Commensurate-incommensurate phase transition in one-dimensional quantum sine-Gordon model based on a lattice massive thirring model

The commensurate-incommensurate (C-IC) phase transition in the one dimensional quantum sine-Gordon model at zero temperature is exactly solved with the use of the Bethe ansatz technique for the lattice massive Thirring model. The energy difference between C and IC phases is derived based on the same ground state which is valid in the whole parameter region. It is due to the fact that there is no change in the ground state of the lattice massive Thirring model even in the strongly repulsive region in contrast to the continuum massive Thirring model even in the strongly repulsive region in contrast to the continuum massive Thirring model. It is proved in the whole parameter region that the IC phase can be realized with the soliton density proportional to (E _s : formation energy of soliton), whenE _s becomes negative.     

Integrable lattice version of the massive thirring model and its linearization

A linear integral equation is proposed, yielding an exact linearization of a discretized version of the classical massive Thirring model on a two-dimensional lattice.     

A local and integrable lattice regularization of the massive Thirring model

The light-cone lattice approach to the massive Thirring model is reformulated using a local and integrable lattice hamiltonian written in terms of discrete Fermi fields. Several subtle points concerning boundary conditions, normal ordering, continuum limit, finite renormalizations and decoupling of fermion doublers are elucidated. The relations connecting the six-vertex anisotropy and the various coupling constants of the continuum are analyzed in detail.     

Ice models and a lattice version of the Dirac equation

We study ice models as possible realizations for lattice versions of the Dirac equation. The starting point of this analysis is the close connection between the two dimensional ice model of Lieb and the Thirring model of massive fermions in (1+1) dimensions.Dedicated to B. Mühlschlegel on the occasion of his 60th birthdaySupported by Deutsche Forschungsgemeinschaft     

The massive thirring model as continuum limit of the Heisenberg model

The continuum limit of the lattice fermion version of the anisotropic spin-1/2 Heisenberg chain is reconsidered. It is shown that certain matrix elements of the Heisenberg Hamiltonian converge towards corresponding matrix elements of a massive Thirring model as previously suggested by Luther and Peschel. However, the result is only to first order consistent with the exactly known spectral and critical properties of the two models. Going beyond previous results in addition to the coupling constant of the massive Thirring model the kinetic energy coefficient comes out correctly to the first order of the lattice fermion interaction, too. Emphasizing the role of the underlying Hilbert spaces the discrepancy in higher orders is explained.Work performed within the research program of the Sonderforschungsbereich 125 Aachen, Jülich, Köln     

The Thirring interaction in the two-dimensional axial–current–pseudoscalar derivative coupling model

We reexamine the two-dimensional model of massive fermions interacting with a massless pseudoscalar field via axial-current derivative coupling. The hidden Thirring interaction in the axial-derivative coupling model is exhibited compactly by performing a canonical field transformation on the Bose field algebra and the model is mapped into the Thirring model with an additional vector–current–scalar derivative interaction (Schroer–Thirring model). The Fermi field operator is rewritten in terms of the Mandelstam soliton operator coupled to a free massless scalar field. The charge sectors of the axial-derivative model are mapped into the charge sectors of the massive Thirring model. The complete bosonized version of the model is presented. The bosonized composite operators of the quantum Hamiltonian are obtained as the leading operators in the Wilson short distance expansions.     

Free Massive Fermions¶Inside the Quantum Discrete sine-Gordon Model

We extend the notion of space shifts introduced in [FV3] for certain quantum light cone lattice equations of sine-Gordon type at root of unity (e.g. [FV1,FV2,BKP,BBR]). As a result, we obtain a compatibility equation for the roots of central elements within the algebra of observables (also called current algebra). The equation, which is obtained by exponentiating these roots, is exactly the evolution equation for the?“classical background” as described in [BBR]. As an application for the introduced constructions, we derive a one to one correspondence between a special case of the quantum light cone lattice equations of sine-Gordon type and free massive fermions on a lattice, as a special case of the lattice Thirring model constructed in [DV]. Received: 2 December 1996 / Accepted: 19 January 1999     

Interacting fermions on a random lattice

We extend previous work on the properties of the Dirac lagrangian on two-dimensional random lattices to the case where interaction terms are included. Although for free fermions the chiral symmetry of the doubles is spontaneously broken by their interaction with the lattice and they decouple from long-distance physics, our results in this paper show that all is undone by quantum corrections in an interacting field theory and that the end result is very similar to what is found with Wilson fermions. Two field-theoretical models with interacting fermions are studied by perturbation expansion in the field theory coupling constant. These are a model with one fermion and one boson species interacting via a scalar Yukawa coupling and the massive Thirring model. It is shown that on the random lattice ultraviolet finite diagrams and finite parts of ultraviolet divergent diagrams have the correct continuum limit. Ultraviolet divergent parts can be removed by the same renormalisation procedure as in the continuum, but do not exhibit the same dependence on the lagrangian mass. In the case of the massive Thirring model this causes a fermion mass correction of order the cut-off scale, which breaks the chiral symmetry of the remaining light fermion; there is consequently a fine-tuning problem. In the context of the same model we discuss the effect of the Goldstone boson associated with the spontaneous breakdown of the chiral symmetry of the doubles on two-dimensional models with vector couplings.     

