Homomorphic-core phase transition threshold in Erd\H{o}s--R\'{e}nyi random graphs

Abstract

It is shown in this manuscript that a random graph $G$ drawn from the Erd\H{o}s--R\'{e}nyi model $\mathcal{G}(n,p)$ with \[ p=p(n)\leq 1/2, \qquad \lim_{n\to+\infty}(np-\log n-\log\log n)=+\infty, \] is a homomorphic core, i.e., every homomorphism from $G$ to itself is an automorphism. This implies tight ETH-based lower bounds of the subgraph isomorphism problem for almost all $k$-vertex patterns with polynomial average degree.