6 research outputs found
Constraining the QCD phase diagram by tricritical lines at imaginary chemical potential
We present unambiguous evidence from lattice simulations of QCD with three
degenerate quark species for two tricritical points in the (T,m) phase diagram
at fixed imaginary \mu/T=i\pi/3 mod 2\pi/3, one in the light and one in the
heavy mass regime. These represent the boundaries of the chiral and
deconfinement critical lines continued to imaginary chemical potential,
respectively. It is demonstrated that the shape of the deconfinement critical
line for real chemical potentials is dictated by tricritical scaling and
implies the weakening of the deconfinement transition with real chemical
potential. The generalization to non-degenerate and light quark masses is
discussed.Comment: 4 pages, 5 figure
Towards a controlled study of the QCD critical point
The phase diagram of QCD, as a function of temperature T and quark chemical
potential mu, may contain a critical point (mu_E,T_E) whose non-perturbative
nature makes it a natural object of lattice studies. However, the sign problem
prevents the application of standard Monte Carlo techniques at non-zero baryon
density. We have been pursuing an approach free of the sign problem, where the
chemical potential is taken as imaginary and the results are Taylor-expanded in
mu/T about mu=0, then analytically continued to real mu.
Within this approach we have determined the sensitivity of the critical
chemical potential mu_E to the quark mass, d(\mu_E)^2/dm_q|_{\mu_E=0}. Our
study indicates that the critical point moves to {\em smaller} chemical
potential as the quark mass {\em increases}. This finding, contrary to common
wisdom, implies that the deconfinement crossover, which takes place in QCD at
mu=0 when the temperature is raised, will remain a crossover in the mu-region
where our Taylor expansion can be trusted. If this result, obtained on a coarse
lattice, is confirmed by simulations on finer lattices now in progress, then we
predict that no {\em chiral} critical point will be found for mu_B \lesssim 500
MeV, unless the phase diagram contains additional transitions.Comment: 4 pages, 6 figures, proceedings of Quark Matter 2008, Jaipur (India),
Feb. 2008, to appear in J. Phys.
Progress in finite temperature lattice QCD
I review recent progress in finite temperature lattice calculations,
including the determination of the transition temperature, equation of state,
screening of static quarks and meson spectral functions.Comment: 8 pages, LaTeX, uses iopart.cls, invited talk presented at
Strangeness in Quark Matter 2007 (SQM 2007), Levoca, Slovakia, June 24-29,
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Developments in lattice quantum chromodynamics for matter at high temperature and density
A brief overview of the QCD phase diagram at nonzero temperature and density is provided. It is explained why standard lattice QCD techniques are not immediately applicable for its determination, due to the sign problem. We then discuss a selection of recent lattice approaches that attempt to evade the sign problem and classify them according to the underlying principle: constrained simulations (density of states, histograms), holomorphicity (complex Langevin, Lefschetz thimbles), partial summations (clusters, subsets, bags) and change in integration order (strong coupling, dual formulations)
QCD and strongly coupled gauge theories : challenges and perspectives
We highlight the progress, current status, and open challenges of QCD-driven physics, in theory and in experiment. We discuss how the strong interaction is intimately connected to a broad sweep of physical problems, in settings ranging from astrophysics and cosmology to strongly coupled, complex systems in particle and condensed-matter physics, as well as to searches for physics beyond the Standard Model. We also discuss how success in describing the strong interaction impacts other fields, and, in turn, how such subjects can impact studies of the strong interaction. In the course of the work we offer a perspective on the many research streams which flow into and out of QCD, as well as a vision for future developments.Peer reviewe