On the scaling limit of the 1D Hubbard model at half-filling

The dispersion relations and S-matrix of the one-dimensional Hubbard model at half-filling are onsidered in a certain scaling limit. (In the process we derive a useful small-coupling expansion of the exact lattice dispersion relations.) The resulting scattering theory is consistently identified as that of the SU(2) chiral-invariant Thirring (or Gross-Neveu) field theory, containing both massive and massless sectors.     

On the equivalence between sine-Gordon model and Thirring model in the chirally broken phase of the Thirring model

We investigate the equivalence between Thirring model and sine-Gordon model in the chirally broken phase of the Thirring model. This is unlike all other available approaches where the fermion fields of the Thirring model were quantized in the chiral symmetric phase. In the path integral approach we show that the bosonized version of the massless Thirring model is described by a quantum field theory of a massless scalar field and exactly solvable, and the massive Thirring model bosonizes to the sine-Gordon model with a new relation between the coupling constants. We show that the non-perturbative vacuum of the chirally broken phase in the massless Thirring model can be described in complete analogy with the BCS ground state of superconductivity. The Mermin–Wagner theorem and Coleman's statement concerning the absence of Goldstone bosons in the 1+1-dimensional quantum field theories are discussed. We investigate the current algebra in the massless Thirring model and give a new value of the Schwinger term. We show that the topological current in the sine-Gordon model coincides with the Noether current responsible for the conservation of the fermion number in the Thirring model. This allows one to identify the topological charge in the sine-Gordon model with the fermion number. Received: 16 December 2000 / Revised version: 23 April 2001 / Published online: 13 June 2001     

Strong coupling expansion in the massive Thirring model

A strong coupling expansion of the Green functions in the massive Thirring model is formulated. Expressions obtained for the fundamental fermion mass and theβ function agree with the known qualitative features of these physical quantities.     

On relativistic-invariant formulation of the inverse scattering transform method

A manifestly relativistic-invariant formulation of the method of inverse scattering transform for relativistic-invariant equations is proposed. The sine-Gordon model and the massive Thirring model are considered.     

The derivative nonlinear Schrödinger equation and the massive Thirring model

The linearization and Bäcklund transformations are obtained for a class of nonlinear partial differential equations, which contains the derivative nonlinear Schrödinger equation and the equations for the massive Thirring model     

Orbital Stability of Dirac Solitons

We prove H ¹ orbital stability of Dirac solitons in the integrable massive Thirring model by working with an additional conserved quantity which complements Hamiltonian, momentum and charge functionals of the general nonlinear Dirac equations. We also derive a global bound on the H ¹ norm of the L ²-small solutions of the massive Thirring model.     

Conserved currents in the massive thirring model

The existence of an infinite set of conserved currents in the massive Thirring model is discussed. The first four nontrivial currents are given explicitely.     

Exact form factors in integrable quantum field theories: the sine-Gordon model (II)

A general model independent approach using the ‘off-shell Bethe Ansatz’ is presented to obtain an integral representation of generalized form factors. The general techniques are applied to the quantum sine-Gordon model alias the massive Thirring model. Exact expressions of all matrix elements are obtained for several local operators. In particular soliton form factors of charge-less operators as for example all higher currents are investigated. It turns out that the various local operators correspond to specific scalar functions called p-functions. The identification of the local operators is performed. In particular the exact results are checked with Feynman graph expansion and full agreement is found. Furthermore all eigenvalues of the infinitely many conserved charges are calculated and the results agree with what is expected from the classical case. Within the frame work of integrable quantum field theories a general model independent ‘crossing’ formula is derived. Furthermore the ‘bound state intertwiners’ are introduced and the bound state form factors are investigated. The general results are again applied to the sine-Gordon model. The integrations are performed and in particular for the lowest breathers a simple formula for generalized form factors is obtained.     

Form factors of soliton-creating operators in the sine-Gordon model

We propose explicit expressions for the form factors, including their normalization constants, of topologically charged (or soliton-creating) operators in the sine-Gordon model. The normalization constants, which constitute the main content of our proposal, allow one to find exact relations between the short- and long-distance asymptotics of the correlation functions. We make predictions concerning asymptotics of fermion correlation functions in the massive Thirring model, SU(2)–Thirring model with anisotropy, and in the half-filled Hubbard chain.     

Exact two-particle S-matrix of quantum sine-Gordon solitons

The exact and explicit formulas for the quantumS-matrix elements of the soliton-antisoliton scattering which satisfy unitarity and crossing conditions and have correct analytical properties are constructed. ThisS-matrix is in agreement with the massive Thirring model perturbation theory and with the semiclassical sine-Gordon results.     

Particle number conservation in the massive thirring model

We computed pair-production and nontrivial three-particle scattering amplitudes of the massive Thirring model in one loop approximation. They are found to be zero.     

On the inverse scattering method for the classical massive thirring model with anticommuting variables

The inverse scattering method is applied to the classical Grassman-valued massive Thirring model. In the framework of the method the existence of an infinity of both local and non-local conservation laws is established. It is shown that there are no simple solitons in the model.