Path-integral formulation of chiral invariant fermion models in two dimensions

We study the Thirring and chiral-invariant Gross-Neveu (CGN) models using the functional integral method. By introducing an auxiliary vector field we disclose a relation with two-dimensional gauge theories coupled to fermions and then extend a technique based on a chiral change in the functional variables to study purely fermionic models.We obtain the exact Klaiber solution for the massless Thirring model (for spin $\text{1}\text{2}$) in a very simple way and we then extend our technique to investigate the CGN model. We show the factorization of a free fermionic part at the level of Green functions on very general grounds. We then impose certain restrictions on the behavior of the fields — which render our treatment exact only in the zero winding number sector, but allow the computation of the U(1) part of the CGN Green functions exactly, showing, in particular, its complete decoupling from the color part and the almost long-range order behaviour in the infrared region.In our approach, the non-triviality of the jacobian arising from the chiral transformation — directly related to the topological density and the axial anomaly — appears to be crucial for the functional integral treatment of these models.     

Two-dimensional quantum field theories containing a massless scalar field

The following new findings are briefly reported:

1. A consistent quantum theory can be formulated for a free massless scalar field in two-dimensional spacetime.
2. Satisfactory operator solutions in terms of asymptotic fields can be constructed in the Thirring and Schwinger models.
3. Gauge invariance is spontaneously broken in the Thirring model as well as in the Schwinger model.

     

Unconventional spin solutions of the Schwinger and Thirring models

A satisfactory operator solution of the Schwinger-Thirring model is found which ase→0 org→0 tends respectively to the operator solution of the Thirring or the Schwinger model. We also propose the general solutions of the Schwinger-Thirring model which can be associated with the solution of the Thirring model with unconventional statistics. In particular our method allows for a generalization of the Schwinger model for arbitrary spins giving rise to a new solution with the “photon” mass dependent ons. The following consequences for a bosonization procedure is also described.

     

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.     

Use of some fermion field identities for bosonisation of U(n) thirring and Schwinger models

A set of identities involving triple products of free fermion fields belonging to the fundamental representation of U(n) is established. These would give a direct bosonised form of U(n) massless as well as massive Thirring model for \(g_\upsilon = - \frac{{4\pi }}{{n + 1}}\) . The identities are also shown to exist for fields whose leading operator product expansion is same as that of free fermion fields. This would then give us an exactly solvable bosonised form of U(n) Schwinger model.     

On global solutions of the Maxwell-Dirac equations

We prove, for the Maxwell-Dirac equations in 1+3 dimensions, that modified wave operators exist on a domain of small entire test functions of exponential type and that the Cauchy problem, inR ⁺×R ³, has a unique solution for each initial condition (att=0) which is in the image of the wave operator. The modification of the wave operator, which eliminates infrared divergences, is given by approximate solutions of the Hamilton-Jacobi equation, for a relativistic electron in an electromagnetic potential. The modified wave operator linearizes the Maxwell-Dirac equations to their linear part.Dedicated to Walter Thirring on his 60^th birthdayThis work is dedicated to Walter Thirring upon the occasion of his sixtieth birthday with appreciation and friendship     

The Algebraic Structure of the Thirring Model

We summarize the representation theory of the group SU(1,1) as needed for the massless Thirring model. Representations of the current operator algebra are given taking account of conformal covariance. The conformal covariance transformation behaviour of the Thirring field is investigated. The Haag-Araki-Kastler observable algebra of the Thirring field is reconstructed from the Wightman theory of this model.     

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     

Operator ordering schemes and covariant path integrals of quantum and stochastic processes in Curved space

A method is given for the derivation of covariant path integral solutions of quantum and stochastic processes in curved space.The correspondence between operator ordering schemes and ordinary functions in phase space is studied and applied to the explicit construction of a class of equivalent lattice representations of path integrals. It is shown that this class is uniquely related to a covariant functional integral. Some arguments forR/12 as the quantum mechanical curvature potential are given. Simple rules for nonlinear point transformations are stated. The connection with previous works is discussed.     

THE NONABELIAN BOSONIZATION OF FERMION FIELDS IN (1+1) DIMENSIONS BY PATH INTEGRAL METHOD

Using the path integral method for handling the anomaly problem under the comoving representation,we present a unified scheme for deriving the bononization of fermion fields in (1+1) dimensions.The massless Thirring model with an external electric field,and the Gross-Neveu model with internal SU(N) symmetry,as two examples for abelian and nonabelian bosonization,are discussed repectively in some detail.     

Conformal invariance of quantum fields in two-dimensional space-time

Our investigations of conformal invariance are based on the theory of analytic representations of the conformal group and its universal covering group. With its help the action of the conformal group on free massless fields, Greenberg fields, Wick products of these fields, and the Thirring fields is studied. In this context we find an infinite set of new operator solutions for the Thirring model that are all equivalent to each other. Explicit constructions of the nonlocal special conformal transformations of all these fields are given.     

