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Alexei Bazavov

Publications and source records attributed to Alexei Bazavov.

70 records · Page 4Linked to original sources

First results on QCD thermodynamics with HISQ action

We report on investigations of the chiral and deconfinement aspects of the finite temperature transition in 2+1 flavor QCD using the Highly Improved Staggered Quark (HISQ) action on lattices with temporal extent $N_τ=6$ and $N_τ=8$. We have calculated several physical observables, including the renormalized Polyakov loop, strangeness fluctuations, the renormalized chiral condensate and the chiral susceptibility in the crossover region for physical values of the strange quark mass $m_s$ and light quark masses $m_l=0.2m_s$ and $0.05m_s$. We compare our findings with previous calculations that use different improved staggered fermion formulations: asqtad, p4 and stout.

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Deconfining phase transition on a double-layered torus

Deconfined regions in relativistic heavy ion collisions are limited to small volumes surrounded by a confined exterior. Here the geometry of a double layered torus is discussed, which allows for different temperatures in its two layers. This geometry enables one to approach the QCD continuum limit for small deconfined volumes with confined exteriors in a more realistic fashion than by using periodic boundary conditions. Preliminary data from a study for pure SU(3) lattice gauge theory support a substantial increase in a pseudo transition temperature.

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Quarkonium at Finite Temperature

We discuss properties of heavy quarkonium states at high temperatures based on lattice QCD and potential models. We review recent progress made in lattice calculations of spatial static quark anti-quark correlators as well as quarkonium correlators in Euclidean time. Recent developments in effective field theory approach and potential models are also discussed.

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Program package for multicanonical simulations of U(1) lattice gauge theory

We document our Fortran 77 code for multicanonical simulations of 4D U(1) lattice gauge theory in the neighborhood of its phase transition. This includes programs and routines for canonical simulations using biased Metropolis heatbath updating and overrelaxation, determination of multicanonical weights via a Wang-Landau recursion, and multicanonical simulations with fixed weights supplemented by overrelaxation sweeps. Measurements are performed for the action, Polyakov loops and some of their structure factors. Many features of the code transcend the particular application and are expected to be useful for other lattice gauge theory models as well as for systems in statistical physics.

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Color singlet and adjoint free energy at finite temperature

We study correlation functions of static quark-antiquark pairs in SU(2) gauge theory at finite temperature. By measuring Polyakov loop correlators and temporal Wilson loops with APE smearing of spatial links we are able to give consistent definitions of the singlet and adjoint free energies at short distances, where the notion of these free energies is meaningful. APE smearing procedure allows to achieve a high degree of overlap in the singlet channel and to reconstruct the adjoint part from the color averaged and singlet free energy.

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Phase Transition Properties of 3D Potts Models

Using multicanonical Metropolis simulations we estimate phase transition properties of 3D Potts models for q=4 to 10: The transition temperatures, latent heats, entropy gaps, normalized entropies at the disordered and ordered endpoints, interfacial tensions, and spinodal endpoints.

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Thermalization in SU(3) gauge theory after a deconfining quench

We determine the time evolution of fluctuations of the Polyakov loop after a quench into the deconfined phase of SU(3) gauge theory from a simple classical relativistic Lagrangian. We compare the structure factors, which indicate spinodal decomposition followed by relaxation, to those obtained via Markov Chain Monte Carlo techniques in SU(3) lattice gauge theory. We find that the time when the structure factor peaks diverges like $\sim 1/k^2$ in the long-wavelength limit. This is due to formation of competing Z(3) domains for configurations where the Polyakov loop exhibits non-perturbatively large variations in space, which delay thermalization of long wavelength modes. For realistic temperatures, and away from the extreme weak-coupling limit, we find that even modes with $k$ on the order of $T$ experience delayed thermalization. Relaxation times of very long wavelength modes are found to be on the order of the size of the system; thus, the dynamics of competing domains should accompany the hydrodynamic description of the deconfined vacuum.

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SU(3) Deconfining Phase Transition in a Box with Cold Boundaries

Deconfined regions created in heavy ion collisions are bordered by the confined phase. We discuss boundary conditions (BCs) to model a cold exterior. Monte Carlo simulations of pure SU(3) lattice gauge theory with thus inspired BCs show scaling. Corrections to usual results survive in the finite volume continuum limit and we estimate them in a range from L=5-10 fermi as function of the volume size $L^3$. In magnitude these corrections are comparable to those obtained by including quarks.

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Deconfining Phase Transition on Lattices with Boundaries at Low Temperature

In lattice gauge theory (LGT) equilibrium simulations of QCD are usually performed with periodic boundary conditions (BCs). In contrast to that deconfined regions created in heavy ion collisions are bordered by the confined phase. Here we discuss BCs in LGT, which model a cold exterior of the lattice volume. Subsequently we perform Monte Carlo (MC) simulations of pure SU(3) LGT with a thus inspired simple change of BCs using volumes of a size comparable to those typically encountered in the BNL relativistic heavy ion collider (RHIC) experiment. Corrections to the usual LGT results survive in the finite volume continuum limit and we estimate them as function of the volume size. In magnitude they are found comparable to those of including quarks. As observables we use a pseudocritical temperature, which rises opposite to the effect of quarks, and the width of the transition, which broadens similar to the effect of quarks.

