4,609 research outputs found
The Phase Diagram of Four Flavor SU(2) Lattice Gauge Theory at Nonzero Chemical Potential and Temperature
SU(2) lattice gauge theory with four flavors of quarks is simulated at
nonzero chemical potential and temperature and the results are
compared to the predictions of Effective Lagrangians. Simulations on
lattices indicate that at zero the theory experiences a second order phase
transition to a diquark condensate state. Several methods of analysis,
including equation of state fits suggested by Chiral Perturbation Theory,
suggest that mean-field scaling describes this critical point. Nonzero and
are studied on lattices. For low , increasing
takes the system through a line of second order phase transitions to a diquark
condensed phase. Increasing at high , the system passes through a line
of first order transitions from the diquark phase to the quark-gluon plasma
phase. Metastability is found in the vicinity of the first order line. There is
a tricritical point along this line of transitions whose position is consistent
with theoretical predictions.Comment: 42 pages revtex, 25 figures postscrip
Logarithmic Corrections to the Equation of State in the SU(2)xSU(2) Nambu - Jona-Lasinio Model
We present results from a Monte Carlo simulation of the Nambu - Jona-Lasinio
model, with continuous SU(2)xSU(2) chiral symmetry, in four Euclidean
dimensions. Different model equations of state, corresponding to different
theoretical scenarios, are tested against the order parameter data. The results
are sensitive to necessary assumptions about the shape and extent of the
scaling region. Our best fits favour a trivial scenario in which the
logarithmic corrections are qualitatively similar to those predicted by the
large N_f approximation. This is supported by a separate analysis of finite
volume corrections for data taken directly in the chiral limit.Comment: 37 pages LaTeX (RevTeX) including 12 .eps figure
Isospin Chemical Potential and the QCD Phase Diagram at Nonzero Temperature and Baryon Chemical Potential
We use the Nambu--Jona-Lasinio model to study the effects of the isospin
chemical potential on the QCD phase diagram at nonzero temperature and baryon
chemical potential. We find that the phase diagram is qualitatively altered by
a small isospin chemical potential. There are two first order phase transitions
that end in two critical endpoints, and there are two crossovers at low baryon
chemical potential. These results have important consequences for systems where
both baryon and isospin chemical potentials are nonzero, such as heavy ion
collision experiments. Our results are in complete agreement with those
recently obtained in a Random Matrix Model.Comment: 4 pages, 1 figure, REVTeX
Complex Langevin Simulations of QCD at Finite Density -- Progress Report
We simulate lattice QCD at finite quark-number chemical potential to study
nuclear matter, using the complex Langevin equation (CLE). The CLE is used
because the fermion determinant is complex so that standard methods relying on
importance sampling fail. Adaptive methods and gauge-cooling are used to
prevent runaway solutions. Even then, the CLE is not guaranteed to give correct
results. We are therefore performing extensive testing to determine under what,
if any, conditions we can achieve reliable results. Our earlier simulations at
, on a lattice reproduced the expected phase
structure but failed in the details. Our current simulations at on
a lattice fail in similar ways while showing some improvement. We are
therefore moving to even weaker couplings to see if the CLE might produce the
correct results in the continuum (weak-coupling) limit, or, if it still fails,
whether it might reproduce the results of the phase-quenched theory. We also
discuss action (and other dynamics) modifications which might improve the
performance of the CLE.Comment: Talk presented at Lattice 2017, Granada, Spain and submitted to
proceedings. 8 pages, 4 figure
- …