[en] N_f = 2 lattice QCD with massless quarks and a weak 4-fermion interaction appears to have the expected second order transition, at least for N_t ≥ 6. More work is needed to clarify the N_t = 4 case. With more statistics the N_t = 6 simulations should produce an accurate determination of the critical exponent β_m. Moving to finite mass at β = β_c should allow an accurate determination of σ. Hadronic screening masses need further analysis. Other order parameters remain to be analyzed. Unfortunately, there is no obvious way to include 4-fermion interactions with full SU(2) x SU(2) chiral flavor symmetry

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[en] We simulate lattice QCD at a finite chemical potential μ_I for isospin (I₃) at zero and finite temperatures. At some μ_I = μc QCD has a second order transition with mean-field critical exponents to a state where (I₃) is broken spontaneously by a charged pion condensate. Heating the system with μ_I > μ_c we find there is some temperature at which this condensate evaporates. This transition appears to be second order and mean-field at lower μ_I values, and first order for μ_I sufficiently large. We are determining the dependence of the finite temperature crossover T_c on μ_I for μ_I < μ_c. This is expected to be identical to T_c's dependence on quark-number chemical potential μ_q for small μ_q

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[en] We obtain the ratio R₁/R/sub 1/2/ of chiral symmetry breaking scales for quarks in the l = 1 and l = 1/2 representations of SU(2). (anti psi psi) is computed for the zero temperature theory in the quenched approximation on a 10⁴ lattice and the value R₁/R/sub 1/2/ = 6.6 +- 1.0 is extracted. This result is consistent with a previous estimate of the ratio of relevant scales which compared the chiral symmetry restoration temperatures T₁ and T/sub 1/2/ for the two representations and found T₁/T/sub 1/2/ = 8.6 +- 4.5. The new l = 1 data scales according to asymptotic freedom. 9 references

[en] QCD at a finite quark-number chemical potential μ has a complex fermion determinant, which precludes its study by standard lattice QCD simulations. We therefore simulate lattice QCD at finite μ in the phase-quenched approximation, replacing the fermion determinant with its magnitude. (The phase-quenched approximation can be considered as simulating at finite isospin chemical potential 2μ for N_f/2 u-type and N_F/2 d-type quark flavors.) These simulations are used to study the finite-temperature transition for small μ, where there is some evidence that the position (and possibly the nature) of this transition is unchanged by this approximation. We look for the expected critical endpoint for 3-flavor QCD. Here, it has been argued that the critical point at zero μ would become the critical endpoint at small μ, for quark masses just above the critical mass. Our simulations indicate that this does not happen, and there is no such critical endpoint for small μ. We discuss how we might adapt techniques used for imaginary μ to improve the signal/noise ratio and strengthen our conclusions, using results from relatively low statistics studies

[en] We have simulated lattice QCD with 2 flavors of massless staggered quarks. An irrelevant chiral 4-fermion interaction was added to the standard quark action to allow us to simulate at zero quark mass. Thermodynamics was studied on lattices of temporal extent 6. Clear evidence for a second order chiral transition was observed and the critical exponents β_mag, {delta}, ν and γ_mag were measured. These exponents do not agree with those expected by standard universality arguments. They are, however, consistent with tricritical behavior. The π and σ screening masses were measured and show clear evidence for chiral symmetry restoration at this transition

[en] We simulate two-flavour lattice QCD with at a finite chemical potential μ_I for isospin, and finite temperature. At small μ_I, we determine the position of the crossover from hadronic matter to a quark-gluon plasma as a function of μ_I. At larger μ_I we observe the phase transition from the superfluid pion-condensed phase to a quark-gluon plasma, noting its change from second order to first order as μ_I is increased. We also simulate two-flavour lattice QCD at zero quark mass, using an action which includes an additional 4-fermion interaction, at temperatures close to the chiral transition on N_t=8 lattices