BAK-TANG-WIESENFELD SANDPILE MODEL AROUND THE UPPER CRITICAL DIMENSION

We consider the Bak-Tang-Wiesenfeld sandpile model [Phys. Rev. Lett. 5 9, 381 (1987); Phys. Rev. A 38, 364 (1988)] on square lattices in diff erent dimensions (D less than or equal to 6). A finite-size scaling an alysis of the avalanche probability distributions yields the values of the distribution exponents, the dynamical exponent. and the dimension of the avalanches. Above the upper critical dimension D-u=4 the expon ents equal the known mean-field values. An analysis of the area probab ility distributions indicates that the avalanches are fractal above th e critical dimension.