16,740 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
Structure of Critical Lines in Quenched Lattice QCD with the Wilson Quark Action
The structure of critical lines of vanishing pion mass for the Wilson quark
action is examined in quenched lattice QCD. The numerical evidence is presented
that critical lines spread into five branches beyond beta=5.6-5.7 at zero
temperature. It is also shown that critical lines disappear in the deconfined
phase for the case of finite temperatures.Comment: 11 pages, Latex, 7 Postscript figures, uses epsf.st
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
Operator product expansion and the short distance behavior of 3-flavor baryon potentials
The short distance behavior of baryon-baryon potentials defined through
Nambu-Bethe-Salpeter wave functions is investigated using the operator product
expansion. In a previous analysis of the nucleon-nucleon case, corresponding to
the SU(3) channels and , we argued that the potentials
have a repulsive core. A new feature occurs for the case of baryons made up of
three flavors: manifestly asymptotically attractive potentials appear in the
singlet and octet channels. Attraction in the singlet channel was first
indicated by quark model considerations, and recently been found in numerical
lattice simulations. The latter have however not yet revealed asymptotic
attraction in the octet channels; we give a speculative explanation for this
apparent discrepancy.Comment: 11 pages, 2 figure
Nuclear Force from Monte Carlo Simulations of Lattice Quantum Chromodynamics
The nuclear force acting between protons and neutrons is studied in the Monte
Carlo simulations of the fundamental theory of the strong interaction, the
quantum chromodynamics defined on the hypercubic space-time lattice. After a
brief summary of the empirical nucleon-nucleon (NN) potentials which can fit
the NN scattering experiments in high precision, we outline the basic
formulation to derive the potential between the extended objects such as the
nucleons composed of quarks. The equal-time Bethe-Salpeter amplitude is a key
ingredient for defining the NN potential on the lattice. We show the results of
the numerical simulations on a lattice with the lattice spacing fm (lattice volume (4.4 fm)) in the quenched approximation.
The calculation was carried out using the massively parallel computer Blue
Gene/L at KEK. We found that the calculated NN potential at low energy has
basic features expected from the empirical NN potentials; attraction at long
and medium distances and the repulsive core at short distance. Various future
directions along this line of research are also summarized.Comment: 13 pages, 4 figures, version accepted for publication in
"Computational Science & Discovery" (IOP
Non-Perturbative Determination of in Three-flavor Dynamical QCD
We present a fully non-perturbative determination of the improvement
coefficient in three-flavor dynamical QCD for the RG improved as
well as the plaquette gauge actions, using the Schr\"odinger functional scheme.
Results are compared with one-loop estimates at weak gauge coupling.Comment: 3 pages, 6 figures, Lattice2002(Improvement and Renormalization),
Unnecessary files are remove
Chemical Abundances of the Milky Way Thick Disk and Stellar Halo I.: Implications of [alpha/Fe] for Star Formation Histories in Their Progenitors
We present the abundance analysis of 97 nearby metal-poor (-3.3<[Fe/H]<-0.5)
stars having kinematics characteristics of the Milky Way (MW) thick disk,
inner, and outer stellar halos. The high-resolution, high-signal-to-noise
optical spectra for the sample stars have been obtained with the High
Dispersion Spectrograph mounted on the Subaru Telescope. Abundances of Fe, Mg,
Si, Ca and Ti have been derived using a one-dimensional LTE abundance analysis
code with Kurucz NEWODF model atmospheres. By assigning membership of the
sample stars to the thick disk, inner or outer halo components based on their
orbital parameters, we examine abundance ratios as a function of [Fe/H] and
kinematics for the three subsamples in wide metallicity and orbital parameter
ranges.
We show that, in the metallicity range of -1.5<[Fe/H]<= -0.5, the thick disk
stars show constantly high mean [Mg/Fe] and [Si/Fe] ratios with small scatter.
In contrast, the inner, and the outer halo stars show lower mean values of
these abundance ratios with larger scatter. The [Mg/Fe], [Si/Fe] and [Ca/Fe]
for the inner and the outer halo stars also show weak decreasing trends with
[Fe/H] in the range [Fe/H]. These results favor the scenarios that the MW
thick disk formed through rapid chemical enrichment primarily through Type II
supernovae of massive stars, while the stellar halo has formed at least in part
via accretion of progenitor stellar systems having been chemically enriched
with different timescales.Comment: Accepted for publication in Ap
Electroweak baryogenesis from chargino transport in the supersymmetric model
We study the baryon asymmetry of the universe in the supersymmetric standard
model (SSM). At the electroweak phase transition, the fermionic partners of the
charged SU(2) gauge bosons and Higgs bosons are reflected from or transmitted
to the bubble wallof the broken phase. Owing to a physical complex phase in
their mass matrix, these reflections and transmissions have asymmetries between
CP conjugate processes. Equilibrium conditions in the symmetric phaseare then
shifted to favor a non-vanishing value for the baryon number density, which is
realized through electroweak anomaly. We show that the resultant ratio of
baryon number to entropy is consistent with its present observed value within
reasonable ranges of SSM parameters, provided that the CP-violating phase
intrinsic in the SSM is not much suppressed. The compatibility with the
constraints on the parameters from the electric dipole moment of the neutron is
also discussed.Comment: 23 page
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