  We study the nonequilibrium critical behavior of the pair contact process
with diffusion (PCPD) by means of nonperturbative functional renormalization
group techniques. We show that usual perturbation theory fails because the
effective potential develops a nonanalyticity at a finite length scale:
Perturbatively forbidden terms are dynamically generated and the flow can be
continued once they are taken into account. Our results suggest that the
critical behavior of PCPD can be either in the directed percolation or in a new
(conjugated) universality class.
