625 research outputs found
Exact calculation of thermodynamical quantities of the integrable t-J model
The specific heat and the compressibility for the integrable t-J model are
calculated showing Luttinger liquid behavior for low temperatures. A
Trotter-Suzuki mapping and the quantum transfer matrix approach are utilized.
Using an algebraic Bethe ansatz this method permits the exact calculation of
the free energy and related quantities. A set of just two non-linear integral
equations determining these quantities is studied for various particle
densities and temperatures. The structure of the specific heat is discussed in
terms of the elementary charge as well as spin excitations.Comment: 4 pages, 5 Postscript figures, uses epsf.sty and revtex, tar'ed,
gzip'ed and uuencode
On the efficiency of stochastic volume sources for the determination of light meson masses
We investigate the efficiency of single timeslice stochastic sources for the
calculation of light meson masses on the lattice as one varies the quark mass.
Simulations are carried out with Nf = 2 flavours of non-perturbatively O(a)
improved Wilson fermions for pion masses in the range of 450 - 760 MeV. Results
for pseudoscalar and vector meson two-point correlation functions computed
using stochastic as well as point sources are presented and compared. At fixed
computational cost the stochastic approach reduces the variance considerably in
the pseudoscalar channel for all simulated quark masses. The vector channel is
more affected by the intrinsic stochastic noise. In order to obtain stable
estimates of the statistical errors and a more pronounced plateau for the
effective vector meson mass, a relatively large number of stochastic sources
must be used.Comment: 18 pages, 6 figure
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
The decay constants and in the continuum limit of domain wall lattice QCD
We present results for the decay constants of the and mesons
computed in lattice QCD with dynamical flavours. The simulations are
based on RBC/UKQCD's domain wall ensembles with both physical and unphysical
light-quark masses and lattice spacings in the range 0.11--0.07fm. We
employ the domain wall discretisation for all valence quarks.
The results in the continuum limit are
and
and
.
Using these results in a Standard Model analysis we compute the predictions
and
for the
CKM matrix elements
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
The Hubbard chain at finite temperatures: ab initio calculations of Tomonaga-Luttinger liquid properties
We present a novel treatment of finite temperature properties of the
one-dimensional Hubbard model. Our approach is based on a Trotter-Suzuki
mapping utilizing Shastry's classical model and a subsequent investigation of
the quantum transfer matrix. We derive non-linear integral equations for three
auxiliary functions which have a clear physical interpretation of elementary
excitations of spin type and charge excitations in lower and upper Hubbard
bands. This allows for a transparent analytical study of certain limiting cases
as well as for precise numerical investigations. We present data for the
specific heat, magnetic and charge susceptibilities for various particle
densities and coupling strengths U. The structure exposed by these curves is
discussed in terms of the elementary charge and spin excitations. Special
emphasis is placed on the study of the low-temperature behavior within our ab
initio approach confirming the scaling predictions by Tomonaga-Luttinger liquid
theory. In addition we make contact with the ``dressed energy'' formalism
established for the analysis of ground state properties.Comment: 33 pages including 24 Postscript figure
Birth and destruction of collective oscillations in a network of two populations of coupled type 1 neurons
We study the macroscopic dynamics of large networks of excitable type 1
neurons composed of two populations interacting with disparate but symmetric
intra- and inter-population coupling strengths. This nonuniform coupling scheme
facilitates symmetric equilibria, where both populations display identical
firing activity, characterized by either quiescent or spiking behavior, or
asymmetric equilibria, where the firing activity of one population exhibits
quiescent but the other exhibits spiking behavior. Oscillations in the firing
rate are possible if neurons emit pulses with non-zero width but are otherwise
quenched. Here, we explore how collective oscillations emerge for two
statistically identical neuron populations in the limit of an infinite number
of neurons. A detailed analysis reveals how collective oscillations are born
and destroyed in various bifurcation scenarios and how they are organized
around higher codimension bifurcation points. Since both symmetric and
asymmetric equilibria display bistable behavior, a large configuration space
with steady and oscillatory behavior is available. Switching between
configurations of neural activity is relevant in functional processes such as
working memory and the onset of collective oscillations in motor control
Signal at subleading order in lattice HQET
We discuss the correlators in lattice HQET that are needed to go beyond the
static theory. Based on our implementation in the Schr\"odinger functional we
focus on their signal-to-noise ratios and check that a reasonable statistical
precision can be reached in quantities like and .Comment: 3 pages, Lattice2004(heavy), v2: corrected definition of X^{kin/spin
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