'os and Simonovits. The conjecture of Hu, Li, and Yang was confirmed for the cases k=1k=1 and k=2k=2. However, Lo and Williams disproved the conjecture when n17k5.n\leq \frac{17k}{5}. It is therefore natural to ask whether the conjecture holds for n=Ω(k)n=\Omega(k). In this paper, we confirm this by showing that the Hu-Li-Yang conjecture holds when n42.5k+48n\ge 42.5k+48. We disprove the conjecture of Wu et al. and propose a modified conjecture. This conjecture is motivated by previous works due to Allen, B\"{o}ttcher, Hladk\'{y}, and Piguet on Tur\'an number of vertex-disjoint triangles.

Keywords

Cite

@article{arxiv.2510.01880,
  title  = {Two conjectures on vertex-disjoint rainbow triangles},
  author = {Xu Liu and Bo Ning and Yuting Tian},
  journal= {arXiv preprint arXiv:2510.01880},
  year   = {2025}
}

Comments

16 pages

R2 v1 2026-07-01T06:12:56.386Z