Operator content of the Ashkin-Teller quantum chain, superconformal and Zamolodchikov-Fateev invariance. II. Boundary conditions compatible with the torus

For pt. I, see ibid., vol. 20, no.8, p.L479-85 (1987). The authors present the operator content of the Ashkin-Teller quantum chain with eight boundary conditions corresponding to the eight elements of the group D 4 which gives the global symmetry of the system. This operator content is a conjecture based on an extensive numerical study and was proven to be correct at the Ising decoupling point. For the values of the coupling constant where N=2, superconformal invariance was seen for free boundary conditions. The situation is now more complex. One finds sectors which have N=2 and N=1 superconformal invariance and sectors which have no superconformal invariance at all. If, however, they combine the 'wrong' sectors of the spectra which correspond to two different values of the coupling constant, a new symmetry shows up. They also analyse the operator content at the Fateev-Zamolodchikov points. Here the 'wrong' sectors can be described by a few new primary fields.