An exact mapping between loop-erased random walks and an interacting field theory with two fermions and one boson

We give a simplified proof for the equivalence of loop-erased random walks to a lattice model containing two complex fermions, and one complex boson. This equivalence works on an arbitrary directed graph. Specifying to the $d$-dimensional hypercubic lattice, at large scales this theory reduces to a scalar $phi^4$-type theory with two complex fermions, and one complex boson. While the path integral for the fermions is the Berezin integral, for the bosonic field we can either use a complex field $phi(x)in mathbb C$ (standard formulation) or a nilpotent one satisfying $phi(x)^2 =0$. We discuss basic properties of the latter formulation, which has distinct advantages in the lattice model.