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arXiv:hep-th/9808150 · Journal of Physics A Mathematical and General

Classical and quantum integrable systems with boundaries

Yi-Xin Chen, Xudong Luo, Ke Wu

Published Jan 1, 1999• 2 citations
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Abstract

We study two-dimensional classically integrable field theory with independent boundary conditions at each end, and obtain three possible generating functions for integrals of motion when this model is an ultralocal one. Classically integrable boundary conditions can be found when solving boundary equations. In the quantum case, we also find that the unitarity condition of the quantum R -matrix is sufficient to construct commutative quantities with boundaries, and its reflection equations are obtained.

DOI
10.1088/0305-4470/32/5/008

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We study two-dimensional classically integrable field theory with independent boundary conditions at each end, and obtain three possible generating functions for integrals of motion when this model is an ultralocal one. Classically integrable boundary conditions can be found when solving boundary equations. In the quantum case, we also find that the unitarity condition of the quantum R -matrix is sufficient to construct commutative quantities with boundaries, and its reflection equations are obtained.
A simple relation between inhomogeneous transfer matrices and boundary quantum Knizhnik-Zamolodchikov (KZ) equations is exhibited for quantum integrable systems with reflecting boundary conditions, analogous to an observation by Gaudin for periodic systems. Thus, the boundary quantum KZ equations receive a new motivation. We also derive the commutativity of Sklyanin’s boundary transfer matrices by merely imposing appropriate reflection equations, in particular without using the conditions of crossing symmetry and unitarity of the R-matrix.
Abstract We reconcile the Hamiltonian formalism and the zero curvature representation in the approach to integrable boundary conditions for a classical integrable system in 1 + 1 space-time dimensions. We start from an ultralocal Poisson algebra involving a Lax matrix and two (dynamical) boundary matrices. Sklyanin’s formula for the double-row transfer matrix is used to derive Hamilton’s equations of motion for both the Lax matrix and the boundary matrices in the form of zero curvature equations. A key ingredient of the method is a boundary version of the Semenov-Tian-Shansky formula for the generating function of the time-part of a Lax pair. The procedure is illustrated on the finite Toda chain for which we derive Lax pairs of size for previously known Hamiltonians of type BC N and D N corresponding to constant and dynamical boundary matrices respectively.
We reconcile the Hamiltonian formalism and the zero curvature representation in the approach to integrable boundary conditions for a classical integrable system in 1 + 1 space-time dimensions. We start from an ultralocal Poisson algebra involving a Lax matrix and two (dynamical) boundary matrices. Sklyanin's formula for the double-row transfer matrix is used to derive Hamilton's equations of motion for both the Lax matrix and the boundary matrices in the form of zero curvature equations. A key ingredient of the method is a boundary version of the Semenov-Tian-Shansky formula for the generating function of the time-part of a Lax pair. The procedure is illustrated on the finite Toda chain for which we derive Lax pairs of size for previously known Hamiltonians of type BC N and D N corresponding to constant and dynamical boundary matrices respectively.
Some results for commuting local integrals of motion for free bosonic theories are presented, which can be applied in construction of integrable boundary states. We consider a particular model of two-dimensional quantum field theory on a disk, whose bulk dynamics is that of a two-component free massless Bose field X = (X, Y), and interaction occurs at the boundary, where the boundary values (XB, YB) are constrained to special curve—the “paperclip brane”. The interaction breaks conformal invariance, but we argue that it preserves integrability. We propose exact expression for the disk partition function (and more general overlap amplitudes ⟨P| B⟩ of the boundary state with all primary states) in terms of solutions of certain ordinary linear differential equations. Usable program code for calculation of commuting integrals of motion is also introduced.
Some special solutions to the reflection equation are considered. These boundary matrices are defined on the common quantum space with the other operators in the chain. The relations with the Drinfeld twist are discussed. PACS: 02.90.+p, 03.20.+i,03.65.Fd, 11.30.-j 0 1 On a covariance property of the reflection equation Let the operator-valued function R(u) : C → Aut(V ⊗ V) be a solution to the quantum Yang-Baxter equation [1] in a finite-dimensional linear space V. Let us connect with a given matrix R(u) two associative algebras TR and UR generated by noncommutative entries of the square matrices T(u) and K(u) satisfying the fundamental commutator relation [1, 2] or the reflection equation [3, 4] R12(u − v) 1