619 research outputs found
Excited state TBA and functional relations in spinless Fermion model
The excited state thermodynamic Bethe ansatz (TBA) equations for the spinless
Fermion model are presented by the quantum transfer matrix (QTM) approach. We
introduce a more general family called T-functions and explore functional
relations among them (T-system) and their certain combinations (Y-system).
{}From their analytical property, we derive a closed set of non-linear integral
equations which characterize the correlation length of at
any finite temperatures. Solving these equations numerically, we explicitly
determine the correlation length, which coincides with earlier results with
high accuracy.Comment: 4 page
Commuting quantum transfer matrix approach to intrinsic Fermion system: Correlation length of a spinless Fermion model
The quantum transfer matrix (QTM) approach to integrable lattice Fermion
systems is presented. As a simple case we treat the spinless Fermion model with
repulsive interaction in critical regime. We derive a set of non-linear
integral equations which characterize the free energy and the correlation
length of for arbitrary particle density at any finite
temperatures. The correlation length is determined by solving the integral
equations numerically. Especially in low temperature limit this result agrees
with the prediction from conformal field theory (CFT) with high accuracy.Comment: 17 page
An exploratory study of heavy domain wall fermions on the lattice
We report on an exploratory study of domain wall fermions (DWF) as a lattice
regularisation for heavy quarks. Within the framework of quenched QCD with the
tree-level improved Symanzik gauge action we identify the DWF parameters which
minimise discretisation effects. We find the corresponding effective 4
overlap operator to be exponentially local, independent of the quark mass. We
determine a maximum bare heavy quark mass of , below which the
approximate chiral symmetry and O(a)-improvement of DWF are sustained. This
threshold appears to be largely independent of the lattice spacing. Based on
these findings, we carried out a detailed scaling study for the heavy-strange
meson dispersion relation and decay constant on four ensembles with lattice
spacings in the range . We observe very mild
scaling towards the continuum limit. Our findings establish a sound basis for
heavy DWF in dynamical simulations of lattice QCD with relevance to Standard
Model phenomenology.Comment: 23 pages, 8 figure
Completeness of ``Good'' Bethe Ansatz Solutions of a Quantum Group Invariant Heisenberg Model
The -quantum group invariant spin 1/2 XXZ-Heisenberg model with open
boundary conditions is investigated by means of the Bethe ansatz. As is well
known, quantum groups for equal to a root of unity possess a finite number
of ``good'' representations with non-zero q-dimension and ``bad'' ones with
vanishing q-dimension. Correspondingly, the state space of an invariant
Heisenberg chain decomposes into ``good'' and ``bad'' states. A ``good'' state
may be described by a path of only ``good'' representations. It is shown that
the ``good'' states are given by all ``good'' Bethe ansatz solutions with roots
restricted to the first periodicity strip, i.e. only positive parity strings
(in the language of Takahashi) are allowed. Applying Bethe's string counting
technique completeness of the ``good'' Bethe states is proven, i.e. the same
number of states is found as the number of all restricted path's on the
-Bratteli diagram. It is the first time that a ``completeness" proof
for an anisotropic quantum invariant reduced Heisenberg model is performed.Comment: LaTeX file with LaTeX figures, 24 pages, 1 PiCTeX figur
Bayesian inference for form-factor fits regulated by unitarity and analyticity
We propose a model-independent framework for fitting hadronic form-factor
data, which is often only available at discrete kinematical points, using
parameterisations based on to unitarity and analyticity. In this novel approach
the latter two properties of quantum-field theory regulate the ill-posed
fitting problem and allow model-independent predictions over the entire
physical range. Kinematical constraints, for example for the vector and scalar
form factors in semileptonic meson decays, can be imposed exactly. The core
formulae are straight-forward to implement with standard math libraries. We
take account of a generalisation of the original Boyd~Grinstein~Lebed (BGL)
unitarity constraint for form factors and demonstrate our method for the
exclusive semileptonic decay , for which we make a number of
phenomenologically relevant predictions, including the CKM matrix element
.Comment: 45 pages, 8 figures, references added, typos fixe
Relativistic diffusive motion in random electromagnetic fields
We show that the relativistic dynamics in a Gaussian random electromagnetic
field can be approximated by the relativistic diffusion of Schay and Dudley.
Lorentz invariant dynamics in the proper time leads to the diffusion in the
proper time. The dynamics in the laboratory time gives the diffusive transport
equation corresponding to the Juettner equilibrium at the inverse temperature
\beta^{-1}=mc^{2}. The diffusion constant is expressed by the field strength
correlation function (Kubo's formula).Comment: the version published in JP
The q-deformed Bose gas: Integrability and thermodynamics
We investigate the exact solution of the q-deformed one-dimensional Bose gas
to derive all integrals of motion and their corresponding eigenvalues. As an
application, the thermodynamics is given and compared to an effective field
theory at low temperatures.Comment: 10 pages, 6 figure
Integrability of quantum chains: theory and applications to the spin-1/2 chain
In this contribution we review the theory of integrability of quantum systems
in one spatial dimension. We introduce the basic concepts such as the
Yang-Baxter equation, commuting currents, and the algebraic Bethe ansatz. Quite
extensively we present the treatment of integrable quantum systems at finite
temperature on the basis of a lattice path integral formulation and a suitable
transfer matrix approach (quantum transfer matrix). The general method is
carried out for the seminal model of the spin-1/2 chain for which
thermodynamic properties like specific heat, magnetic susceptibility and the
finite temperature Drude weight of the thermal conductivity are derived
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