A. Honecker, A PERTURBATIVE APPROACH TO SPECTRUM AND CORRELATION-FUNCTIONS OF THE CHIRAL POTTS-MODEL, Journal of statistical physics, 82(3-4), 1996, pp. 687-741
The massive high-temperature phase of the chiral Potts quantum chain i
s studied using perturbative methods. For the Z(3)-chain we present hi
gh-temperature expansions for the ground-state energy and the dispersi
on relations of the two single-particle states as well as two-particle
stales at general values of the parameters. We also present a perturb
ative argument showing that a large class of massive Z(n)-spin quantum
chains have quasiparticle spectra with n-1 fundamental particles. It
is known from earlier investigations that-at special values of the par
ameters-some of the fundamental particles exist only for limited range
s of the momentum. In these regimes our argument is not rigorous, as o
ne can conclude from a discussion of the radius of convergence of the
perturbation series. We also derive correlation functions from a pertu
rbative evaluation of the ground-state for the Z(3)-chain. In addition
to an exponential decay we observe an oscillating contribution. The o
scillation length seems to be related to the asymmetry of the dispersi
on relations. We show that this relation is exact at special values of
the parameters for general Z(n) using a form factor expansion.