Blow-up lemmas for sparse graphs

Abstract

The blow-up lemma states that a system of super-regular pairs contains all bounded degree spanning graphs as subgraphs that embed into a corresponding system of complete pairs. This lemma has far-reaching applications in extremal combinatorics. We prove sparse analogues of the blow-up lemma for subgraphs of random and of pseudorandom graphs. Our main results are the following three sparse versions of the blow-up lemma: one for embedding spanning graphs with maximum degree $Δ$ in subgraphs of $G(n,p)$ with $p=C(\log n/n)^{1/Δ}$; one for embedding spanning graphs with maximum degree $Δ$ and degeneracy $D$ in subgraphs of $G(n,p)$ with $p=C_Δ\big(\log n/n\big)^{1/(2D+1)}$; and one for embedding spanning graphs with maximum degree $Δ$ in $(p,cp^{\max(4,(3Δ+1)/2)}n)$-bijumbled graphs. We also consider various applications of these lemmas.