The Non-Perturbative O(g6){\cal O}(g^6) Contribution to the Free Energy of Hot SU(N) Gauge Theory

The non-perturbative input necessary for the determination of the ${\cal O}(g^6)$ part of the weak coupling expansion of the free energy density for SU(2) and SU(3) gauge theories is estimated. Although the perturbative information completing the contribution to this order is missing, we give arguments that the magnetic fluctuations are dominated by screened elementary magnetic gluons.Comment: Talk presented at LATTICE96(finite temperature) 3 pages Latex2e, 3 ps figures, 14 k

SU(3) Gauge Theory with Adjoint Fermions

We analyze the finite temperature phase diagram of QCD with fermions in the adjoint representation. The simulations performed with four dynamical Majorana fermions, which is equivalent to two Dirac fermions, show that the deconfinement and chiral phase transitions occur at two distinct temperatures, $T_{\rm chiral} \simeq 6.65 T_{\rm deconf}$. While the deconfinement transition is first order we find evidence for a continuous chiral transition. We also present potentials for $T<T_{\rm deconf}$ and $T_{\rm deconf}<T< T_{\rm chiral}$ both for fundamental and adjoint fermion-antifermion pairs.Comment: LATTICE98(hightemp), 3 pages LaTeX2e, espcrc2 style, 6 eps figure

A Study of Finite Temperature Gauge Theory in (2+1) Dimensions

We determine the critical couplings and the critical exponents of the finite temperature transition in SU(2) and SU(3) pure gauge theory in (2+1) dimensions. We also measure Wilson loops at $T=0$ on a wide range of $\beta$ values using APE smearing to improve the signal. We extract the string tension $\sigma$ from a fit to large distances, including a string fluctuation term. With these two entities we calculate $T_c/\sqrt{\sigma}$.Comment: Talk presented at LATTICE96(finite temperature), not espcrc2 style: 7 pages, 4 ps figures, 22 k

The string tension in SU(N) gauge theory from a careful analysis of smearing parameters

We report a method to select optimal smearing parameters before production runs and discuss the advantages of this selection for the determination of the string tension.Comment: Contribution to Lat97 poster session, title was 'How to measure the string tension', 3 pages, 5 colour eps figure

Three-Dimensional SU(3) gauge theory and the Spatial String Tension of the (3+1)-Dimensional Finite Temperature SU(3) Gauge Theory

We establish a close relation between the spatial string tension of the (3+1)-dimensional $SU(3)$ gauge theory at finite temperature ($\sigma_s$) and the string tension of the 3-dimensional $SU(3)$ gauge theory ($\sigma_3$) which is similar to what has been found previously for $SU(2)$. We obtain $\sqrt{\sigma_3} = (0.554 \pm 0.004) g_3^2$ and $\sqrt{\sigma_s} = (0.586 \pm 0.045)g^2(T) T$, respectively. For temperatures larger than twice the critical temperature results are consistent with a temperature dependent coupling running according to the two-loop $\beta$-function with $\Lambda_T = 0.118(36)T_c$.Comment: 11 pages (4 figures

Thermodynamics of Four-Flavour QCD with Improved Staggered Fermions

We have calculated the pressure and energy density in four-flavour QCD using improved fermion and gauge actions. We observe a strong reduction of finite cut-off effects in the high temperature regime, similar to what has been noted before for the SU(3) gauge theory. Calculations have been performed on $16^3\times 4$ and 16^4 lattices for two values of the quark mass, $ma = 0.05$ and 0.1. A calculation of the string tension at zero temperature yields a critical temperature $T_c/\sqrt{\sigma} = 0.407 \pm 0.010$ for the smaller quark mass value.Comment: 12 pages, LaTeX2e File, 11 encapsulated postscript file

Decrease of the homogeneous width of the Tm3+ electron energy levels in TmBa2CCu3 O6+x at the superconducting transition

Enhanced NMR of 169Tm (I= 1 2) enhanced NMR has been studied in TmBa2Cu3O6+x, x=0, 0.2, 0.4, at temperatures 1.2-40K. The nuclear magnetic relaxation rates at T>20K increase exponentially as 1 T1(2) = R1(2)exp(-Δ/kT), with Δ = 176 K being the energy of the first excited state of the Tm3+ ion, while the R1(2) pre-exponential factors are inversely proportional to the homogenous width Γo of this doublet state. The pre-exponential factors measured at the frequencies of 48 and 69 MHz show homogeneous broadening of the 4f-levels due to the decreasing dipole-dipole transfer of the electron excitations from ion to ion at increasing because of crystal structure disordering. A sharp decrease of Γo (by about 0.9K) is observed in the superconducting compound with x=0.4 (Tc onset at 20K) at low temperatures and is attributed to the weakening of the 4f-electron-phonon interaction. At the temperatures around 6K the same sample displays enhancement of the transverse relaxation due to the relatively slow (W ≈ 109s-1) fluctuations of the internal magnetic fields caused by Cu2+ ions in CuO2 planes. © 1992

The O(g6){\cal O}(g^6) coefficient in the thermodynamic potential of hot SU(N) Gauge Theories and MQCD

The non-perturbative input necessary for the determination of the ${\cal O}(g^6)$ part of the weak coupling expansion of the free energy density for SU(2) and SU(3) gauge theories is estimated. Although the perturbative information completing the contribution to this order is missing, we give arguments that the magnetic fluctuations are dominated by screened elementary magnetic gluons.Comment: 15 pages, LaTeX2e File, 2 Encapsulated Postscript figure

NMR studies of singlet-ground-state rare-earth ions in high-Tc superconductors

Many of presently known high-Tc superconductors contain rare-earth (RE) ions with an even number of electrons in an unfilled 4f-shell (Pr3+, Tb3+, Ho3+, Tm3+). If the ground state of 4f-electrons is non-degenerate and separated from excited states by high enough energy intervals, one can observe the so-called "enhanced NMR" of RE nuclei at low temperatures. In the present paper some aspects of the enhanced NMR are analyzed in applications to the crystal and electron structure of high-Tc superconductors. © 1992 Springer

Heavy Quark Potentials in Quenched QCD at High Temperature

Heavy quark potentials are investigated at high temperatures. The temperature range covered by the analysis extends from $T$ values just below the deconfinement temperature up to about $4 T_c$ in the deconfined phase. We simulated the pure gauge sector of QCD on lattices with temporal extents of 4, 6 and 8 with spatial volumes of $32^3$. On the smallest lattice a tree level improved action was employed while in the other two cases the standard Wilson action was used. Below $T_c$ we find a temperature dependent logarithmic term contributing to the confinement potential and observe a string tension which decreases with rising temperature but retains a finite value at the deconfinement transition. Above $T_c$ the potential is Debye-screened, however simple perturbative predictions do not apply.Comment: 20 pages, 9 figure