175 research outputs found
Renormalization group dependence of the QCD coupling
The general relation between the standard expansion coefficients and the beta
function for the QCD coupling is exactly derived in a mathematically strict
way. It is accordingly found that an infinite number of logarithmic terms are
lost in the standard expansion with a finite order, and these lost terms can be
given in a closed form. Numerical calculations, by a new matching-invariant
coupling with the corresponding beta function to four-loop level, show that the
new expansion converges much faster.Comment: 6 pages, 2 figures, RevTex4 styl
Chiral condensates and size of the sigma term
The in-medium chiral condensate is studied with a new approach which has the
advantage of no need for extra assumptions on the current mass derivatives of
model parameters. It is shown that the pion-nucleon sigma term is 9/2 times the
average current mass of light quarks, if quark confinement is linear.
Considering both perturbative and non-perturbative interactions, the chiral
condensate decreases monotonously with increasing densities, approaching to
zero at about 4 fm^{-3}.Comment: 11 pages, 1 figure, elsart styl
New solutions for the color-flavor locked strangelets
Recent publications rule out the negatively charged beta equilibrium
strangelets in ordinary phase, and the color-flavor locked (CFL) strangelets
are reported to be also positively charged. This letter presents new solutions
to the system equations where CFL strangelets are slightly negatively charged.
If the ratio of the square-root bag constant to the gap parameter is smaller
than 170 MeV, the CFL strangelets are more stable than iron and the normal
unpaired strangelets. For the same parameters, however, the positively charged
CFL strangelets are more stable.Comment: 5 pages, 4 figures, Revtex4 styl
Mass formulas and thermodynamic treatment in the mass-density-dependent model of strange quark matter
The previous treatments for strange quark matter in the quark
mass-density-dependent model have unreasonable vacuum limits. We provide a
method to obtain the quark mass parametrizations and give a self-consistent
thermodynamic treatment which includes the MIT bag model as an extreme. In this
treatment, strange quark matter in bulk still has the possibility of absolute
stability. However, the lower density behavior of the sound velocity is
opposite to previous findings.Comment: Formatted in REVTeX 3.1, 5 pages, 3 figures, to appear in PRC6
Stability of strangelet at finite temperature
Using the quark mass density- and temperature dependent model, we have
studied the thermodynamical properties and the stability of strangelet at
finite temperature. The temperature, charge and strangeness dependences on the
stability of strangelet are investigated. We find that the stable strangelets
are only occured in the high strangeness and high negative charge region.Comment: 12 pages, 14 figure
Recent N^* Results From J/\psi Decays
Based on 7.8 million J/\psi events collected at BEPC, the events for J/\psi
\to p\bar{p}\pi^0 and p\bar{p}\eta have been selected and reconstructed. Clear
peaks are observed around 1480 MeV in p\pi^0 (\bar{p}\pi^0) invariant mass
spectrum and near the threshold for production in p\eta(\bar{p}\eta)
invariant mass spectrum. A partial wave analysis of J/\psi \to p\bar{p}\eta
data has been performed. Two J^P={1/2}^- resonances are observed with mass and
width (M, \Gamma) at (1540^{+15}_{-17}, 178^{+20}_{-22}) MeV and
(1648^{+18}_{-16}, 150)MeV, and are considered to be the nucleon resonances
S_{11}(1535) and S_{11}(1650) respectively.Comment: 4 pages, 4 figures, proceedings for Hadron9
Charge and critical density of strange quark matter
The electric charge of strange quark matter is of vital importance to
experiments. A recent investigation shows that strangelets are most likely
highly negatively charged, rather than slightly positively charged as
previously believed. Our present study indicates that negative charges can
indeed lower the critical density, and thus be favorable to the experimental
searches in heavy ion collisions. However, too much negative charges can make
it impossible to maintain flavor equilibrium.Comment: 4 pages, LATeX with REVTeX style, one PS figure. To be published in
Phys. Rev. C 59(6), 199
The hadron-quark phase transition in dense matter and neutron stars
We study the hadron-quark phase transition in the interior of neutron stars
(NS's). We calculate the equation of state (EOS) of hadronic matter using the
Brueckner-Bethe-Goldstone formalism with realistic two-body and three-body
forces, as well as a relativistic mean field model. For quark matter we employ
the MIT bag model constraining the bag constant by using the indications coming
from the recent experimental results obtained at the CERN SPS on the formation
of a quark-gluon plasma. We find necessary to introduce a density dependent bag
parameter, and the corresponding consistent thermodynamical formalism. We
calculate the structure of NS interiors with the EOS comprising both phases,
and we find that the NS maximum masses fall in a relatively narrow interval,
. The precise value of the
maximum mass turns out to be only weakly correlated with the value of the
energy density at the assumed transition point in nearly symmetric nuclear
matter.Comment: 25 pages, Revtex4, 16 figures included as postscrip
Chiral Relaxation Time at the Crossover of Quantum Chromodynamics
International audienceWe study microscopic processes responsible for chirality flips in the thermal bath of Quantum Chromodynamics at finite temperature and zero baryon chemical potential. We focus on the temperature range where the crossover from chirally broken phase to quark-gluon plasma takes place, namely T≃(150,200) MeV. The processes we consider are quark-quark scatterings mediated by collective excitations with the quantum number of pions and σσ-meson, hence we refer to these processes simply as one-pion (one-σ) exchange. We use a Nambu-Jona-Lasinio model to compute equilibrium properties of the thermal bath, as well as the relevant scattering kernel to be used in the collision integral to estimate the chiral relaxation time ττ. We find τ≃0.1÷1 fm/c around the chiral crossover
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