456 research outputs found
Application of DWF to heavy-light mesons
We consider application of domain wall fermions to quarks with relatively
heavy masses, aiming at precision calculations of charmed meson properties.
Preliminary results for a few basic quantities are presented.Comment: Lattice2003(heavy), 3 pages, 3 figure
Financial Time Series Analysis of SV Model by Hybrid Monte Carlo
We apply the hybrid Monte Carlo (HMC) algorithm to the financial time sires
analysis of the stochastic volatility (SV) model for the first time. The HMC
algorithm is used for the Markov chain Monte Carlo (MCMC) update of volatility
variables of the SV model in the Bayesian inference. We compute parameters of
the SV model from the artificial financial data and compare the results from
the HMC algorithm with those from the Metropolis algorithm. We find that the
HMC decorrelates the volatility variables faster than the Metropolis algorithm.
We also make an empirical analysis based on the Yen/Dollar exchange rates.Comment: 8 pages, 3 figures, to be published in LNC
Current status of Dynamical Overlap project
We discuss the adaptation of the Hybrid Monte Carlo algorithm to overlap
fermions. We derive a method which can be used to account for the delta
function in the fermionic force caused by the differential of the sign
function. We discuss the algoritmic difficulties that have been overcome, and
mention those that still need to be solved.Comment: Talk given at Workshop on Computational Hadron Physics, Nicosia,
September 2005. 8 page
The phase structure of lattice QCD with two flavours of Wilson quarks and renormalization group improved gluons
The effect of changing the lattice action for the gluon field on the recently
observed [1] first order phase transition near zero quark mass is investigated
by replacing the Wilson plaquette action by the DBW2 action. The lattice action
for quarks is unchanged: it is in both cases the original Wilson action. It
turns out that Wilson fermions with the DBW2 gauge action have a phase
structure where the minimal pion mass and the jump of the average plaquette are
decreased, when compared to Wilson fermions with Wilson plaquette action at
similar values of the lattice spacing. Taking the DBW2 gauge action is
advantageous also from the point of view of the computational costs of
numerical simulations.Comment: 34 pages, 3 tables, 14 figures; revised version to appear in EPJ
The Kentucky Noisy Monte Carlo Algorithm for Wilson Dynamical Fermions
We develop an implementation for a recently proposed Noisy Monte Carlo
approach to the simulation of lattice QCD with dynamical fermions by
incorporating the full fermion determinant directly. Our algorithm uses a
quenched gauge field update with a shifted gauge coupling to minimize
fluctuations in the trace log of the Wilson Dirac matrix. The details of tuning
the gauge coupling shift as well as results for the distribution of noisy
estimators in our implementation are given. We present data for some basic
observables from the noisy method, as well as acceptance rate information and
discuss potential autocorrelation and sign violation effects. Both the results
and the efficiency of the algorithm are compared against those of Hybrid Monte
Carlo.
PACS Numbers: 12.38.Gc, 11.15.Ha, 02.70.Uu Keywords: Noisy Monte Carlo,
Lattice QCD, Determinant, Finite Density, QCDSPComment: 30 pages, 6 figure
GRIP1 enhances estrogen receptor α-dependent extracellular matrix gene expression in chondrogenic cells
SummaryObjectiveThe role of postmenopause on the pathogenesis of cartilage degeneration has been an open question. We assessed cartilage degeneration in estrogen receptor (ER)α null mice and examined the role of glucocorticoid receptor-interacting protein 1 (GRIP1) in the ERα-dependent transcription of a type II collagen gene (col2a1) with special reference to a crosstalk with the transforming growth factor (TGF)-β signaling pathway.MethodsThe vertebral cartilaginous endplate from female ERα null mice was subjected to histological analyses. Col2a1 expression of primary chondrocytes (PCs) obtained from ERα null mice after 17β-estradiol (E2) and TGF-β1 stimulation was examined by reverse transcription polymerase chain reaction (RT-PCR). Estrogen response element (ERE) or col2a1 promoter–enhancer luciferase reporter system was used to investigate the crosstalk among ERα, GRIP1, and MKK6. Col2a1 expression and glycosaminoglycan (GAG) content were measured in ATDC5 cells treated with GRIP1 small interfering RNA (siRNA).ResultsERα deficiency clearly accelerated impairment of the vertebral cartilaginous endplate. E2 and TGF-β1 stimulation increased col2a1 expression in PC from wild-type mice, but not that from ERα null mice. The same stimulation increased the col2a1 promoter–enhancer reporter activity, and the elevated activity was decreased by dominant-negative ERα and p38 mitogen-activated protein kinase (MAPK) inhibitor. GRIP1 increased the E2-dependent ERE activation in the presence of ERα and constitutive-active MKK6. GRIP1 siRNA repressed col2a1 expression and GAG production in ATDC5 cells.ConclusionsCrosstalks between ERα/GRIP1 and TGF-β/MKK6/p38 MAPK pathway have protective roles on cartilage metabolism via regulating the extracellular matrices expression. The finding may lead to the development of a novel therapeutic approach for cartilage degeneration
