On the Phase Diagram of the q->1 Extended Potts Model and Lattice Animal Collapse

The phase diagram of the two-dimensional extended q-states Potts model is investigated in the q->1 limit. This is equivalent to studying the phase diagram of a two-dimensional infinite interacting lattice animal. An exact solution on the Bethe lattice and a Migdal-Kadanoff renormalization group calculation predict a line of theta transitions from an extended to a compact phase in the lattice animal. We compare this with the phase diagram predicted from previous numerical studies.