Anatomy of a young giant component in the random graph

We provide a complete description of the giant component of the Erdős-Rényi random graph G(n, p) as soon as it emerges from the scaling window, i.e., for p = (1 + ε)/n where εn → ∞ and ε = o(1). Our description is particularly simple for ε = o(n), where the giant component C1 is contiguous with the following model (i.e., every graph property that holds with high probability for this model also holds w.h.p. for C1). Let Z be normal with mean 2 3 εn and variance εn, and let K be a random 3-regular graph on 2⌊Z⌋ vertices. Replace each edge of K by a path, where the path lengths are i.i.d. geometric with mean 1/ε. Finally, attach an independent Poisson(1 − ε)-Galton-Watson tree to each vertex. A similar picture is obtained for larger ε = o(1), in which case the random 3-regular graph is replaced by a random graph with Nk vertices of degree k for k ≥ 3, where Nk has mean and variance of order ε n. This description enables us to determine fundamental characteristics of the supercritical random graph. Namely, we can infer the asymptotics of the diameter of the giant component for any rate of decay of ε, as well as the mixing time of the random walk on C1.