The distribution of sandpile groups of random regular graphs

We study the distribution of the sandpile group of random d d -regular graphs. For the directed model, we prove that it follows the Cohen-Lenstra heuristics, that is, the limiting probability that the p p -Sylow subgroup of the sandpile group is a given p p -group P P , is proportional to | A u t ( P ) | − 1 |Aut(P)|⁻¹ . For finitely many primes, these events get independent in the limit. Similar results hold for undirected random regular graphs, where for odd primes the limiting distributions are the ones given by Clancy, Leake, and Payne. This answers an open question of Frieze and Vu whether the adjacency matrix of a random regular graph is invertible with high probability. Note that for directed graphs this was recently proved by Huang. It also gives an alternate proof of a theorem of Backhausz and Szegedy.