Does Hard Core Interaction Change Absorbing-Type Critical Phenomena?

It has been generally believed that hard core interaction is irrelevant to absorbing-type critical phenomena because the particle density is so low near an absorbing phase transition. We study the effect of hard core interaction on the N-species branching annihilating random walks with two offspring and report that hard core interaction drastically changes the absorbing-type critical phenomena in a nontrivial way. Through a Langevin equation-type approach, we predict analytically the values of the scaling exponents, ν_⊥ = 2, z = 2, α = 1/2, and β = 2 in one dimension for all N>1. Direct numerical simulations confirm our prediction. When the diffusion coefficients for different species are not identical, ν_⊥ and β vary continuously with the ratios between the coefficients.