1,137 research outputs found

### Effective potentials and kink spectra in non-integrable perturbed conformal field theories

We analyze the evolution of the effective potential and the particle spectrum
of two-parameter families of non-integrable quantum field theories. These
theories are defined by deformations of conformal minimal models M_m by using
the operators Phi_{1,3}, Phi_{1,2} and Phi_{2,1}. This study extends to all
minimal models the analysis previously done for the classes of universality of
the Ising, the Tricritical Ising and the RSOS models. We establish the symmetry
and the duality properties of the various models also identifying the limiting
theories that emerge when m goes to infinity.Comment: 30 pages, pdflatex,17 figures

### Excited state TBA and renormalized TCSA in the scaling Potts model

We consider the field theory describing the scaling limit of the Potts
quantum spin chain using a combination of two approaches. The first is the
renormalized truncated conformal space approach (TCSA), while the second one is
a new thermodynamic Bethe Ansatz (TBA) system for the excited state spectrum in
finite volume. For the TCSA we investigate and clarify several aspects of the
renormalization procedure and counter term construction. The TBA system is
first verified by comparing its ultraviolet limit to conformal field theory and
the infrared limit to exact S-matrix predictions. We then show that the TBA and
the renormalized TCSA match each other to a very high precision for a large
range of the volume parameter, providing both a further verification of the TBA
system and a demonstration of the efficiency of the TCSA renormalization
procedure. We also discuss the lessons learned from our results concerning
recent developments regarding the low-energy scattering of quasi-particles in
the quantum Potts spin chain.Comment: 39 pages, 5 eps figures. v2: reference added. v3: several misprints
corrected, and an important step in the derivation of counter terms (in
section 3.4.1) is explained in more detai

### Confinement in the q-state Potts model: an RG-TCSA study

In the ferromagnetic phase of the q-state Potts model, switching on an
external magnetic field induces confinement of the domain wall excitations. For
the Ising model (q = 2) the spectrum consists of kink-antikink states which are
the analogues of mesonic states in QCD, while for q = 3, depending on the sign
of the field, the spectrum may also contain three-kink bound states which are
the analogues of the baryons. In recent years the resulting "hadron" spectrum
was described using several different approaches, such as quantum mechanics in
the confining linear potential, WKB methods and also the Bethe-Salpeter
equation. Here we compare the available predictions to numerical results from
renormalization group improved truncated conformal space approach (RG-TCSA).
While mesonic states in the Ising model have already been considered in a
different truncated Hamiltonian approach, this is the first time that a
precision numerical study is performed for the 3-state Potts model. We find
that the semiclassical approach provides a very accurate description for the
mesonic spectrum in all the parameter regime for weak magnetic field, while the
low-energy expansion from the Bethe-Salpeter equation is only valid for very
weak fields where it gives a slight improvement over the semiclassical results.
In addition, we confirm the validity of the recent predictions for the baryon
spectrum obtained from solving the quantum mechanical three-body problem.Comment: 22 pages, pdflatex source with pdf figures. Version 2: references
added, introduction change

### Boundary reduction formula

An asymptotic theory is developed for general non-integrable boundary quantum
field theory in 1+1 dimensions based on the Langrangean description. Reflection
matrices are defined to connect asymptotic states and are shown to be related
to the Green functions via the boundary reduction formula derived. The
definition of the $R$-matrix for integrable theories due to Ghoshal and
Zamolodchikov and the one used in the perturbative approaches are shown to be
related.Comment: 12 pages, Latex2e file with 5 eps figures, two Appendices about the
boundary Feynman rules and the structure of the two point functions are adde

### Overlaps after quantum quenches in the sine-Gordon model

We present a numerical computation of overlaps in mass quenches in
sine-Gordon quantum field theory using truncated conformal space approach
(TCSA). To improve the cut-off dependence of the method, we use a novel running
coupling definition which has a general applicability in free boson TCSA. The
numerical results are used to confirm the validity of a previously proposed
analytical Ansatz for the initial state in the sinh-Gordon quench.Comment: 13 pages, 4 pdf figure

