New approach for multicriticality in directed and diode percolation

We present a new and very simple model for treating directed and more general diode-percolation problems by allowing neighboring sites to be joined by up to two independent bonds of opposite orientations. A generalized "break-collapse" method is developed to calculate renormalization-group recursion relations. On the square lattice, a very symmetric phase diagram is obtained which displays multicritical percolation phenomena, and a variety of interesting conductivity transitions are predicted.