arXiv
(422.153 recursos)
This is one of the most extensive subject based repositories in the world in the field of physics, mathematics, astronomy, computer sciences and quantitative biology. This is the principal site with almost 20 mirror versions around the globe. The site is supported by an extensive collection of information and background documentation. An RSS feed is available for anyone interested in keeping up-to-date with newly added materials.
Mostrando recursos 1 - 20 de 10.831
1.
BK from the lattice with Wilson quarks - Becirevic, D.; Boucaud, Ph.; Gimenez, V.; Lubicz, V.; Papinutto, M.
We report our results for the bag-parameter BK obtained from the quenched
simulations on the lattice with Wilson fermions at three values of the lattice
spacing. We implemented the method by which no subtraction of the mixing with
other four-fermion dS=2 operators is needed. Our final result, in terms of the
renormalisation group invariant bag-parameter, is BK = 0.96 +/- 0.10.
2.
Numerical Stochastic Perturbation Theory for full QCD - Di Renzo, F.; Scorzato, L.
We give a full account of the Numerical Stochastic Perturbation Theory method
for Lattice Gauge Theories. Particular relevance is given to the inclusion of
dynamical fermions, which turns out to be surprisingly cheap in this context.
We analyse the underlying stochastic process and discuss the convergence
properties. We perform some benchmark calculations and - as a byproduct - we
present original results for Wilson loops and the 3-loop critical mass for
Wilson fermions.
3.
Neutron Electric Dipole Moment with Domain Wall Quarks - Berruto, F.; Blum, T.; Orginos, K.; Soni, A.
We present preliminary results for nucleon dipole moments computed with
domain wall fermions. Our main target is the electric dipole moment of the
neutron arising from the theta term in the gauge part of the QCD lagrangian.
The calculated magnetic dipole moments of the proton and neutron are in rough
accord with experimental values.
4.
Dirac zero-modes in compact U(1) gauge theory - Drescher, Thomas; Lang, C. B.
We study properties of the zero and near-zero eigenmodes of the overlap Dirac
operator in compact U(1) gauge theory. In the confinement phase the exact
zero-modes are localized as found by studying the values of the inverse
participation ratio and other features. Non-zero-eigenmodes are less localized
in the confinement phase. In the Coulomb phase no zero-modes are observed and
the eigenmodes show no localization at all.
5.
Physics at Tevatron Run II - Zieminska, Daria
We present recent physics results from the Tevatron Collider experiments CDF
and D0. (contribution to Lattice 2004)
6.
Searching for chiral logs in the static-light decay constant - McNeile, UKQCD Collaboration:C; Michael, C.
Using the clover fermion action in unquenched QCD with pion masses as low as
420 MeV, we look for evidence for chiral logs in the static-light decay
constant. There is some evidence for a chiral log term, if the original static
theory of Eichten and Hill is used. However, the more precise data from the
static action of the ALPHA collaboration do not show any evidence for
non-linear dependence of the static-light decay constant on the light quark
mass. We make some comments on the connection between chiral perturbation
theory for decay constants of the pion and static-light meson.
7.
Asymptotic series for distributions - Petrov, Vladimir K.
Asymptotic expansions for a wide class of distribution are studied. A simple
method for computation of the series coefficients is suggested. The case when
regularization parameter of the distribution depends on the asymptotic
parameter is considered.
8.
Twisted Boundary Conditions in Lattice Simulations - Sachrajda, C. T.; Villadoro, G.
By imposing twisted boundary conditions on quark fields it is possible to
access components of momenta other than integer multiples of 2pi/L on a lattice
with spatial volume L^3. We use Chiral Perturbation Theory to study
finite-volume effects with twisted boundary conditions for quantities without
final-state interactions, such as meson masses, decay constants and
semileptonic form factors, and confirm that they remain exponentially small
with the volume. We show that this is also the case for "partially twisted"
boundary conditions, in which (some of) the valence quarks satisfy twisted
boundary conditions but the sea quarks satisfy periodic boundary conditions.
This observation implies that it is not necessary to generate...
9.
Systematics of Staggered Fermion Spectral Properties and Topology - Wong, Kit Yan; Woloshyn, R. M.
The spectral properties of a variety of improved staggered operators are
studied in quenched QCD. The systematic dependence of the infrared eigenvalue
spectrum on i) improvement in the staggered operator, ii) improvement in the
gauge field action, iii) lattice spacing and iv) lattice volume, is analyzed.
It is observed that eigenmodes with small eigenvalues and large chirality
appear as the level of improvement increases or as one approaches the continuum
limit. These eigenmodes can be identified as the ``zero modes'' which
contribute to the chirality associated, via the index theorem, with the
topology of the background gauge field. This gives evidence that staggered
fermions are sensitive to gauge field...
10.
Derivation of Chiral Lagrangians from Random Lattice QCD - Pavlovsky, Oleg V.
In our work we extend the ideas of the derivation of the chiral effective
theory from the lattice QCD [1] to the case of the random lattice
regularization of QCD. Such procedure allows in principle to find contribution
of any order into the chiral effective lagrangian. It is shown that an infinite
subseries of the chiral perturbation can be summed up into tne Born-Infeld term
and the logarithmic correction to them.
