2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/28383We show that in a broad class of directed abelian sandpile models that had been expected to have the same exponents as the Dhar-Ramaswamy model, the avalanche exponent depends upon the details of the interaction, calling into question the general existence of universality classes in self organized critical models.Condensed Mattertext