Multicritical behavior in coupled directed percolation processes

Abstract

We study a hierarchy of directed percolation (DP) processes for particle species A, B, . . ., unidirectionally coupled via the reactions A → B, . . .. When the DP critical points at all levels coincide, multicritical behavior emerges, with density exponents β(k) which are markedly reduced at each hierarchy level k ≥ 2. We compute the fluctuation corrections to β(2) to O(ϵ = 4 − d) using field-theoretic renormalization group techniques. Monte Carlo simulations are employed to determine the new exponents in dimensions d ≤ 3.