11,794 research outputs found
Time-Dependent Variational Approach to the Non-Abelian Pure Gauge Theory
The time-dependent variational approach to the pure Yang-Mills gauge theory,
especially a color su(3) gauge theory, is formulated in the functional
Schroedinger picture with a Gaussian wave functional approximation. The
equations of motion for the quantum gauge fields are formulated in the
Liouville-von Neumann form. This variational approach is applied in order to
derive the transport coefficients, such as the shear viscosity, for the pure
gluonic matter by using the linear response theory. As a result, the
contribution to the shear viscosity from the quantum gluons is zero up to the
lowest order of the coupling g in the quantum gluonic matter.Comment: 19 pages, no figures, using PTPTeX.cl
Survival of charmonia above Tc in anisotropic lattice QCD
We find a strong evidence for the survival of and as
spatially-localized (quasi-)bound states above the QCD critical
temperature , by investigating the boundary-condition dependence of their
energies and spectral functions. In a finite-volume box, there arises a
boundary-condition dependence for spatially spread states, while no such
dependence appears for spatially compact states. In lattice QCD, we find almost
{\it no} spatial boundary-condition dependence for the energy of the
system in and channels for . We also
investigate the spectral function of charmonia above in lattice QCD using
the maximum entropy method (MEM) in terms of the boundary-condition dependence.
There is {\it no} spatial boundary-condition dependence for the low-lying peaks
corresponding to and around 3GeV at . These facts
indicate the survival of and as compact
(quasi-)bound states for .Comment: 4 pages, 1 figur
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
Tetraquark and Pentaquark Systems in Lattice QCD
Motivated by the recent experimental discoveries of multi-quark candidates,
e.g., the , we study multi-quark systems in lattice QCD. First,
we perform accurate mass measurements of low-lying 5Q states with and
I=0 in both positive- and negative-parity channels in anisotropic lattice QCD.
The lowest positive-parity 5Q state is found to have a large mass of about
2.24GeV after the chiral extrapolation. To single out the compact 5Q state from
scattering states, we develop a new method with the hybrid-boundary
condition (HBC), and find no evidence of the compact 5Q state below 1.75GeV in
the negative-parity channel. Second, we perform the first study of the
multi-quark potential in lattice QCD to clarify the inter-quark interaction in
multi-quark systems. The 5Q potential for the QQ--QQ system is found to be well described by the ``OGE Coulomb plus
multi-Y Ansatz": the sum of the one-gluon-exchange (OGE) Coulomb term and the
multi-Y-type linear term based on the flux-tube picture. The 4Q potential
for the QQ- system is also described by the
OGE Coulomb plus multi-Y Ansatz, when QQ and are well
separated. The 4Q system is described as a "two-meson" state with disconnected
flux tubes, when the nearest quark and antiquark pair is spatially close. We
observe a lattice-QCD evidence for the ``flip-flop'', i.e., the flux-tube
recombination between the connected 4Q state and the ``two-meson'' state. On
the confinement mechanism, the lattice QCD results indicate the flux-tube-type
linear confinement in multi-quark hadrons.Comment: 22 pages, 3 tables, 16 figures. Talk given at International Workshop
on Quark Nuclear Physics 2005 (QNP05), Phoenix Park, Korea, 22-24, Feb., 200
Nuclear Force from Lattice QCD
The first lattice QCD result on the nuclear force (the NN potential) is
presented in the quenched level. The standard Wilson gauge action and the
standard Wilson quark action are employed on the lattice of the size 16^3\times
24 with the gauge coupling beta=5.7 and the hopping parameter kappa=0.1665. To
obtain the NN potential, we adopt a method recently proposed by CP-PACS
collaboration to study the pi pi scattering phase shift. It turns out that this
method provides the NN potentials which are faithful to those obtained in the
analysis of NN scattering data. By identifying the equal-time Bethe-Salpeter
wave function with the Schroedinger wave function for the two nucleon system,
the NN potential is reconstructed so that the wave function satisfies the
time-independent Schroedinger equation. In this report, we restrict ourselves
to the J^P=0^+ and I=1 channel, which enables us to pick up unambiguously the
``central'' NN potential V_{central}(r). The resulting potential is seen to
posses a clear repulsive core of about 500 MeV at short distance (r < 0.5 fm).
Although the attraction in the intermediate and long distance regions is still
missing in the present lattice set-up, our method is appeared to be quite
promising in reconstructing the NN potential with lattice QCD.Comment: A talk given at the XXIV International Symposium on Lattice Field
Theory (Lattice2006), Tucson, Arizona, USA, July 23-28, 2006, 3 figures,
7page
Anisotropic Lattice QCD Studies of Penta-quark Anti-decuplet
Anti-decuplet penta-quark baryon is studied with the quenched anisotropic
lattice QCD for accurate measurement of the correlator. Both the positive and
negative parity states are studied using a non-NK type interpolating field with
I=0 and J=1/2. After the chiral extrapolation, the lowest positive parity state
is found at m_{Theta} \simeq 2.25 GeV, which is too massive to be identified
with the experimentally observed Theta^+(1540). The lowest negative parity
state is found at m_{Theta}\simeq 1.75 GeV, which is rather close to the
empirical value. To confirm that this state is a compact 5Q resonance, a new
method with ``hybrid boundary condition (HBC)'' is proposed. The HBC analysis
shows that the observed state in the negative parity channel is an NK
scattering state.Comment: A talk given at International Workshop PENTAQUARK04, July 20-23, 2004
at SPring-8, Japan, 8 pages, 7 figures, 2 table
Flat-band excitonic states in Kagome lattice on semiconductor surface
Excitonic properties in the Kagome lattice system, which is produced by
quantum wires on semiconductor surfaces, are investigated by using the exact
diagonalization of a tight binding model. It is shown that due to the existence
of flat bands the binding energy of exciton becomes remarkably large in the
two-dimensional Kagome lattice compared to that in one-dimensional lattice, and
the exciton Bohr radius is quite small as large as a lattice constant. We also
discuss the magnetic field effects on the exciton binding energy and the
stability of exciton against the creation of charged exciton and biexciton.Comment: 5 pages, 5 figure
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