THE OFF-CRITICAL INTEGRABLE ASHKIN-TELLER MODEL

The exact solution of an Ashkin-Teller model, with layer and spatial anisotropy and Z2*Z2 symmetry, is presented. The model is related to the eight-vertex model by a sublattice or orbifold duality and it has the same free energy and magnetisation. The exact solution manifold is a three-dimensional submanifold of the full six-dimensional thermodynamic space. It admits a Z3 symmetry relating three regimes each exhibiting different partial order. In the spatially isotropic case, these regimes are separated by three lines of continuously varying critical behaviour which coalesce at the four-state Potts critical point. The magnetisations and polarisation are derived using corner transfer matrices giving rise to the appearance of chiral and Virasoro characters. The associated critical exponents confirm the known values. In particular, one obtains the value x sigma=1/8 for the magnetic scaling dimension and identify the next-to-leading thermal field.