11.
Physics issues in simulations with dynamical overlap fermions - DeGrand, Thomas; Schaefer, Stefan
We discuss the impact of various improvements on simulations of dynamical
overlap fermions using the Hybrid Monte Carlo algorithm. We focus on the usage
of fat links and multiple pseudo-fermion fields.
12.
Gauge Singularities in the SU(2) Vacuum on the Lattice - Gutbrod, F.
SU(2) configurations, which have been generated by the Wilson action, are
transformed to a Landau gauge and smoothed by Fourier filtering. This leads to
sharp peaks in the field strengths and in related quantities. These spikes are
caused by gauge singularities. Their density is determined as 1.5 spikes per
fm**4, and it scales with the string tension. The number of spikes vanishes
when approaching the deconfinement regions. Correlations of spikes with Gribov
copies, with cooled action maxima and with the gluon propagator are studied.
13.
Experiences with dynamical chirally improved fermions - Lang, C. B.; Majumdar, Pushan; Ortner, Wolfgang
We simulate Quantum Chromodynamics (QCD) in four Euclidean dimensions with
two (degenerate mass) flavors of dynamical quarks. The Dirac operator we use is
the so-called chirally improved Dirac operator. We discuss the algorithm used
for the simulation as well as the checks and some results on lattices up to
size 8**4 for fermion mass parameters down to 0.1. This is the first attempt to
introduce dynamical quarks with the chirally improved Dirac operator.
14.
On the derivation of effective field theories - Uzunov, Dimo I.
A general self-consistency approach allows a thorough treatment of the
corrections to the standard mean-field approximation (MFA). The natural
extension of standard MFA with the help of a cumulant expansion leads to a new
point of view on the effective field theories. The proposed approach can be
used for a systematic treatment of fluctuation effects of various length scales
and, perhaps, for the development of a new coarse graining procedure. We
outline and justify our method by some preliminary calculations. Concrete
results are given for the critical temperature and the Landau parameters of the
$\phi^4_d$-theory - the field counterpart of the Ising model. An important
unresolved problem of the...
15.
Twisted valence quarks and hadron interactions on the lattice - Bedaque, Paulo F.; Chen, Jiunn-Wei
We consider QCD with valence and sea quarks obeying different boundary
conditions. We point out that the energy of low lying two hadron states do not
depend on the boundary condition of the sea quarks (up to exponentially small
corrections). Thus, the advantages in using twisted boundary conditions on the
lattice QCD extraction of nucleon-nucleon phase shifts can be gained without
the need of new gauge configurations, even in fully unquenched calculations.
16.
Gauge transformations in lattice chiral theories - Kerler, Werner
We show that gauge-transformation properties of correlation functions in
chiral gauge theories on the finite lattice are determined in a general way.
17.
Canonical Approach to Ginsparg-Wilson Fermion - Matsui, Kosuke; Okamoto, Tomohiro; Fujiwara, Takanori
Based upon the lattice Dirac operator satisfying the Ginsparg-Wilson
relation, we investigate canonical formulation of massless fermion on the
spatial lattice. For free fermion system exact chiral symmetry can be
implemented without species doubling. In the presence of gauge couplings the
chiral symmetry is violated. We show that the divergence of the axial vector
current is related to the chiral anomaly in the classical continuum limit.
18.
Efficient Simulation of Heavy Quark Vacuum Polarization - Nobes, Matthew
We outline a simple way to include heavy quark vacuum polarization in lattice
QCD simulations. The method, based on effective field theory, requires only a
trivial modification of the gluon action and has no impact on simulation times.
We assess the range of validity for this procedure, and the impact that it may
have.
19.
Extrapolation of lattice QCD results beyond the power-counting regime - Leinweber, D. B.; Thomas, A. W.; Young, R. D.
Resummation of the chiral expansion is necessary to make accurate contact
with current lattice simulation results of full QCD. Resummation techniques
including relativistic formulations of chiral effective field theory and
finite-range regularization (FRR) techniques are reviewed, with an emphasis on
using lattice simulation results to constrain the parameters of the chiral
expansion. We illustrate how the chiral extrapolation problem has been solved
and use FRR techniques to identify the power-counting regime (PCR) of chiral
perturbation theory. To fourth-order in the expansion at the 1% tolerance
level, we find 0 \le m_pi \le 0.18 GeV for the PCR, extending only a small
distance beyond the physical pion mass.
20.
Finite Volume Dependence of Hadron Properties and Lattice QCD - Thomas, A. W.; Ashley, J. D.; Leinweber, D. B.; Young, R. D.
Because the time needed for a simulation in lattice QCD varies at a rate
exceeding the fourth power of the lattice size, it is important to understand
how small one can make a lattice without altering the physics beyond
recognition. It is common to use a rule of thumb that the pion mass times the
lattice size should be greater than (ideally much greater than) four (i.e.,
$m_\pi L \gg 4$). By considering a relatively simple chiral quark model we are
led to suggest that a more realistic constraint would be $m_\pi (L - 2R) \gg
4$, where $R$ is the radius of the confinement region, which...
1.
