Two conjectures on vertex-disjoint rainbow triangles

Abstract

In 1963, Dirac proved that every $n$-vertex graph has $k$ vertex-disjoint triangles if $n\ge 3k$ and minimum degree $\hat{I}´(G)\ge \frac{n+k}{2}$. The base case $n=3k$ can be reduced to the Corrádi-Hajnál Theorem. Towards a rainbow version of Dirac's Theorem, Hu, Li, and Yang conjectured that for all positive integers $n$ and $k$ with $n\ge 3k$, every edge-colored graph $G$ of order $n$ with $\hat{I}{´}^c(G)\ge \frac{n+k}{2}$ contains $k$ vertex-disjoint rainbow triangles. In another direction, Wu et al. conjectured an exact formula for anti-Ramsey number $ar(n,k{C}_3)$, generalizing the earlier work of Erdős, Sós and Simonovits. The conjecture of Hu, Li, and Yang was confirmed for the cases $k=1$ and $k=2$. However, Lo and Williams disproved the conjecture when $n\le \frac{17k}{5}.$ It is therefore natural to ask whether the conjecture holds for $n=\hat{I}\text{c◯}(k)$. In this paper, we confirm this by showing that the Hu-Li-Yang conjecture holds when $n\ge 42.5k+48$. We disprove the conjecture of Wu et al. and propose a modified conjecture. This conjecture is motivated by previous works due to Allen, Böttcher, Hladký, and Piguet on Turán number of vertex-disjoint triangles.

16 pages