546 research outputs found
Strongly Coupled QCD at Finite Baryon Density
The analytical results obtained in the infinite mass and strong coupling
limits of QCD are difficult to reconcile with the predictions of the Monomer
Dimer Polymer algorithm. We have reconsidered in detail the results obtained
with this simulation scheme and evidences of severe convergence problems are
presented for the SU(3) and SU(2) gauge group.Comment: LATTICE99(Finite Temperature and Density), 3 pages, 3 postscript
figure
Finite Density QCD in the Chiral Limit
We present the first results of an exact simulation of full QCD at finite
density in the chiral limit. We have used a MFA (Microcanonical Fermionic
Average) inspired approach for the reconstruction of the Grand Canonical
Partition Function of the theory; using the fugacity expansion of the fermionic
determinant we are able to move continuously in the () plane with
.Comment: 3 pages, LaTeX, 3 figures, uses espcrc2.sty, psfig. Talk presented by
A. Galante at Lattice 97. Correction of some reference
Finite density QCD with heavy quarks
In the large fermion mass limit of QCD at finite density the structure of the
partition function greatly simplifies and can be studied analytically. We show
that, contrary to general wisdom, the phase of the Dirac determinant is
relevant only at finite temperature and can be neglected for zero temperature
fields.Comment: LATTICE98(hightemp), 3 pages, 3 figure
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
Large N Lattice QED
We study the critical behaviour of non compact QED with
species of light fermions, using a method we have proposed for unquenched
simulations. We find that there exist two phase transition lines: one, second
order, and the other, first order, that approaches asymptotically the
axis. These two lines have different physical origin, the second one being
entirely due to fermions effects. We discuss the effect of the approximation
used, in terms of an expansion of the effective action in powers of , and
conclude that the general features should not be affected by this
approximation.Comment: 9 pages. LNF 92/110
New Method for Dynamical Fermions and Chiral-Symmetry Breaking
The reasons for the feasibility of the Microcanonical Fermionic Average
() approach to lattice gauge theory with dynamical fermions are discussed.
We then present a new exact algorithm, which is free from systematic errors and
convergent even in the chiral limit.Comment: 3 pages, DFTUZ 93/20, to appear in the Proceedings of Lattice 93,
Dalla
Phase transition(s) in finite density QCD
The Grand Canonical formalism is generally used in numerical simulations of
finite density QCD since it allows free mobility in the chemical potential
. We show that special care has to be used in extracting numerical results
to avoid dramatic rounding effects and spurious transition signals. If we
analyze data correctly, with reasonable statistics, no signal of first order
phase transition is present and results using the Glasgow prescription are
practically coincident with the ones obtained using the modulus of the
fermionic determinant.Comment: 6 pages, 5 ps figs. To appear in Proceedings of "QCD at Finite Baryon
Density" workshop, Bielefeld, 27-30 April 199
Three and Two Colours Finite Density QCD at Strong Coupling: A New Look
Simulations in finite density, beta=0 lattice QCD by means of the
Monomer-Dimer-Polymer algorithm show a signal of first order transition at
finite temporal size. This behaviour agrees with predictions of the mean field
approximation, but is difficult to reconcile with infinite mass analytical
solution. The MDP simulations are considered in detail and severe convergence
problems are found for the SU(3) gauge group, in a wide region of chemical
potential. Simulations of SU(2) model show discrepancies with MDP results as
well.Comment: 18 pages, 9 figures, to appear in Nucl. Phys.
Rigorous arguments against current wisdoms in finite density QCD
QCD at finite chemical potential is analytically investigated in the region
of large bare fermion masses. We show that, contrary to the general wisdom, the
phase of the fermion determinant is irrelevant at zero temperature. However if
the system is put at finite temperature, the contribution of the phase is
finite. We also discuss on the quenched approximation and suggest that the
origin of the failure of this approximation in finite density QCD could relay
on the fundamental role that Pauli exclusion principle plays in this case.Comment: 16 pages, 5 figure
Testing logarithmic violations to scaling in strongly coupled QED
Using very precise measurements of the critical couplings for the chiral
transition of non compact with up to 8 flavours, we analyse the
behaviour of the order parameter at the critical point using the equation of
state of a logarithmically improved scalar mean field theory, that of the
Nambu-Jona Lasinio theory and a pure power law. The first case is definitively
excluded by the numerical data. The stability of the fits for the last two
cases, as well as the behaviour with the number of flavours of the exponent of
the logarithmic violations to the scaling favour clearly a pure power law
scaling with non mean field exponents.Comment: 6 pages, 3 postscript figures, 2 postscript tables (tar-ed, zip-ed,
uu-encoded
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