9,214 research outputs found
Chiral Phase Transition in Lattice QCD with Wilson Quarks
The nature of the chiral phase transition in lattice QCD is studied for the
cases of 2, 3 and 6 flavors with degenerate Wilson quarks, mainly on a lattice
with the temporal direction extension . We find that the chiral phase
transition is continuous for the case of 2 flavors, while it is of first order
for 3 and 6 flavors.Comment: uuencoded compressed tar file, LaTeX, 14 pages, 7 figure
Phase structure of lattice QCD for general number of flavors
We investigate the phase structure of lattice QCD for the general number of
flavors in the parameter space of gauge coupling constant and quark mass,
employing the one-plaquette gauge action and the standard Wilson quark action.
Performing a series of simulations for the number of flavors --360 with
degenerate-mass quarks, we find that when there is a line of a bulk
first order phase transition between the confined phase and a deconfined phase
at a finite current quark mass in the strong coupling region and the
intermediate coupling region. The massless quark line exists only in the
deconfined phase. Based on these numerical results in the strong coupling limit
and in the intermediate coupling region, we propose the following phase
structure, depending on the number of flavors whose masses are less than
which is the physical scale characterizing the phase transition in
the weak coupling region: When , there is only a trivial IR fixed
point and therefore the theory in the continuum limit is free. On the other
hand, when , there is a non-trivial IR fixed point and
therefore the theory is non-trivial with anomalous dimensions, however, without
quark confinement. Theories which satisfy both quark confinement and
spontaneous chiral symmetry breaking in the continuum limit exist only for .Comment: RevTeX, 20 pages, 43 PS figure
Time dependent CP asymmetry in decay to probe the origin of CP violation
Since the CP violation in the system has been investigated up to now only
through processes related to the -- mixing, urgently required is
new way of study for the CP violation and establishing its origin in the
system independent of the mixing process. In this work, we explore the
exclusive decay to obtain the time-dependent CP
asymmetry in decay process in the standard model and the
supersymmetric model. We find that the complex RL and RR mass insertion to the
squark sector in the MSSM can lead to a large CP asymmetry in
decay through the gluino-squark diagrams, which is not predicted in the
Standard Model induced by the -- mixing.Comment: 10 pages, 4 eps figure
Finite Temperature Transitions in Lattice QCD with Wilson Quarks --- Chiral Transitions and the Influence of the Strange Quark ---
The nature of finite temperature transitions in lattice QCD with Wilson
quarks is studied near the chiral limit for the cases of 2, 3, and 6 flavors of
degenerate quarks (, 3, and 6) and also for the case of massless up and
down quarks and a light strange quark (). Our simulations mainly
performed on lattices with the temporal direction extension indicate
that the finite temperature transition in the chiral limit (chiral transition)
is continuous for , while it is of first order for and 6. We
find that the transition is of first order for the case of massless up and down
quarks and the physical strange quark where we obtain a value of
consistent with the physical value. We also discuss the phase
structure at zero temperature as well as that at finite temperatures.Comment: uuencoded compressed tar file, 70 pages, 32 figure
SU(3) lattice gauge theory with a mixed fundamental and adjoint plaquette action: Lattice artefacts
We study the four-dimensional SU(3) gauge model with a fundamental and an
adjoint plaquette term in the action. We investigate whether corrections to
scaling can be reduced by using a negative value of the adjoint coupling. To
this end, we have studied the finite temperature phase transition, the static
potential and the mass of the 0^{++} glueball. In order to compute these
quantities we have implemented variance reduced estimators that have been
proposed recently. Corrections to scaling are analysed in dimensionless
combinations such as T_c/\sqrt{\sigma} and m_{0^{++}}/T_c. We find that indeed
the lattice artefacts in e.g. m_{0^{++}}/T_c can be reduced considerably
compared with the pure Wilson (fundamental) gauge action at the same lattice
spacing.Comment: 36 pages, 12 figure
Spatial structure of quark Cooper pairs in a color superconductor
Spatial structure of Cooper pairs with quantum numbers color 3^*, I=J=L=S=0
in ud 2 flavor quark matter is studied by solving the gap equation and
calculating the coherence length in full momentum range without the weak
coupling approximation. Although the gap at the Fermi surface and the coherence
length depend on density weakly, the shape of the r-space pair wave function
varies strongly with density. This result indicates that quark Cooper pairs
become more bosonic at higher densities.Comment: 10 pages, 3 figures. The frequency dependence of the gap and the
limitation on the type I/type II discussion are mentioned briefly. To appear
in Phys. Rev.
QCD thermodynamics with two flavors of Wilson quarks at N_t=6
We report on a study of hadron thermodynamics with two flavors of Wilson
quarks on 12^3x6 lattices. We have studied the crossover between the high and
low temperature regimes for three values of the hopping parameter, kappa=0.16,
0.17, and 0.18. At each of these values of kappa we have carried out spectrum
calculations on 12^3x24 lattices for two values of the gauge coupling in the
vicinity of the crossover in order to set an energy scale for our
thermodynamics calculations and to determine the critical value of the gauge
coupling for which the pion and quark masses vanish. For kappa=0.17 and 0.18 we
find coexistence between the high and low temperature regimes over 1,000
simulation time units indicating either that the equilibration time is
extremely long or that there is a possibility of a first order phase
transition. The pion mass is large at the crossover values of the gauge
coupling, but the crossover curve has moved closer to the critical curve along
which the pion and quark masses vanish, than it was on lattices with four time
slices. In addition, values of the dimensionless quantity T_c/m_rho are in
closer agreement with those for staggered quarks than was the case at N_t=4. (A
POSTSCRIPT VERSION OF THIS PAPER IS AVAILABLE BY ANONYMOUS FTP FROM
sarek.physics.ucsb.edu (128.111.8.250) IN THE FILE pub/wilson_thermo.ps)Comment: 24 page
Testing improved actions for dynamical Kogut-Susskind quarks
We extend tests of "Naik" and "fat link" improvements of the Kogut-Susskind
quark action to full QCD simulations, and verify that the improvements
previously demonstrated in the quenched approximation apply also to dynamical
quark simulations. We extend the study of flavor symmetry improvement to the
complete set of pions, and find that the nonlocal pions are significantly
heavier than the local non-Goldstone pion. These results can be used to
estimate the lattice spacing necessary for realistic simulations with this
action.Comment: 16 pages, LaTeX, PostScript figures include
What Thermodynamics tells about QCD Plasma near Phase Transition
Due to a rapid change of the entropy density across the critical
temperature of the QCD phase transition, the pressure and the
energy density above generally deviate from their Stefan-Boltzmann
values. We shall demonstrate this both analytically and numerically for a
general class of consistent with thermodynamical constraints and make a
qualitative comparison of the result with the lattice QCD data. Quantities
related to such as the specific heat and sound velocity are also
discussed.Comment: 6 pages revtex, 4 postscript figure
Large Scale Inhomogeneities from the QCD Phase Transition
We examine the first-order cosmological QCD phase transition for a large
class of parameter values, previously considered unlikely. We find that the
hadron bubbles can nucleate at very large distance scales, they can grow as
detonations as well as deflagrations, and that the phase transition may be
completed without reheating to the critical temperature. For a subset of the
parameter values studied, the inhomogeneities generated at the QCD phase
transition might have a noticeable effect on nucleosynthesis.Comment: 15 LaTeX pages + 6 PostScript figures appended at the end of the
file, HU-TFT-94-1
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