Odd Cycle Decompositions

Source abstract

We determine the asymptotic minimum-degree threshold for decompositions into cycles of every fixed odd length. We prove that, for each odd integer $\ell\ge3$, every $\eps>0$ and sufficiently large $n$, every $n$-vertex $C_\ell$-divisible graph $G$ with minimum degree $δ(G)\ge (\ell/(2\ell-2)+\eps)n$ has a $C_\ell$-decomposition, where $C_{\ell}$ denotes the cycle of length $\ell$. The constant is best possible. This settles the remaining cases $\ell=5,7,\ldots,71$ and completes the determination of the thresholds for all odd cycles. The proof combines the condensation approach of Bryant et al. with a sharp weighted-triangle fractional decomposition theorem. Its key step is a rescaling of the dual edge weights that allows us to apply a quantitative discharging estimate from the breakthrough of Delcourt and Postle on Nash--Williams' triangle decomposition conjecture.