UNIVERSALITY CLASSES IN ISOTROPIC, ABELIAN, AND NON-ABELIAN SANDPILE MODELS

Universality in isotropic, Abelian, and non-Abelian, sandpile models i s examined using extensive numerical simulations. To characterize the critical behavior we employ an extended set of critical exponents, geo metric features of the avalanches, as well as scaling functions descri bing the time evolution of average quantities such as the area and siz e during the avalanche. Comparing between the Abelian Bak-Tang-Wiesenf edd model [P. Bak, C. Tang, and K. Wiensenfeld, Phys. Rev. Lett. 59, 3 81 (1987)] and the non-Abelian models introduced by Manna [S. S. Manna , J. Phys. A 24, L363 (1991)] and Zhang [Ti. C. Zhang, Phys. Rev. Lett . 63, 470 (1989)] we find strong indications that each one of these mo dels belongs to a distinct universality class.