arXiv subjects
Publications and source records attributed to A. Schiller.
The 3d SU(2)-Higgs model is used to find the critical Higgs mass above which the first order phase transition ends. One method is focused on the disappearance of the two-state signal of the scalar condensate (vanishing of the latent heat). Another method is based on the analysis of Lee-Yang zeroes of the partition function which allows to characterise the change from first order transition into an analytical crossover.
We perform a Monte Carlo calculation of the second moment of the polarised valence quark distributions in the nucleon, using quenched Wilson fermions. The special feature of this moment is that it is directly accessible experimentally. At a scale of $μ\approx 2$GeV we find $Δ^{(1)}u = 0.198(8)$, $Δ^{(1)}d = -0.0477(33)$. We compare these numbers with recent experimental results of the SMC collaboration.
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, $β= 6.0$ 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.
We review the status of lattice calculations of the deep-inelastic structure functions of the nucleon. In addition, we present some results on the pion and rho structure functions.
We give a more precise characterisation of the end of the electroweak phase transition in the framework of the effective 3d SU(2)--Higgs lattice model than has been given before. The model has now been simulated at gauge couplings beta_G=12 and 16 for Higgs masses M_H^*=70, 74, 76 and 80 GeV up to lattices 96^3 and the data have been used for reweighting. The breakdown of finite volume scaling of the Lee-Yang zeroes indicates the change from a first order transition to a crossover at lambda_3/g_3^2=0.102(2) in rough agreement with results of Karsch et al (hep-lat/9608087) at β_G=9 and smaller lattices. The infinite volume extrapolation of the discontinuity Delta < phi^+ phi > /g_3^2 turns out to be zero at lambda_3/g_3^2=0.107(2) being an upper limit. We comment on the limitations of the second method.
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.
We calculate the lower moments of the deep-inelastic structure functions of the pion and the rho meson on the lattice. Of particular interest to us are the spin-dependent structure functions of the rho. The calculations are done with Wilson fermions and for three values of the quark mass, so that we can perform an extrapolation to the chiral limit.
We report on measurements of the h_1 structure function, relevant to calculating cross-sections for the Drell-Yan process. This is a quantity which can not be measured in Deep Inelastic Scattering, it gives additional information on the spin carried by the valence quarks, as well as insights on how relativistic the quarks are.
We compute the light hadron mass spectrum in quenched lattice QCD at $β= 6.0$ using the Sheikholeslami-Wohlert fermionic action. The calculation is done for several choices of the coefficient $c_{SW}$, including $c_{SW} = 0$ and the recently proposed optimal value $c_{SW} = 1.769$. We find that the individual masses change by up to 30\% under $O(a)$ improvement. The spectrum calculation suggests $c_{SW} \approx 1.4$ for the optimal value of the coefficient.
We present initial results for light hadron masses and nucleon structure functions using a recent proposal for eliminating all $O(a)$ effects from Wilson fermion simulations in the quenched approximation. With initially limited statistics, we find a much more linear APE plot and a value of the axial coupling $g_A$ nearer to the experimental point than with comparable runs using unimproved Wilson fermions.
Recent lattice calculations of hadron structure functions are described.
The renormalisation constants for local bilinear quark operators are calculated using the Sheikholeslami-Wohlert improved action. In addition we compute the renormalisation constant of the leading gluon operator for different group representations and discuss the mixing of the operators E^2 and B^2.
About half the mass of a hadron is given from gluonic contributions. In this talk we calculate the chromo-electric and chromo-magnetic components of the nucleon mass. These computations are numerically difficult due to gluon field ultra-violet fluctuations. Nevertheless a high statistics feasibility run using quenched Wilson fermions seems to show reasonable signals.
Physical parameters of the electroweak phase transition in a 3d effective lattice SU(2)-Higgs model are presented. The phase transition temperatures, latent heats and continuum condensate discontinuities are measured at Higgs masses of about 70 and 35 GeV. Masses and Higgs condensates are compared to perturbation theory in the broken phase. In the symmetric phase bound states and the static force are determined.
We study the electroweak phase transition in an effective 3-dimensional theory for a Higgs mass of about 70 GeV by Monte Carlo simulations. The transition temperature and jumps of order parameters are obtained and extrapolated to the continuum using multi-histogram techniques and finite size analysis.
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.
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.
For lattice operators that are relevant to the calculation of moments of nucleon structure functions we investigate the transformation properties under the hypercubic group. We give explicit bases of irreducible subspaces for tensors of rank up to 4.