### Quasi-particle spectrum and entanglement generation after a quench in the quantum Potts spin chain

Recently, a non-trivial relation between the quasi-particle spectrum and
entanglement entropy production was discovered in non-integrable quenches in
the paramagnetic Ising quantum spin chain. Here we study the dynamics of
analogous quenches in the quantum Potts spin chain. Tuning the parameters of
the system, we observe a sudden increase in the entanglement production rate,
which is shown to be related to the appearance of new quasiparticle excitations
in the post-quench spectrum. Our results demonstrate the generality of the
effect and support its interpretation as the non-equilibrium version of the
well-known Gibbs paradox related to mixing entropy which appears in systems
with a non-trivial quasi-particle spectrum.Comment: 15 pages, pdflatex, 30 pdf figures. v2: reformatted, 22 pages, typos
correcte

### A2 Toda theory in reduced WZNW framework and the representations of the W algebra

Using the reduced WZNW formulation we analyse the classical $W$ orbit content
of the space of classical solutions of the $A_2$ Toda theory. We define the
quantized Toda field as a periodic primary field of the $W$ algebra satisfying
the quantized equations of motion. We show that this local operator can be
constructed consistently only in a Hilbert space consisting of the
representations corresponding to the minimal models of the $W$ algebra.Comment: 38 page

### On the relation between Phi(1,2) and Phi(1,5) perturbed minimal models

We consider the RSOS S-matrices of the Phi(1,5) perturbed minimal models
which have recently been found in the companion paper [hep-th/9604098]. These
S-matrices have some interesting properties, in particular, unitarity may be
broken in a stronger sense than seen before, while one of the three classes of
Phi(1,5) perturbations (to be described) shares the same Thermodynamic Bethe
Ansatz as a related Phi(1,2) perturbation. We test these new S-matrices by the
standard Truncated Conformal Space method, and further observe that in some
cases the BA equations for two particle energy levels may be continued to
complex rapidity to describe (a) single particle excitations and (b) complex
eigenvalues of the Hamiltonian corresponding to non-unitary S-matrix elements.
We make some comments on identities between characters in the two related
models following from the fact that the two perturbed theories share the same
breather sector.Comment: LaTeX, 23 pages, 12 figures. Substantial revision of introductory
section, new discussion of complex eigenvalues and non-unitary S-matrice

### Initial states in integrable quantum field theory quenches from an integral equation hierarchy

We consider the problem of determining the initial state of integrable
quantum field theory quenches in terms of the post-quench eigenstates. The
corresponding overlaps are a fundamental input to most exact methods to treat
integrable quantum quenches. We construct and examine an infinite integral
equation hierarchy based on the form factor bootstrap, proposed earlier as a
set of conditions deter- mining the overlaps. Using quenches of the mass and
interaction in Sinh-Gordon theory as a concrete example, we present theoretical
arguments that the state has the squeezed coherent form expected for integrable
quenches, and supporting an Ansatz for the solution of the hierarchy. Moreover
we also develop an iterative method to solve numerically the lowest equation of
the hierarchy. The iterative solution along with extensive numerical checks
performed using the next equation of the hierarchy provide a strong numerical
evidence that the proposed Ansatz gives a very good approximation for the
solution.Comment: 36 pages, pdflatex file, 11 pdf figures. v2: revised version,
accepted for publicatio

### Finite temperature expectation values of boundary operators

A conjecture is presented for the thermal one-point function of
boundary operators in integrable boundary quantum field theories in
terms of form factors. It is expected to have applications in studying
boundary critical phenomena and boundary flows, which are relevant in
the context of condensed matter and string theory. The conjectured
formula is verified by a low-temperature expansion developed using
finite size techniques, which can also be used to evaluate higher point
functions both in the bulk and on the boundary. (c) 2008 Elsevier B.V.
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