Unusual corrections to scaling in the 3-state Potts antiferromagnet on a square lattice

At zero temperature, the 3-state antiferromagnetic Potts model on a square lattice maps exactly onto a point of the 6-vertex model whose long-distance behavior is equivalent to that of a free scalar boson. We point out that a t nonzero temperature there are two distinct types of excitation: vortices, which are relevant with renormalization-group eigenvalue 1/2: and non-vort ex unsatisfied bonds, which are strictly marginal and serve only to renorma lize the stiffness coefficient of the underlying free boson. Together these excitations lead to an unusual form for the corrections to scaling: for ex ample, the correlation length diverges as beta equivalent to J/kT --> infin ity according to xi similar to Ae(2 beta)(1+b betae(-beta) + ...), where b is a nonuniversal constant that may nevertheless be determined independentl y. A similar result holds for the staggered susceptibility. These results a re shown to be consistent with the anomalous behavior found in the Monte Ca rlo simulations of Ferreira and Sokal.