The McCoy-Roan integral representation for gaps of the integrable Z_n- symmetric Chiral Potts quantum chain is used to calculate the boundary of the incommensurable phase for various n. In the limit n -> \infty an analytic formula for this phase boundary is obtained. The McCoy-Roan formula gives the gaps in terms of a rapidity. For the lowest gap we conjecture the relation of this rapidity to the physical momentum in the high-temperature limit using symmetry properties and comparing the McCoy-Roan formula to high-temperature expansions and finite-size data.
The McCoy-Roan integral representation for gaps of the integrable Z_n- symmetric Chiral Potts quantum chain is used to calculate the boundary of the incommensurable phase for various n. In the limit n -> \infty an analytic formula for this phase boundary is obtained. The McCoy-Roan formula gives the gaps in terms of a rapidity. For the lowest gap we conjecture the relation of this rapidity to the physical momentum in the high-temperature limit using symmetry properties and comparing the McCoy-Roan formula to high-temperature expansions and finite-size data.
The massive high-temperature phase of the chiral Potts quantum chain is studied using perturbative methods. For the Z_3-chain we present high-temperature expansions for the groundstate energy and the dispersion relations of the two single-particle states as well as two-particle states at general values of the parameters. We also present a perturbative 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 parameters- some of the fundamental particles exist only for limited ranges of the momentum. In these regimes our argument is not rigorous as one can conclude from a discussion of the radius of convergence of the perturbation series. We also derive correlation functions from a perturbative evaluation of the groundstate for the Z_3-chain. In addition to an exponential decay we observe an oscillating contribution. The oscillation length seems to be related to the asymmetry of the dispersion relations. We show that this relation is exact at special values of the parameters for general Z_n using a form factor expansion.
The authors calculate the lowest translationally invariant levels of the Z 3 - and Z 4 -symmetrical chiral Potts quantum chains, using numerical diagonalization of the Hamiltonian for N<or=12 and N<or=10 sites, respectively, and extrapolating n to infinity . In the high-temperature massive phase they find that the pattern of the low-lying zero momentum levels can be explained assuming the existence of n-1 particles carrying Z n charges Q=1, . . ., n-1 (mass m Q ), and their scattering states. In the superintegrable case the masses of the n-1 particles become proportional to their respective charges: m Q =Qm 1 . Exponential convergence in N is observed for the single-particle gaps, while power convergence is seen for the scattering levels. They also verify that qualitatively the same pattern appears for the self-dual and integrable cases. For general Z n they show that the energy-momentum relations of the particles show a parity nonconservation asymmetry which for very high temperatures is exclusive due to the presence of a macroscopic momentum P m =(1-2Q/n) phi , where phi is the chiral angle and Q is the Z n charge of the respective particle.
Phase diagram and two-particle structure of the Z3-chiral Potts model
We calculate the low-lying part of the spectrum of the Z3-symmetrical chiral Potts quantum chain in its self-dual and integrable versions, using numerical diagonalisation of the hamiltonian for N≤12 sites and extrapolation $N \ra \infty$. From the sequences of levels crossing we show that the massive phases have oscillatory correlation functions. We calculate the wave vector scaling exponent. In the high-temperature massive phase the pattern of the low-lying levels can be explained assuming the existence of two particles, with Z3-charge Q=1 and Q=2, and their scattering states. In the superintegrable case the Q=2-particle has twice the mass of the Q=1-particle. Exponential convergence in N is observed for the single particle gaps, while power convergence is seen for the scattering levels. In the high temperature limit of the self-dual model the parity violation in the particle dispersion relation is equivalent to the presence of a macroscopic momentum $P_m = \pm \vph/3$, where $\vph$ is the chiral angle.
In honor of Onsager’s ninetieth birthday, we like to review some exact results obtained so far in the chiral Potts models and to translate these results into language more transparent to physicists, so that experts in Monte Carlo calculations, high and low temperature expansions, and various other methods, can use them. We shall pay special attention to the interfacial tension ǫr between the k state and the k −r state. By examining the ground states, it is seen that the integrable line ends at a superwetting point, on which the relation ǫr = r ǫ1 is satisfied, so that it is energetically neutral to have one interface or more. We present also some partial results on the meaning of the integrable line for low temperatures where it lives in the non-wet regime. We make Baxter’s exact results more explicit for the symmetric case. By performing a Bethe Ansatz calculation with open boundary conditions we confirm a dilogarithm identity for the low-temperature expansion which may be new. We propose a new model for numerical studies. This model has only two variables and exhibits commensurate and incommensurate phase transitions and wetting transitions near zero temperature. It appears to be not integrable, except at one point, and at each temperature there is a point, where it is almost identical with the integrable chiral Potts model. KEY WORDS: Chiral Potts model; chiral clock model; star-triangle equations; Yang-Baxter equations; interfacial tension; wetting; superwetting;
First, an algebraic criterion for integrability is discussed -the so-called `superintegrability'- and some results on the classification of superintegrable quantum spin Hamiltonians based on sl(2) are obtained. Next, the massive phases of the Z_n-chiral Potts quantum spin chain (a model that violates parity) are studied in detail. It is shown that the excitation spectrum of the massive high-temperature phase can be explained in terms of n-1 fundamental quasiparticles. We compute correlation functions from a perturbative and numerical evaluation of the groundstate for the Z_3-chain. In addition to an exponential decay we observe an oscillating contribution. The oscillation length seems to be related to the asymmetry of the dispersion relations. We show that this relation is exact at special values of the parameters for general Z_n using a form factor expansion. Finally, we discuss several aspects of extended conformal algebras (W-algebras). We observe an analogy between boundary conditions for Z_n-spin chains and W-algebras and then turn to statements about the structure of W-algebras. In particular, we briefly summarize results on unifying structures present in the space of all quantum W-algebras.
We prove an exact finite-volume symmetry formula for two-point functions in the periodic N-state superintegrable chiral Potts spin chain. We show that, for every chain length L and every simultaneous eigenvector of the Hamiltonian and the one-site translation operator, the correlations satisfy ⟨Z0rZR†r⟩∗=⟨Z0rZL−R†r⟩ for 1⩽r⩽N−1. Hence, whenever L is even, the midpoint correlation ⟨Z0rZL/2†r⟩ is real. Then we generalise the three-state chain case to arbitrary N and to every translation eigensector. This resolves a conjecture of Fabricius and McCoy.