Quark-Antiquark Forces From SU(2) and SU(3) Gauge Theories on Large Lattices

We present results on the spin-independent quark-antiquark potential in SU(3) gauge theory from a simulation on a 48^3*64 lattice at Beta = 6.8, corresponding to a volume of (1.7 fm)^3. Moreover, a comprehensive analysis of spin- and velocity-dependent potentials is carried out for SU(2) gauge theory, with emphasis on the short range structure, on lattices with resolutions ranging from .02 fm to .04 fm.Comment: 10 pages, uucompressed latex with 5 ps figures, epsf style require

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

Robust functional principal components: A projection-pursuit approach

In many situations, data are recorded over a period of time and may be regarded as realizations of a stochastic process. In this paper, robust estimators for the principal components are considered by adapting the projection pursuit approach to the functional data setting. Our approach combines robust projection-pursuit with different smoothing methods. Consistency of the estimators are shown under mild assumptions. The performance of the classical and robust procedures are compared in a simulation study under different contamination schemes.Comment: Published in at http://dx.doi.org/10.1214/11-AOS923 the Annals of Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical Statistics (http://www.imstat.org

Lattice simulations with Nf=2+1N_f=2+1 improved Wilson fermions at a fixed strange quark mass

The explicit breaking of chiral symmetry of the Wilson fermion action results in additive quark mass renormalization. Moreover, flavour singlet and non-singlet scalar currents acquire different renormalization constants with respect to continuum regularization schemes. This complicates keeping the renormalized strange quark mass fixed when varying the light quark mass in simulations with $N_f=2+1$ sea quark flavours. Here we present and validate our strategy within the CLS (Coordinated Lattice Simulations) effort to achieve this in simulations with non-perturbatively order-$a$ improved Wilson fermions. We also determine various combinations of renormalization constants and improvement coefficients.Comment: 18 pages, 11 Figures, V2: References added/updated, all fits rerun with improved statistics for ensemble N204, also using the final values for the improvement coefficients A and b_P-b_A (very minor impact), The figures have been replotted accordingly. (The differences with respect to V1 are invisible to the human eye). Minor change

The Spatial String Tension in the Deconfined Phase of the (3+1)-Dimensional SU(2) Gauge Theory

We present results of a detailed investigation of the temperature dependence of the spatial string tension in SU(2) gauge theory. We show, for the first time, that the spatial string tension is scaling on the lattice and thus is non-vanishing in the continuum limit. It is temperature independent below Tc and rises rapidly above. For temperatures larger than 2Tc we find a scaling behaviour consistent with sigma_s(T) = 0.136(11) g^4(T) T^2, where g(T) is the 2-loop running coupling constant with a scale parameter determined as Lambda_T = 0.076(13) Tc.Comment: 8 pages (Latex, shell archive, 3 PostScript figures), HLRZ-93-43, BI-TP 93/30, FSU-SCRI-93-76, WUB 93-2

String breaking in Lattice QCD

The separation of a heavy quark and antiquark pair leads to the formation of a tube of flux, or string, which should break in the presence of light quark-antiquark pairs. This expected zero temperature phenomenon has proven elusive in simulations of lattice QCD. We present simulation results that show that the string does break in the confining phase at nonzero temperature.Comment: LATTICE98(hightemp), 3 pages, 4 figures, LaTe

A fresh look on the flux tube in Abelian-projected SU(2) gluodynamics

We reconsider the properties of the $Q\bar{Q}$ flux tube within Abelian-projected SU(2) lattice gauge theory in terms of electric field and monopole current. In the maximal Abelian gauge we assess the influence of the Gribov copies on the apparent flux-tube profile. For the optimal gauge fixing we study the independence of the profile on the lattice spacing for $\beta=$ 2.3, 2.4, and 2.5115 on a $32^4$ lattice. We decompose the Abelian Wilson loop into monopole and photon parts and compare the electric and monopole profile emerging from different sources with the field strength and monopole current within the dual Ginzburg-Landau theory.Comment: 3 pages, 6 figures, Lattice2002(topology

Light Hadron Spectroscopy: Theory and Experiment

Rapporteur talk at the Lepton-Photon Conference, Rome, July 2001: reviewing the evidence and strategies for understanding scalar mesons, glueballs and hybrids, the gluonic Pomeron and the interplay of heavy flavours and light hadron dynamics. Dedicated to the memory of Nathan Isgur, long-time collaborator and friend, whose original ideas in hadron spectroscopy formed the basis for much of the talk.Comment: to be published in "Lepton Photon 2001 Conference Proceedings" (World Scientific Publishing), 19 pages with 6 figure