黑洞背景下费米物质能量密度涨落的计算

应用泛函积分方法推导了量子Thirring模型中的传播子和有效势,计算了二维点物质黑洞和dilaton黑洞模型中费米物质的能量密度涨落,在相同的物理条件下,发现dilaton黑洞外费米物质的能量密度涨较大.     

Integrability and the variational formulation of non‐conservative mechanical systems

It is shown that one can obtain canonically‐defined dynamical equations for non‐conservative mechanical systems by starting with a first variation functional, instead of an action functional, and finding their zeroes. The kernel of the first variation functional, as an integral functional, is a 1‐form on the manifold of kinematical states, which then represents the dynamical state of the system. If the 1‐form is exact then the first variation functional is associated with the first variation of an action functional in the usual manner. The dynamical equations then follow from the vanishing of the dual of the Spencer operator that acts on the dynamical state. This operator, in turn, relates to the integrability of the kinematical states. The method is applied to the modeling of damped oscillators.     

Bosonization and generalized Mandelstam soliton operators

The generalized massive Thirring model (GMT) with three fermion species is bosonized in the context of the functional integral and operator formulations and shown to be equivalent to a generalized sine-Gordon model (GSG) with three interacting soliton species. The generalized Mandelstam soliton operators are constructed and the fermion-boson mapping is established through a set of generalized bosonization rules in a quotient positive-definite Hilbert space of states. Each fermion species is mapped to its corresponding soliton in the spirit of particle/soliton duality of Abelian bosonization. In the semi-classical limit one recovers the so-called SU(3) affine Toda model coupled to matter fields (ATM) from which the classical GSG and GMT models were recently derived in the literature. The intermediate ATM-like effective action possesses some spinors resembling the higher grading fields of the ATM theory which have non-zero chirality. These fields are shown to disappear from the physical spectrum, thus providing a bag-model-like confinement mechanism and leading to the appearance of massive fermions (solitons). The ordinary MT/SG duality turns out to be related to each SU(2) sub-group. The higher rank Lie algebra extension is also discussed.Received: 6 July 2004, Published online: 2 September 2004     

Some Classes of Solutions to the Toda Lattice Hierarchy

We apply an analogue of the Zakharov-Shabat dressing method to obtain infinite matrix solutions to the Toda lattice hierarchy. Using an operator transformation we convert some of these into solutions in terms of integral operators and Fredholm determinants. Others are converted into a class of operator solutions to the l-periodic Toda hierarchy. Received: 12 March 1996 / Accepted: 26 September 1996     

The exact equation of motion for a two level system. Zubarev like approach

A simple model, one spinS=1/2 interacting with an alternating transverse field and with a single mode of a boson field, treated as an open system, is rigorously investigated. An approach based on the Zubarev method is applied. An integro-differential equation for a mean value of the Zeeman operator is derived. Kernels of this equation are defined as solutions of some functional (integral) equations. A particular case, known as the Jaynes-Cummings model in quantum optics, is considered. The Markovian limit of the integro-differential equation for the Jaynes-Cummings model leads to a simple relaxation equation.Supported in part by the Polish Academy of Sciences.The author would like to thank Prof. A. Pawlikowski for his continual interest in the present work and useful comments and discussions. The author is also indebted to Dr. E. Malec and Dr. J. Aksamit for their help during the preparation of this paper.     

Exactly Solvable Models and Spontaneous Symmetry Breaking

We study a few two-dimensional models with massless and massive fermions in the hamiltonian framework and in both conventional and light-front (LF) forms of field theory. The new ingredient is a modification of the canonical procedure by taking into account solutions of the operator field equations. After summarizing the main results for the derivative-coupling and the Thirring models, we briefly compare conventional and LF versions of the Federbush model including the massive current bosonization and a Bogoliubov transformation to diagonalize the Hamiltonian. Then we sketch an extension of our hamiltonian approach to the two-dimensional Nambu–Jona-Lasinio model and the Thirring-Wess model. Finally, we discuss the Schwinger model in a covariant gauge. In particular, we point out that the solution due to Lowenstein and Swieca implies the physical vacuum in terms of a coherent state of massive scalar field and suggest a new formulation of the model’s vacuum degeneracy.     

The conformal points of the generalized Thirring model II

In the large-N limit, conditions for the conformal invariance of the generalized Thirring model are derived, using two different approaches: the background field method and the hamiltonian method based on an operator algebra, and the agreement between them is established. A free field representation of the relevant algebra is presented, and the structure of the stress tensor in terms of free fields (and free currents) is studied in detail.