The Deconfinement Phase Transition in One-Flavour QCD
We present a study of the deconfinement phase transition of one-flavour QCD,
using the multiboson algorithm. The mass of the Wilson fermions relevant for
this study is moderately large and the non-hermitian multiboson method is a
superior simulation algorithm. Finite size scaling is studied on lattices of
size , and . The behaviours of the
peak of the Polyakov loop susceptibility, the deconfinement ratio and the
distribution of the norm of the Polyakov loop are all characteristic of a
first-order phase transition for heavy quarks. As the quark mass decreases, the
first-order transition gets weaker and turns into a crossover. To investigate
finite size scaling on larger spatial lattices we use an effective action in
the same universality class as QCD. This effective action is constructed by
replacing the fermionic determinant with the Polyakov loop identified as the
most relevant Z(3) symmetry breaking term. Higher-order effects are
incorporated in an effective Z(3)-breaking field, , which couples to the
Polyakov loop. Finite size scaling determines the value of where the first
order transition ends. Our analysis at the end - point, , indicates
that the effective model and thus QCD is consistent with the universality class
of the three dimensional Ising model.
Matching the field strength at the end point, , to the
values used in the dynamical quark simulations we estimate the end point,
, of the first-order phase transition. We find which corresponds to a quark mass of about 1.4 GeV .Comment: LaTex, 25 pages, 18 figure
Scaling Study of Pure Gauge Lattice QCD by Monte Carlo Renormalization Group Method
The scaling behavior of pure gauge SU(3) in the region is
examined by a Monte Carlo Renormalization Group analysis. The coupling shifts
induced by factor 2 blocking are measured both on 32 and 16 lattices
with high statistics. A systematic deviation from naive 2-loop scaling is
clearly seen. The mean field and effective coupling constant schemes explain
part, but not all of the deviation. It can be accounted for by a suitable
change of coupling constant, including a correction term in the
2-loop lattice -function. Based on this improvement,
is estimated to be from the analysis of the string tension .Comment: 4 pages of A4 format including 7-postscript figure
Numerical Methods for the QCD Overlap Operator IV: Hybrid Monte Carlo
The extreme computational costs of calculating the sign of the Wilson matrix
within the overlap operator have so far prevented four dimensional dynamical
overlap simulations on realistic lattice sizes, because the computational power
required to invert the overlap operator, the time consuming part of the Hybrid
Monte Carlo algorithm, is too high. In this series of papers we introduced the
optimal approximation of the sign function and have been developing
preconditioning and relaxation techniques which reduce the time needed for the
inversion of the overlap operator by over a factor of four, bringing the
simulation of dynamical overlap fermions on medium-size lattices within the
range of Teraflop-computers.
In this paper we adapt the HMC algorithm to overlap fermions. We approximate
the matrix sign function using the Zolotarev rational approximation, treating
the smallest eigenvalues of the Wilson operator exactly within the fermionic
force. We then derive the fermionic force for the overlap operator, elaborating
on the problem of Dirac delta-function terms from zero crossings of eigenvalues
of the Wilson operator. The crossing scheme proposed shows energy violations
which are better than O() and thus are comparable with the
violations of the standard leapfrog algorithm over the course of a trajectory.
We explicitly prove that our algorithm satisfies reversibility and area
conservation. Finally, we test our algorithm on small , , and
lattices at large masses.Comment: v2 60 pages; substantial changes to all parts of the article; v3
minor revsion
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