18,746 research outputs found
Baryon-Baryon Interactions from Lattice QCD
We report on new attempt to investigate baryon-baryon interactions in lattice
QCD. From the Bethe-Salpeter (BS) wave function, we have successfully extracted
the nucleon-nucleon () potentials in quenched QCD simulations, which
reproduce qualitative features of modern potentials. The method has been
extended to obtain the tensor potential as well as the central potential and
also applied to the hyperon-nucleon () interactions, in both quenched and
full QCD.Comment: 6 pages, 10 figures, A plenary talk given at the 5-th International
Conference on Quark and Nuclear Physics, Beijing, September 21-26, 200
Spontaneous Flavor and Parity Breaking with Wilson Fermions
We discuss the phase diagram of Wilson fermions in the -- plane for
two-flavor QCD. We argue that, as originally suggested by Aoki, there is a
phase in which flavor and parity are spontaneously broken. Recent numerical
results on the spectrum of the overlap Hamiltonian have been interpreted as
evidence against Aoki's conjecture. We show that they are in fact consistent
with the presence of a flavor-parity broken ``Aoki phase''. We also show how,
as the continuum limit is approached, one can study the lattice theory using
the continuum chiral Lagrangian supplemented by additional terms proportional
to powers of the lattice spacing. We find that there are two possible phase
structures at non-zero lattice spacing: (1) there is an Aoki phase of width
with two massless Goldstone pions; (2) there is no
symmetry breaking, and all three pions have an equal non-vanishing mass of
order . Present numerical evidence suggests that the former option is
realized for Wilson fermions. Our analysis then predicts the form of the pion
masses and the flavor-parity breaking condensate within the Aoki phase. Our
analysis also applies for non-perturbatively improved Wilson fermions.Comment: 22 pages, LaTeX, 5 figures (added several references and a comment
Lattice QCD and Hydro/Cascade Model of Heavy Ion Collisions
We report here on a recent lattice study of the QCD transition region at
finite temperature and zero chemical potential using domain wall fermions
(DWF). We also present a parameterization of the QCD equation of state obtained
from lattice QCD that is suitable for use in hydrodynamics studies of heavy ion
collisions. Finally, we show preliminary results from a multi-stage
hydrodynamics/hadron cascade model of a heavy ion collision, in an attempt to
understand how well the experimental data (e.g. particle spectra, elliptic
flow, and HBT radii) can constrain the inputs (e.g. initial temperature,
freezeout temperature, shear viscosity, equation of state) of the theoretical
model.Comment: 10 pages, 12 figures. Proceedings for the 26th Winter Workshop on
Nuclear Dynamics, Ocho Rios, Jamaica, Jan 2-9, 201
Domain Wall Fermions in Quenched Lattice QCD
We study the chiral properties and the validity of perturbation theory for
domain wall fermions in quenched lattice QCD at beta=6.0. The explicit chiral
symmetry breaking term in the axial Ward-Takahashi identity is found to be very
small already at Ns=10, where Ns is the size of the fifth dimension, and its
behavior seems consistent with an exponential decay in Ns within the limited
range of Ns we explore. From the fact that the critical quark mass, at which
the pion mass vanishes as in the case of the ordinary Wilson-type fermion,
exists at finite Ns, we point out that this may be a signal of the parity
broken phase and investigate the possible existence of such a phase in this
model at finite Ns. The rho and pi meson decay constants obtained from the
four-dimensional local currents with the one-loop renormalization factor show a
good agreement with those obtained from the conserved currents
Nucleon-nucleon interactions via Lattice QCD: Methodology --HAL QCD approach to extract hadronic interactions in lattice QCD--
We review the potential method in lattice QCD, which has recently been
proposed to extract nucleon-nucleon interactions via numerical simulations. We
focus on the methodology of this approach by emphasizing the strategy of the
potential method, the theoretical foundation behind it, and special numerical
techniques. We compare the potential method with the standard finite volume
method in lattice QCD, in order to make pros and cons of the approach clear. We
also present several numerical results for the nucleon-nucleon potentials.Comment: 12 pages, 10 figure
Observations on discretization errors in twisted-mass lattice QCD
