Measuring the interface tension when the electroweak phase transition becomes weak

We measure the interface tension near the phase transition endpoint of the 3d SU(2)-Higgs model. The tunnel correlation length method is used and compared to other approaches. A modified scaling behaviour for the mass gap as function of the transverse area is proposed. (orig.)Available from FIZ Karlsruhe / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

3-dimensional lattice studies of the electroweak phase transition at M_H_i_g_g_s#approx# 70 GeV

We study the electroweak phase transition by lattice simulations of an effective 3-dimensional theory, for a Higgs mass of about 70 GeV. Exploiting, among others, a variant of the equal weight criterion of phase equilibrium, we obtain transition temperature, latent heat and surface tension, and compare with M_H#approx#35 GeV. In the broken phase masses and Higgs condensates are compared to perturbation theory. For the symmetric phase, bound state masses and the static force are determined. (orig.)28 refs.SIGLEAvailable from TIB Hannover: RA 2999(113) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Renormalization of four-fermion operators for higher twist calculations

The evaluation of the higher twist contributions to deep inelastic scattering amplitudes involves a non trivial choice of operator bases for the higher orders of the OPE expansion of the two hadronic currents. In this talk we discuss the perturbative renormalization of the four-fermion operators that appear in the above bases. (orig.)7 refs.Available from TIB Hannover: RA 2999(98-132) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Perturbative renormalization of lattice bilinear quark operators

Our aim is to compute the lower moments of the unpolarized and polarized deep-inelastic structure functions of the nucleon on the lattice. The theoretical basis of the calculation is the operator product expansion. To construct operators with the appropriate continuum behavior out of the bare lattice operators one must absorb the effects of momentum scales far greater than any physical scale into a renormalization of the operators. In this work we compute the renormalization constants of all bilinear quark operators of leading twist and spin up to four. The calculation is done for Wilson fermions and in the quenched approximation where dynamical quark loops are neglected. (orig.)21 refs.Available from TIB Hannover: RA 2999(96-034) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

New results for non-perturbative O(a) improvement in light hadrons

We have results from light hadron simulations in quenched QCD at #beta# 6.0 and 6.2 using non-perturbatively improved Sheikholeslami-Wohlert fermions in an effort to remove all O(a) effects. From looking at hadron masses and splittings and the RG-invariant quark masses (where we have one point at #beta# = 5.7) we suggest this is plausible even with the limited data set. The interpretation of the decay constants appears to be less clear. (orig.)SIGLEAvailable from TIB Hannover: RA 2999(97-198) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Lattice computation of structure functions

Recent lattice calculations of hadron structure functions are described. (orig.)21 refs.Available from TIB Hannover: RA 2999(96-151) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Scaling of non-perturbative O(a) improved Wilson fermions: Hadron spectrum, quark masses and decay constants

We compute the hadron mass spectrum, the quark masses and the meson decay constants in quenched lattice QCD with non-perturbatively O(a) improved Wilson fermions. The calculations are done for two values of the coupling constant, #beta# = 6.0 and 6.2, and the results are compared with the predictions of ordinary Wilson fermions. We find that the improved action reduces lattice artifacts as expected. (orig.)SIGLEAvailable from FIZ Karlsruhe / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Recent results on the nucleon structure functions from lattice QCD

We report on recent results of a high statistics lattice calculation of the unpolarized and polarized structure functions of the nucleon. (orig.)9 refs.Available from TIB Hannover: RA 2999(95-203) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Non-perturbative versus perturbative renormalization of lattice operators

Our objective is to compute the moments of the deep-inelastic structure functions of the nucleon on the lattice. A major source of uncertainty is the renormalization of the lattice operators that enter the calculation. In this talk we compare the renormalization constants of the most relevant twist-two bilinear quark operators which we have computed non-perturbatively and perturbatively to one loop order. Furthermore, we discuss the use of tadpole improved perturbation theory. (orig.)6 refs.SIGLEAvailable from TIB Hannover: RA 2999(95-179) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Renormalisation and off-shell improvement in lattice perturbation theory

We discuss the improvement of flavour non-singlet point and one-link lattice quark operators, which describe the quark currents and the first moment of the DIS structure functions respectively. Suitable bases of improved operators are given, and the corresponding renormalisation factors and improvement coefficients are calculated in one-loop lattice perturbation theory, using the Sheikholeslami-Wohlert (clover) action. To this order we achieve off-shell improvement by eliminating the effect of contact terms. We use massive fermions, and our calculations are done keeping all terms up to first order in the lattice spacing, for arbitrary m"2/p"2, in a general covariant gauge. We also compare clover fermions with fermions satisfying the Ginsparg-Wilson relation, and show how to remove O(a) effects off-shell in this case too, and how this is in many aspects simpler than for clover fermions. Finally, tadpole improvement is also considered. (orig.)SIGLEAvailable from TIB Hannover: RA 2999(00-049) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman