12,591 research outputs found
Finite Density Fat QCD
Lattice formulation of Finite Baryon Density QCD is problematic from computer
simulation point of view; it is well known that for light quark masses the
reconstructed partition function fails to be positive in a wide region of
parameter space. For large bare quark masses, instead, it is possible to obtain
more sensible results; problems are still present but restricted to a small
region. We present evidence for a saturation transition independent from the
gauge coupling and for a transition line that, starting from the
temperature critical point at , moves towards smaller with
increasing as expected from simplified phenomenological arguments.Comment: 14 pages, 10 figure
Hadronic property at finite density
We report on three topics on finite density simulations: (i) the derivative
method for hadronic quantities, (ii) phase fluctuations in the vicinity of the
critical temperature and (iii) the density of states method at finite isospin
density.Comment: 11 pages, 11 figures, talk given at Finite Density QCD, at Nara,
Japan 10-12 July 200
Frustration in Finite Density QCD
We present a detailed analysis of the QCD partition function in the Grand
Canonical formalism. Using the fugacity expansion we find evidence for
numerical instabilities in the standard evaluation of its coefficients. We
discuss the origin of this problem and propose an issue to it. The correct
analysis shows no evidence for a discontinuity in the baryonic density in the
strong coupling limit. The moderate optimism that was inspired by the Grand
Canonical Partition Function calculations in the last years has to be
considered ill-founded.Comment: 9 pages, 6 Postscript figures; some comments adde
Pion properties at finite density
In this talk, we report our recent work on the pion weak decay constant
(F_pi) and pion mass (m_pi) using the nonlocal chiral quark model with the
finite quark-number chemical potential (mu) taken into account. Considering the
breakdown of Lorentz invariance at finite density, the time and space
components are computed separately, and the corresponding results turn out to
be: F^t_pi = 82.96 MeV and F^s_pi = 80.29 MeV at mu_c ~ 320 MeV, respectively.
Using the in-medium Gell-Mann Oakes-Renner (GOR) relation, we show that the
pion mass increases by about 15% at mu_c.Comment: 5 pages, 2 figures, Talk given at the 4th Asia-Pacific Conference on
Few-Body Problems in Physics 2008 (APFB08), 19 ~ 23 Aug 2008, Depok,
Indonesi
Field Redefinitions at Finite Density
The apparent dependence of nuclear matter observables on off-shell properties
of the two-nucleon potential is re-examined in the context of the effective
field theory (EFT) approach. Finite density (thermodynamic) observables are
invariant under field redefinitions, which extends the well-known theorem about
the invariance of S-matrix elements. Simple examples demonstrate how field
redefinitions can shift contributions between purely off-shell two-body
interactions and many-body forces, leaving both scattering and finite-density
observables unchanged. If only the transformed two-body potentials are kept,
however, the nuclear matter binding curves will depend on the off-shell part
(generating ``Coester bands''). The correspondence between field redefinitions
and unitary transformations, which have traditionally been used to generate
``phase-equivalent'' nucleon-nucleon potentials, is also demonstrated.Comment: 23 pages, RevTex, 9 ps figures, included with epsf.tex, minor change
Lattice QCD at Finite Density
I discuss different approaches to finite density lattice QCD. In particular,
I focus on the structure of the phase diagram and discuss attempts to determine
the location of the critical end-point. Recent results on the transiton line as
function of the chemical potential () are reviewed. Along the
transition line, hadronic fluctuations have been calculated, which can be used
to characterize properties of the Quark Gluon plasma and eventually can also
help to identify the location of the critical end-point in the QCD phase
diagram on the lattice and in heavy ion experiments. Furthermore, I comment on
the structure of the phase diagram at large .Comment: Plenary talk at XXIVth International Symposium on Lattice Field
Theory (Lattice 2006). Version to appear as PoS (LAT2006) 021; references
adde
Lattice QCD at finite density
QCD at finite density presents specific challenges to lattice gauge theory.
Nonetheless, a region of the QCD phase diagram up to moderately large baryon
chemical potentials has been successfully explored on the lattice and new
results and idea are continuously emerging.
I will outline the lattice formulation of QCD, introduce the calculational
schemes currently used to treat a nonzero baryon density, and mention lattice
methods alternative to MonteCarlo, including the strong coupling expansion
which might give access to the the superconducting phase of QCD. The results
for the critical line, and the different phases will be discussed highlighting
the strength of the different methods, as well as the possible comparisons with
phenomenological models.Comment: 14 pages; to appear in the proceedings of Workshop on Finite Density
QCD at Nara, Nara, Japan, 10-12 July 200
Results on Finite Density QCD
A brief summary of the formulation of QCD at finite chemical potental, ,
is presented. The failure of the quenched approximation to the problem is
reviewed.
Results are presented for dynamical simulations of the theory at strong and
intermediate couplings. We find that the problems associated with the quenched
theory persist: the onset of non-zero quark number does seem to occur at a
chemical potential . However analysis of the
Lee-Yang zeros of the grand canonical partition function in the complex
fugacity plane, (), does show signals of critical behaviour in the
expected region of chemical potential.
Results are presented for a simulation at finite density of the Gross-Neveu
model on a lattice near to the chiral limit. Contrary to our simulations
of QCD no pathologies were found when passed through the value
m_{\pi}/2}.Comment: 14 pages, Latex, 18 eps figures, Review for Tsukuba worksho
Chiral Lagrangians at finite density
The effective SU(2) chiral Lagrangian with external sources is given in the
presence of non-vanishing nucleon densities by calculating the in-medium
contributions of the chiral pion-nucleon Lagrangian. As a by product, a
relativistic quantum field theory for Fermi many-particle systems at zero
temperature is directly derived from relativistic quantum field theory with
functional methods.Comment: 6 Pages, 3 figures, REVTeX. Extended version. Explicit Feynman rules
are give
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