Transition from Tracy-Widom to Gaussian fluctuations of extremal eigenvalues of sparse ErdH{o}s-Renyi graphs

We consider the statistics of the extreme eigenvalues of sparse random matrices, a class of random matrices that includes the normalized adjacency matrices of the ErdH{o}s-Renyi graph $G(N,p)$. Tracy-Widom fluctuations of the extreme eigenvalues for $pgg N^{-2/3}$ was proved in [17,46]. We prove that there is a crossover in the behavior of the extreme eigenvalues at $psim N^{-2/3}$. In the case that $N^{-7/9}ll pll N^{-2/3}$, we prove that the extreme eigenvalues have asymptotically Gaussian fluctuations. Under a mean zero condition and when $p=CN^{-2/3}$, we find that the fluctuations of the extreme eigenvalues are given by a combination of the Gaussian and the Tracy-Widom distribution. These results show that the eigenvalues at the edge of the spectrum of sparse ErdH{o}s-Renyi graphs are less rigid than those of random $d$-regular graphs [4] of the same average degree.