424 research outputs found
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
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
Cell-cell communication mediated by the CAR subgroup of immunoglobulin cell adhesion molecules in health and disease
The immunoglobulin superfamily represents a diverse set of cell-cell contact proteins and includes well-studied members such as NCAM1, DSCAM, L1 or the contactins which are strongly expressed in the nervous system. In this review we put our focus on the biological function of a less understood subgroup of Ig-like proteins composed of CAR (coxsackievirus and adenovirus receptor), CLMP (CAR-like membrane protein) and BT-IgSF (brain and testis specific immunoglobulin superfamily). The CAR-related proteins are type I transmembrane proteins containing an N-terminal variable (V-type) and a membrane proximal constant (C2-type) Ig domain in their extracellular region which are implicated in homotypic adhesion. They are highly expressed during embryonic development in a variety of tissues including the nervous system whereby in adult stages the protein level of CAR and CLMP decreases, only BT-IgSF expression increases within age. CAR-related proteins are concentrated at specialized cell-cell communication sites such as gap or tight junctions and are present at the plasma membrane in larger protein complexes. Considerable progress has been made on the molecular structure and interactions of CAR while research on CLMP and BT-IgSF is at an early stage. Studies on mouse mutants revealed biological functions of CAR in the heart and for CLMP in the gastrointestinal and urogenital systems. Furthermore, CAR and BT-IgSF appear to regulate synaptic function in the hippocampus
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
Highest Weight Modules and Invariant Integrable n-State Models with Periodic Boundary Conditions"
The weights are computed for the Bethe vectors of an RSOS type model with
periodic boundary conditions obeying ()
invariance. They are shown to be highest weight vectors. The q-dimensions of
the corresponding irreducible representations are obtained.Comment: 5 pages, LaTeX, SFB 288 preprin
The kaon semileptonic form factor in Nf=2+1 domain wall lattice QCD with physical light quark masses
We present the first calculation of the kaon semileptonic form factor with
sea and valence quark masses tuned to their physical values in the continuum
limit of 2+1 flavour domain wall lattice QCD. We analyse a comprehensive set of
simulations at the phenomenologically convenient point of zero momentum
transfer in large physical volumes and for two different values of the lattice
spacing. Our prediction for the form factor is f+(0)=0.9685(34)(14) where the
first error is statistical and the second error systematic. This result can be
combined with experimental measurements of K->pi decays for a determination of
the CKM-matrix element for which we predict |Vus|=0.2233(5)(9) where the first
error is from experiment and the second error from the lattice computation.Comment: 21 pages, 7 figures, 6 table
Energy and entropy of relativistic diffusing particles
We discuss energy-momentum tensor and the second law of thermodynamics for a
system of relativistic diffusing particles. We calculate the energy and entropy
flow in this system. We obtain an exact time dependence of energy, entropy and
free energy of a beam of photons in a reservoir of a fixed temperature.Comment: 14 pages,some formulas correcte
First exploratory calculation of the long-distance contributions to the rare kaon decays <i>K</i> →π ℓ<sup>+</sup>ℓ<sup>-</sup>
The rare decays of a kaon into a pion and a charged lepton/antilepton pair
proceed via a flavour changing neutral current and therefore may only be
induced beyond tree level in the Standard Model. This natural suppression makes
these decays sensitive to the effects of potential New Physics. The CP
conserving decay channels however are dominated by a
single photon exchange; this involves a sizeable long-distance hadronic
contribution which represents the current major source of theoretical
uncertainty. Here we outline our methodology for the computation of the
long-distance contributions to these rare decay amplitudes using lattice QCD
and present the numerical results of the first exploratory studies of these
decays in which all but the disconnected diagrams are evaluated. The domain
wall fermion ensembles of the RBC and UKQCD collaborations are used, with a
pion mass of and a kaon mass of . In particular we determine the form factor, , of the
decay from the lattice at small values of
, obtaining for the
three values of respectively.Comment: 40 pages, 14 figures, 4 table
Exact thermodynamics of an Extended Hubbard Model of single and paired carriers in competition
By exploiting the technique of Sutherland's species, introduced in
\cite{DOMO-RC}, we derive the exact spectrum and partition function of a 1D
extended Hubbard model. The model describes a competition between dynamics of
single carriers and short-radius pairs, as a function of on-site Coulomb
repulsion () and filling (). We provide the temperature dependence of
chemical potential, compressibility, local magnetic moment, and specific heat.
In particular the latter turns out to exhibit two peaks, both related to
`charge' degrees of freedom. Their origin and behavior are analyzed in terms of
kinetic and potential energy, both across the metal-insulator transition point
and in the strong coupling regime.Comment: 14 pages, 15 eps figure
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