Numerical transfer-matrix study of metastability in the d=2 Ising model

We apply a generalized transfer-matrix method to the d=2 Ising ferromagnet at H≠0 and T<T_c to obtain complex constrained free energies. Although the method does not explicitly introduce droplets, the imaginary parts of those constrained free energies that correspond to the metastable state are accurately predicted by a field-theoretical droplet model. The free energy of a critical droplet is given by an equilibrium Wulff construction, and we find evidence for Goldstone modes on its surface. These results indicate that our approach provides a nonperturbative numerical continuation of the free energy around the essential singularity at H=0.