27966894
Fermions obstruct dimensional reduction in hot QCD
We have studied, for the first time, screening masses obtained from glueball-like correlators in quantum chromodynamics with four light dynamical flavors of quarks in the temperature range 1. 5T(c)</=T</=3T(c), where T(c) is the temperature at which the chiral transition occurs. We have also studied pionlike and sigmalike screening masses and found that they are degenerate in the entire range of T. These obstruct perturbative dimensional reduction since the lowest glueball screening mass is heavier than them. Extrapolation of our results suggests that this obstruction may affect the entire range of temperature expected to be reached even at the Large Hadron Collider.
122166973
The phase diagram of QCD: methods and logic of the comparison of experiments and theory
Abstract A small review of the phase diagram of QCD is presented. This is followed by a discussion of the conditions under which experimental data on the fluctuations of conserved quantities in heavy-ion collisions can be treated in the grand canonical ensemble. A robust method for detecting the presence of a nearby critical point in experiments is given. There is a short discussion of the need for non-Gaussian error analysis.
123004962
Flavour degrees of freedom and the transition temperature in QCD
We study the finite temperature transition in QCD with four flavours of dynamical quarks. Our simulation is performed on an 8×16 3 lattice for quarks of mass ma=0.01. At the coupling β c =5.15, we find long-lived metastable states, as well as an abrupt change in the entropy density, suggesting a first order phase transition. Using presently available results from corresponding calculations of the hadron masses and the chiral condensate, this gives us a transition temperature T c ≅100 MeV, which is a factor two lower than the transition temperature found in quenched QCD.
119431013
A precise determination of T_c in QCD from scaling
Existing lattice data on the QCD phase transition are analyzed in renormalized perturbation theory. In quenched QCD it is found that T_c scales for lattices with only 3 time slices, and that T_c/Lambda_msbar=1.15 \pm 0.05. A preliminary estimate in QCD with two flavours of dynamical quarks shows that this ratio depends on the quark mass. For realistic quark masses we estimate T_c/Lambda_msbar=0.49 \pm 0.02. We also investigate the equation of state in quenched QCD at 1-loop order in renormalised perturbation theory.
121387686
Hybrid Monte Carlo simulations of a two-dimensional gauge theory
Through a study of the dynamics of the two-dimensional U(1) pure gauge theory we find exponential slowing down in barrier penetration problems. We verify that the dynamical critical exponent in HMC can be tuned exactly to 1, and that normal and gauge fixed updates have equal cost.
17443615
Lattice QCD for RHIC
I briefly introduce the methods by which lattice QCD predictions for RHIC are obtained. Next I deal with lattice determinations of strangeness production and event-to-event fluctuations of conserved quantities. I also present a new diagrammatic method for computing derivatives with respect to chemical potentials, and conclude with discussions of some tests of thermal perturbation theory which follow.
37920331
Systematics in the volume integrals of the imaginary part of the light ion optical potentials.
A systematic analysis of the imaginary part of the light projectile (A/sub p/ = 1--6) phenomenological optical potentials has been carried out. As a result of this analysis a global formula has been found which describes successfully the volume integrals of the imaginary potential in terms of the projectile energy in the range 0--50 MeV/nucleon and the target and the projectile mass numbers.
28852253
Dealing with truncation in Monte Carlo renormalization-group calculations.
On utilise le modele d'Ising d=2 comme exemple concret pour montrer que la troncature de la matrice T derivee au sous-espace S des interactions a courte portee n'a pas besoin de justification
12480798
Critical behavior of the two-dimensional XY model.
We present detailed Monte Carlo results for the susceptibility {chi}, correlation length {xi}, and specific heat {ital C}{sub {ital v}} for the {ital XY} model. The simulations are done on 64{sup 2}, 128{sup 2}, 256{sup 2}, and 512{sup 2} lattices over the temperature range 0.98{le}{ital T}{le}1.43 corresponding to 2{lt}{xi}{lt}70. Fits to {chi} and {xi} data favor a Kosterlitz-Thouless (KT) singularity over a second-order transition; however, unconstrained four-parameter KT fits do not confirm the predicted values {nu}=0.5 and {eta}=0.25. Our best estimate, {ital T}{sub {ital c}}=0.894(5), is obtained using KT fits with {nu} fixed at 0.5. The exponent {eta} is calculated as a function of temperature in the spin-wave phase using Monte Carlo renormalization-group and finite-size-scaling methods. Both methods give consistent results and we find {eta}{approx}0.235 at {ital T}=0.894. We also present results for the behavior of vortex density across the transition and exhibit how the dilute-gas approximation breaks down.
14017597
Bethe-Salpeter amplitudes and density correlations for mesons with Wilson fermions.
We present an investigation of various gauge-invariant definitions of the qq Bethe-Salpeter (BS) amplitude for mesons in lattice QCD, and compare them to the Coulomb and Landau gauge BS amplitudes. We show that the gauge-invariant BS amplitude is considerably broadened by the use of «fat» gauge links (constructed by smearing the links of the original lattice). A qualitative demonstration of the Lorentz contraction of the pion wave function at nonzero momentum is given. We also calculate density-density correlations and discuss the limitations in extracting the charge radius of the pion from these observables. Lastly, the polarization dependence of the BS amplitude for the ρ meson is exhibited, and we extract the relative admixture of l = 0 and l = 2 states showing that simple hydrogenlike wave functions provide a good fit
1943581
Quark confinement in quantum chromodynamics.
A quark-confinement mechanism inspired by renormalization-group-improved perturbative quantum chromodynamics is proposed. We obtain a quark-antiquark confining potential in the lowest approximation, show that it yields reasonable results for the bb-bar and cc-bar spin-averaged energy levels, and comment on the significance of the higher-order effects.