Critical behavior of the three-dimensional contact process

I determine the critical behavior of a nonequilibrium three-dimensional lattice model exhibiting a phase transition to an absorbing state. I study the model in the vicinity of the critical point, and in the subcritical region, via time-dependent Monte Carlo simulations. The method used in the subcritical region is very efficient. The results for the directly measured critical exponents, ν=1.11+/-0.01, η=0.114+/-0.004, and z=1.052+/-0.003, are consistent with those of directed percolation. δ=0.732+/-0.004 is obtained from the hyperscaling relation 4δ+2η=dz, and β=0.813+/-0.011 from β=νδ. These results are the most precise so far for a three-dimensional model with directed percolation critical behavior.