D.K. Sinclair

Towards the continuum limit of the thermodynamics of lattice QCD with a realistic quark spectrum

Abstract Lattice QCD with a light isodoublet and a heavier strange quark is simulated on a 6 × 12 3 lattice. Metastability studies on the 6 × 12 3 lattice give considerably weaker evidence for a first order transition than on a 4 × 8 3 lattice. Comparison of chiral condensates and energy densities with similar measurements on 4 × 8 3 and 4 × 12 3 lattices also indicate that the quark-gluon plasma transition becomes less abrupt as the lattice size increases and could be just a crossover phenomenon at the quark masses simulated here. The light quark and strange quark energy densities are suppressed in the transition region and approach their high temperature limits from below.

Quenched lattice QCD at finite isospin density and related theories

We study quenched QCD at finite chemical potential

Improved staggered quark actions with reduced flavor symmetry violations for lattice QCD

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The phase diagram of four flavor SU(2) lattice gauge theory at nonzero chemical potential and temperature

for the third component of isospin and quenched two-color QCD at finite chemical potential

Diquark condensation at nonzero chemical potential and temperature

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SU(2) and SU(3) lattice gauge theories with many fermions

for quark number. In contrast with the quenched approximation to QCD at finite quark-number chemical potential, the quenched approximations to these theories behave similarly to the full theories. The reason is that these theories have real positive fermion determinants. In both of these theories there is some critical chemical potential above which the charge coupled to the chemical potential is spontaneously broken. In each case, the transition appears to be second order. We study the scaling properties near the critical point using scaling functions suggested by effective (chiral) Lagrangians and find evidence for scaling with mean-field critical exponents in each case. The subtleties associated with observing the critical scaling of these theories are discussed.

Topology, fermionic zero modes and flavor singlet correlators in finite temperature QCD

We introduce a new class of actions for staggered quarks in lattice QCD which significantly reduce flavor symmetry violations in the pion mass spectrum. An action introduced by the MILC Collaboration for the same purpose is seen to be a special case. We discuss how such actions arise from a systematic attempt to reduce flavor symmetry violations in the weak coupling limit. It is shown that for quenched lattice QCD at 6/g{sup 2}=5.7, representative actions of this class give a considerable reduction in flavor symmetry violation over the standard staggered action, and a significant reduction over what is achieved by the MILC action. {copyright} {ital 1998} {ital The American Physical Society}

Quarkonium decay matrix elements from quenched lattice QCD

Abstract SU(2) lattice gauge theory with four flavors of quarks is simulated at nonzero chemical potential μ and temperature T and the results are compared to the predictions of effective Lagrangians. Simulations on 164 lattices indicate that at zero T 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 T and μ are studied on 123×6 lattices. For low T, increasing μ takes the system through a line of second order phase transitions to a diquark condensed phase. Increasing T at high μ, the system passes through a line of first order transitions from the diquark phase to the quark–gluon plasma phase. Metastability is found near the first order line. Presumably, there is a tricritical point along this line of transitions. We estimate its position to be consistent with theoretical predictions.

Bottomonium decay matrix elements from lattice QCD with two light quarks

Abstract SU (2) lattice gauge theory with four flavors of quarks is studied at nonzero chemical potential μ and temperature T by computer simulation and Effective Lagrangian techniques. Simulations are done on 8 4 , 8 3 ×4 and 12 3 ×6 lattices and the diquark condensate, chiral order parameter, Wilson line, fermion energy and number densities are measured. Simulations at a fixed, nonzero quark mass provide evidence for a tricritical point in the μ – T plane associated with diquark condensation. For low T , increasing μ takes the system through a line of second order phase transitions to a diquark condensed phase. Increasing T at high μ , the system passes through a line of first order transitions from the diquark phase to the quark–gluon plasma phase. Using Effective Lagrangians we estimate the position of the tricritical point and ascribe its existence to trilinear couplings that increase with μ and T .

Hadron spectra and potential screening for lattice QCD with dynamical quarks

SU(2) and SU(3) lattice gauge theories are simulated by molecular dynamics methods with Nf=8 and 12 flavors of light quarks on lattices of sizes 44, 64 and 84. On the small lattices, 44 and 64, the microcanonical algorithm generates van der Waals S-shaped curves for the observables 〈ΨΨ〉, the average plaquette and the Wilson line indicating the presence of first-order phase transitions. On the 84 lattice a transition in the chiral order parameter 〈ΨΨ〉 occurs at a coupling distinct from the coupling where the Wilson line departs from zero. This suggests that these theories have a bulk, zero temperature chiral-restoring transition in addition to a rich finite temperature phase structure.