Critical exponents of the pair contact process with diffusion

We study the pair contact process with diffusion (PCPD) using Monte Carlo simulations, and concentrate on the decay of the particle density rho with time, near its critical point, which is assumed to follow rho(t) approximate to ct(-delta) + c(2)t(-delta 2) + ... . This model is known for its slow convergence to the asymptotic critical behavior; we therefore pay particular attention to finite-time corrections. We find that at the critical point, the ratio of rho and the pair density rho(p) converges to a constant, indicating that both densities decay with the same power law. We show that under the assumption delta(2) approximate to 2 delta, two of the critical exponents of the PCPD model are delta = 0.165(10) and beta = 0.31(4), consistent with those of the directed percolation (DP) model.