Precision computation of the strange quark's mass in quenched QCD

We determine the renormalization group invariant quark mass corresponding to the sum of the strange and the average light quark mass in the quenched approximation of QCD, using as essential input the mass of the K-mesons. In the continuum limit we find (M_s+M)/F_K=0.874(29), which includes systematic errors. Translating this nonperturbative result into the running quark masses in the MS-scheme at #mu#=2 GeV and using the quark mass ratios from chiral perturbation theory, we obtain anti m_s (2 GeV)=97(4) MeV. With the help of recent results by the CP-PACS Collaboration, we estimate that a 10% higher value would be obtained if one replaced F_K by the nucleon mass to set the scale. This is a typical ambiguity in the quenched approximation. (orig.)55 refs.SIGLEAvailable from TIB Hannover: RA 2999(99-075) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Precision computation of a low-energy reference scale in quenched lattice QCD

We present results for the reference scale r_0 in SU(3) lattice gauge theory for #beta# = 6/g_0"2 in the range 5.7 #<=# #beta# #<=# 6.57. The high relative accuracy of 0.3-0.6% in r_0/a was achieved through good statistics, the application of a multi-hit procedure and a variational approach in the computation of Wilson loops. A precise definition of the force used to extract r_0 has been used throughout the calculation which guarantees that r_0/a is a smooth function of the bare coupling and that subsequent continuum extrapolations are possible. The results are applied to the continuum extrapolations of the energy gap #DELTA# in the static quark potential and the scale L_m_a_x/r_0 used in the calculation of the running coupling constant. (orig.)31 refs.Available from TIB Hannover: RA 2999(98-064) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

On the mass spectrum of the SU(2) Higgs model in 2+1 dimensions

We calculate the masses of the low-lying states with quantum numbers J"P"C=0"+"+, 1"-"- in the Higgs and confinement regions of the three-dimensional SU(2) Higgs model, which plays an important role in the description of the thermodynamic properties of the standard model at finite temperatures. We extract the masses from correlation functions of gauge-invariant operators which are calculated by means of a lattice Monte Carlo simulation. The projection properties of our lattice operators onto the lowest states are greatly improved by the use of smearing techniques. We also consider cross correlations between various operators with the same quantum numbers. From these the mass eigenstates are determined by means of a variational calculation. In the symmetric phase, we find that some of the ground state masses are about 30% lighter than those reported from previous simulations. We also obtain the masses of the first few excited states in the symmetric phase. Remarkable among these is the occurrence of a 0"+"+ state composed almost entirely of gauge degrees of freedom. The mass of this state, as well as that of its first excitations, is nearly identical to the corresponding glueball states in three-dimensional SU(2) pure gauge theory, indicating an approximate decoupling of the pure gauge sector from the Higgs sector of the model. We perform a detailed study of finite size effects and extrapolate the lattice mass spectrum to the continuum. (orig.)28 refs.Available from TIB Hannover: RA 2999(96-017) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Low energy physics from the QCD Schroedinger functional

We review recent work by the ALPHA and UKQCD Collaborations where masses and matrix elements were computed in lattice QCD using Schroedinger functional boundary conditions and where the strange quark mass was determined in the quenched approximation. We emphasize the general concepts and our strategy for the computation of quark masses. (orig.)18 refs.SIGLEAvailable from TIB Hannover: RA 2999(99-134) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Non-perturbative quark mass renormalization in quenched lattice QCD

The renormalization factor relating the bare to the renormalization group invariant quark masses is accurately calculated in quenched lattice QCD using a recursive finite-size technique. The result is presented in the form of a product of a universal factor times another factor, which depends on the details of the lattice theory but is easy to compute, since it does not involve any large scale differences. As a byproduct the #LAMBDA#-parameter of the theory is obtained with a total error of 8%. (orig.)73 refs.Available from TIB Hannover: RA 2999(98-154) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman