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, ${\nu }_{\perp }=2\mathrm{}$, $z=2\mathrm{}$, $\alpha =1\mathrm{}/2$, and $\beta =2\mathrm{}$ in one dimension for all $N>\mathrm{}1\mathrm{}$. Direct numerical simulations confirm our prediction. When the diffusion coefficients for different species are not identical, ${\nu }_{\perp }$ and $\beta$ vary continuously with the ratios between the coefficients.