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Normalized entropy density of the 3D 3-state Potts model

Using a multicanonical Metropolis algorithm we have performed Monte Carlo simulations of the 3D 3-state Potts model on $L^3$ lattices with L=20, 30, 40, 50. Covering a range of inverse temperatures from $β_{\min}=0$ to $β_{\max}=0.33$ we calculated the infinite volume limit of the entropy density $s(β)$ with its normalization obtained from $s(0)=\ln 3$. At the transition temperature the entropy and energy endpoints in the ordered and disordered phase are estimated employing a novel reweighting procedure. We also evaluate the transition temperature and the order-disorder interface tension. The latter estimate increases when capillary waves are taken into account.

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Non-Perturbative U(1) Gauge Theory at Finite Temperature

For compact U(1) lattice gauge theory (LGT) we have performed a finite size scaling analysis on $N_τ N_s^3$ lattices for $N_τ$ fixed by extrapolating spatial volumes of size $N_s\le 18$ to $N_s\to\infty$. Within the numerical accuracy of the thus obtained fits we find for $N_τ=4$, 5 and~6 second order critical exponents, which exhibit no obvious $N_τ$ dependence. The exponents are consistent with 3d Gaussian values, but not with either first order transitions or the universality class of the 3d XY model. As the 3d Gaussian fixed point is known to be unstable, the scenario of a yet unidentified non-trivial fixed point close to the 3d Gaussian emerges as one of the possible explanations.

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Critical Exponents for U(1) Lattice Gauge Theory at Finite Temperature

For compact U(1) lattice gauge theory (LGT) we have performed a finite size scaling analysis on $N_τ N_s^3$ lattices for $N_τ$ fixed and $N_s\to\infty$, approaching the phase transition from the confined phase. For $N_τ=4$, 5 and 6 our data contradict the expected scenario that this transition is either first order or in the universality class of the 3d XY model. If there are no conceptional flaws in applying the argument that the Gaussian fixed point in 3d is unstable to our systems, estimates of the critical exponents $α/ν$, $γ/ν$, $(1-β)/ν$ and $2-η$ indicate the existence of a new, non-trivial renormalization group fixed point for second order phase transitions in 3d. Such a fixed point would be of importance for renormalization group theory and statistical physics.

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Glauber dynamics of phase transitions: SU(3) lattice gauge theory

Motivated by questions about the QCD deconfining phase transition, we studied in two previous papers Model A (Glauber) dynamics of 2D and 3D Potts models, focusing on structure factor evolution under heating (heating in the gauge theory notation, i.e., cooling of the spin systems). In the present paper we set for 3D Potts models (Ising and 3-state) the scale of the dynamical effects by comparing to equilibrium results at first and second order phase transition temperatures, obtained by re-weighting from a multicanonical ensemble. Our finding is that the dynamics entirely overwhelms the critical and non-critical equilibrium effects. In the second half of the paper we extend our results by investigating the Glauber dynamics of pure SU(3) lattice gauge on $N_τ N_σ^3$ lattices directly under heating quenches from the confined into the deconfined regime. The exponential growth factors of the initial response are calculated, which give Debye screening mass estimates. The quench leads to competing vacuum domains of distinct $Z_3$ triality, which delay equilibration of pure gauge theory forever, while their role in full QCD remains a subtle question. As in spin systems we find for pure SU(3) gauge theory a dynamical growth of structure factors, reaching maxima which scale approximately with the volume of the system, before settling down to equilibrium. Their influence on various observables is studied and different lattice sizes are simulated to illustrate an approach to a finite volume continuum limit. Strong correlations are found during the dynamical process, but not in the deconfined phase at equilibrium.

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Biased Metropolis-Heat-Bath Algorithm for Fundamental-Adjoint SU(2) Lattice Gauge Theory

For SU(2) lattice gauge theory with the fundamental-adjoint action an efficient heat-bath algorithm is not known so that one had to rely on Metropolis simulations supplemented by overrelaxation. Implementing a novel biased Metropolis-heat-bath algorithm for this model, we find improvement factors in the range 1.45 to 2.06 over conventionally optimized Metropolis simulations. If one optimizes further with respect to additional overrelaxation sweeps, the improvement factors are found in the range 1.3 to 1.8.

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Heat Bath Efficiency with Metropolis-Type Updating

We illustrate for 4D SU(2) and U(1) lattice gauge theory that sampling with a biased Metropolis scheme is essentially equivalent to using the heat bath algorithm. Only, the biased Metropolis method can also be applied when an efficient heat bath algorithm does not exist.

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Model A Dynamics and the Deconfining Phase Transition for Pure Lattice Gauge Theory

We consider model A dynamics for a heating quench from the disordered (confined) into the ordered (deconfined) phase of SU(3) lattice gauge theory. For $4 N_σ^3$ lattices the exponential growth factors of low-lying structure function modes are calculated. The linear theory of spinodal decompositions is compared with the data from an effective model and the Debye screening mass is estimated from the critical mode. Further, the quench leads to competing vacuum domains, which make the equilibration of the QCD vacuum after the heating non-trivial. We investigate the influence of such domains on the gluonic energy density.

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