185 research outputs found
Spin-3/2 pentaquark in the QCD sum rule
We study and pentaquark states with in
the QCD sum rule approach. The QCD sum rule for positive parity states and that
for negative parity are independently derived. The sum rule suggests that there
exist the and the states. These states may be observed as
extremely narrow peaks since they can be much below the -wave threshold and
since the only allowed decay channels are in -wave, whose centrifugal
barriers are so large that the widths are strongly suppressed. The
state may be assigned to the observed and the state
can be a candidate for .Comment: 27 pages, 14 figure
QCD sum rules for quark-gluon three-body components in the B meson
We discuss the QCD sum rule calculation of the heavy-quark effective theory
parameters, and , which correspond to matrix elements
representing quark-gluon three-body components in the -meson wavefunction.
We derive the sum rules for calculating the new higher-order
QCD corrections, i.e., the order radiative corrections to the Wilson
coefficients associated with the dimension-5 quark-gluon mixed condensates, and
the power corrections due to the dimension-6 vacuum condensates. We find that
the new radiative corrections significantly improve the stability of the
corresponding Borel sum rules and lead to the reduction of the values of
. We also discuss the renormalization-group improvement for the
sum rules and present update on the values of .Comment: 28 pages, 20 figures, version to appear in Nuclear Physics
Two-pion bound state in sigma channel at finite temperature
We study how we can understand the change of the spectral function and the
pole location of the correlation function for sigma at finite temperature,
which were previously obtained in the linear sigma model with a resummation
technique called optimized perturbation theory. There are two relevant poles in
the sigma channel. One pole is the original sigma pole which shows up as a
broad peak at zero temperature and becomes lighter as the temperature
increases. The behavior is understood from the decreasing of the sigma
condensate, which is consistent with the Brown-Rho scaling. The other pole
changes from a virtual state to a bound state of pion-pion as the temperature
increases which causes the enhancement at the pion-pion threshold. The behavior
is understood as the emergence of the pion-pion bound state due to the
enhancement of the pion-pion attraction by the induced emission in medium. The
latter pole, not the former, eventually degenerates with pion above the
critical temperature of the chiral transition. This means that the observable
"sigma" changes from the former to the latter pole, which can be interpreted as
the level crossing of "sigma" and pion-pion at finite temperature.Comment: 4 pages, 4 figure
ppK- bound states from Skyrmions
The bound kaon approach to the strangeness in the Skyrme model is applied to
investigating the possibility of deeply bound states. We describe the
system as two-Skyrmion around which a kaon field fluctuates. Each
Skyrmion is rotated in the space of SU(2) collective coordinate. The rotational
motions are quantized to be projected onto the spin-singlet proton-proton
state. We derive the equation of motion for the kaon in the background field of
two Skyrmions at fixed positions. From the numerical solution of the equation
of motion, it is found that the energy of can be considerably small, and
that the distribution of shows molecular nature of the system.
For this deep binding, the Wess-Zumino-Witten term plays an important role. The
total energy of the system is estimated in the Born-Oppenheimer
approximation. The binding energy of the state is MeV.
The mean square radius of the subsystem is
fm.Comment: Oct 2007, 15 pages, 8 figures; added references, corrected typo
Flavour-singlet g_A and the QCD sum rule incorporating instanton effects
We derive a QCD sum rule for the flavour-singlet axial coupling constant
from a two point correlation function of flavour-singlet axial
vector currents in a one-nucleon state. In evaluating the correlation function
by an operator product expansion we take into account the terms up to dimension
6. This correlation function receives an additional two-loop diagram which
comes from an (anti-)instanton. If we do not include it, is
estimated to be 0.8. However, the additional diagram due to instantons
contributes negatively and reduces towards the experimental value.Comment: 15 pages, 2 figure
Quantum Hall States of Gluons in Quark Matter
We have recently shown that dense quark matter possesses a color
ferromagnetic phase in which a stable color magnetic field arises
spontaneously. This ferromagnetic state has been known to be Savvidy vacuum in
the vacuum sector. Although the Savvidy vacuum is unstable, the state is
stabilized in the quark matter. The stabilization is achieved by the formation
of quantum Hall states of gluons, that is, by the condensation of the gluon's
color charges transmitted from the quark matter. The phase is realized between
the hadronic phase and the color superconducting phase. After a review of
quantum Hall states of electrons in semiconductors, we discuss the properties
of quantum Hall states of gluons in quark matter in detail. Especially, we
evaluate the energy of the states as a function of the coupling constant. We
also analyze solutions of vortex excitations in the states and evaluate their
energies. We find that the states become unstable as the gauge coupling
constant becomes large, or the chemical potential of the quarks becomes small,
as expected. On the other hand, with the increase of the chemical potential,
the color superconducting state arises instead of the ferromagnetic state. We
also show that the quark matter produced by heavy ion collisions generates
observable strong magnetic field Gauss when it enters the
ferromagnetic phase.Comment: 11 pages, 2 figure
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