Transport on directed percolation clusters.

We study random lattice networks consisting of resistorlike and diodelike bonds. For investigating the transport properties of these random resistor diode networks we introduce a field-theoretic Hamiltonian amenable to renormalization group analysis. We focus on the average two-port resistance at the transition from the nonpercolating to the directed percolating phase and calculate the corresponding resistance exponent straight phi to two-loop order. Moreover, we determine the backbone dimension D(B) of directed percolation clusters to two-loop order. We obtain a scaling relation for D(B) that is in agreement with well known scaling arguments.