I make a number of observations concerning discretization errors in
twisted-mass lattice QCD that can be deduced by applying chiral perturbation
theory including lattice artifacts. (1) The line along which the PCAC quark
mass vanishes in the twisted mass-twisted mass plane makes an angle to the
untwisted mass axis which is a direct measure of O(a) terms in the chiral
Lagrangian, and is found numerically to be large; (2) Numerical results for
pionic quantities in the mass plane show the qualitative properties predicted
by chiral perturbation theory, in particular an asymmetry in slopes between
positive and negative untwisted quark masses; (3) By extending the description
of the ``Aoki regime'' (where m_q is of size a^2 Lambda_QCD^3) to
next-to-leading order in chiral perturbation theory I show how the phase
transition lines and lines of maximal twist (using different definitions)
extend into this region, and give predictions for the functional form of pionic
quantities; (4) I argue that the recent claim that lattice artifacts at maximal
twist have apparent infrared singularities in the chiral limit results from
expanding about the incorrect vacuum state. Shifting to the correct vacuum (as
can be done using chiral perturbation theory) the apparent singularities are
summed into non-singular, and furthermore predicted, forms. I further argue
that there is no breakdown in the Symanzik expansion in powers of lattice
spacing, and no barrier to simulating at maximal twist in the Aoki regime.Comment: 20 pages, 6 figures. Published version. More typos corrected, and
summary paragraph added to sections II and I
Composite components under impact load and effects of defects on the loading capacity
Investigations were carried out on a horizontal tail assembly made of carbon fiber reinforced plastic for the Alpha Jet. The possibility of obtaining a leading edge nose design lighter but not more expensive than a metal version was studied. An important consideration was sufficient resistance of the leading edge against impact of stones and hailstones combined with high degree of stiffness. The improvement of energy reception characteristics of the materials through suitable laminate design was considered. Since certain defects occur in structural components, the effects of such defects on the characteristics of the parts were also studied
The Weakly Coupled Gross-Neveu Model with Wilson Fermions
The nature of the phase transition in the lattice Gross-Neveu model with
Wilson fermions is investigated using a new analytical technique. This involves
a new type of weak coupling expansion which focuses on the partition function
zeroes of the model. Its application to the single flavour Gross-Neveu model
yields a phase diagram whose structure is consistent with that predicted from a
saddle point approach. The existence of an Aoki phase is confirmed and its
width in the weakly coupled region is determined. Parity, rather than chiral
symmetry breaking naturally emerges as the driving mechanism for the phase
transition.Comment: 15 pages including 1 figur
Improving Dynamical Domain-Wall Fermion Simulations
We report on studies of the chiral properties of dynamical domain wall
fermions combined with the DBW2 gauge action for different gauge couplings and
fermion masses. For quenched theories, the DBW2 action gives a residual chiral
symmetry breaking much smaller than what was found with more traditional
choices for the gauge action. Our goal is to investigate the possibilities
which this and further improvements provide for the study of QCD thermodynamics
and other simulations at stronger couplings.Comment: 3 pages, 4 figures, 3 tables, Lattice2003(improve
Nonet Singlet-Octet Mixing Angle, Strange Quark Mass, and Strange Quark Condensate
Two strategies are taken into account to determine the
- mixing angle . (i) First, using the
Gell-Mann-Okubo mass formula together with the - mixing
angle extracted from the data for , and , gave . (ii) Second, from the study of the ratio for
and branching
fractions, we have two-fold solution or
. Combining these two analyses, we thus obtain
. We further compute the strange quark mass
and strange quark condensate from the analysis of the
mass difference QCD sum rule, where the operator-product-expansion series is up
to dimension six and to accuracy.
Using the average of the recent lattice results and the value that we
have obtained as inputs, we get .Comment: 10 pages, 1 table, published versio
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