Supersaturation for hereditary properties

Abstract

Let $\mathcal{F}$ be a collection of $r$-uniform hypergraphs, and let $0 < p < 1$. It is known that there exists $c = c(p,\mathcal{F})$ such that the probability of a random $r$-graph in $G(n,p)$ not containing an induced subgraph from $\mathcal{F}$ is $2^{(-c+o(1)){n \choose r}}$. Let each graph in $\mathcal{F}$ have at least $t$ vertices. We show that in fact for every $ε> 0$, there exists $δ= δ(ε, p,\mathcal{F}) > 0$ such that the probability of a random $r$-graph in $G(n,p)$ containing less than $δn^t$ induced subgraphs each lying in $\mathcal{F}$ is at most $2^{(-c+ε){n \choose r}}$. This statement is an analogue for hereditary properties of the supersaturation theorem of Erdős and Simonovits. In our applications we answer a question of Bollobás and Nikiforov.

5 pages, submitted to European Journal of Combinatorics