Blow-up lemma for cycles in sparse random graphs

TL;DR

This paper extends the sparse blow-up lemma to cycles in random graphs, enabling new results on cycle factors and resilience in sparse graph settings, surpassing previous limitations for certain degrees and densities.

Contribution

It introduces a sparse blow-up lemma for all cycles, improving upon prior results limited to small degrees and specific structures, and applies it to cycle factor resilience.

Findings

Established a blow-up lemma for all cycles in sparse random graphs.

Resolved the resilience of cycle factors in sparse random graphs.

Achieved near-optimal density conditions for cycle embeddings.

Abstract

In a recent work, Allen, B\"{o}ttcher, H\`{a}n, Kohayakawa, and Person provided a first general analogue of the blow-up lemma applicable to sparse (pseudo)random graphs thus generalising the classic tool of Koml\'{o}s, S\'{a}rk\"{o}zy, and Szemer\'{e}di. Roughly speaking, they showed that with high probability in the random graph $G_{n,p}$ for $p \geq C(\log n/n)^{1/\Delta}$, sparse regular pairs behave similarly as complete bipartite graphs with respect to embedding a spanning graph $H$ with $\Delta(H) \leq \Delta$. However, this is typically only optimal when $\Delta \in \{2,3\}$ and $H$ either contains a triangle ($\Delta = 2$) or many copies of $K_4$ ($\Delta = 3$). We go beyond this barrier for the first time and present a sparse blow-up lemma for cycles $C_{2k-1}, C_{2k}$, for all $k \geq 2$, and densities $p \geq Cn^{-(k-1)/k}$, which is in a way best possible. As an application of our blow-up lemma we fully resolve a question of Nenadov and \v{S}kori\'{c} regarding resilience of cycle factors in sparse random graphs.