K. Fabricius

Heat bath method for the twisted Eguchi-Kawai model

Abstract We reformulate the twisted Eguchi-Kawai model in a way that allows us to use the heat bath method for the updating procedure of the link matrices. This new formulations is more effecient by a factor of 2.5 in computer time and of 2.3 in memory need.

Numerical checks of the lattice definition independence of topological charge fluctuations

Abstract The stability of our previous results on the topological charge fluctuation in SU(2) is checked against some variations of its lattice definition. The method consists of subtracting a partly computed perturbative tail to Monte Carlo data, whose high statistics are achieved by use of the icosahedral subgroup of SU(2).

Order α2S correction to jet cross sections in e+e− annihilation

We calculate the Sterman-Weinberg type cross section for three jets and the O(α 2 S> ) correction to the thrust distribution σ −1 dσ/d T . The effect on σ −1 dσ/d T is sizeable (in the ¯MS scheme) but not in conflict with the expected convergence of the perturbation series.

Numerical analysis of the twisted Eguchi-Kawai model in four dimensions

Abstract Using Monte Carlo methods we compare the twisted Eguchi-Kawai model for several N values with the SU(∞) lattice gauge theory in two dimensions. We find agreement only for loops with smaller then N2. So the twisted Eguchi-Kawai model does not reproduce the SU(∞) lattice gauge theory on a N2 lattice.

Monte Carlo measurement of the topological susceptibility in SU (3) lattice gauge theory

Abstract A Monte Carlo measurement of the topological susceptibility A=∫ d4x where Q(x) is the topological charge density, is performed in the SU (3) case on a 44 lattice. We find in string tension units A 1 4 =(0.12 ± 0.02) √K as in the SU (2) case. For √K=420 MeV this corresponds to A 1 4 =(50 ± 10) MeV .

A Null Result in Massless {QCD}: Beam - Event Asymmetry in

Abstract The imaginary part of the amplitude e + e − → q q in is calculated the one-loop approximation. It is found to be directly proportional to the Born term contribution. This leads to the vanishing of the beam-event asymmetry in e + e − → q q g width longitudinally polarized beams contrary to the result in e + e − → 1 −− → ggg.

e^+ e^- \to q \bar{q}

Abstract We consider the decay of neutral fireballs with mass M into π +,−,o and derive the first two leading terms of the average multiplicities as a function of M . We discuss the implication of this result for a statistical bootstrap description of e + e − annihilation into hadrons.

G With Longitudinally Polarized Beams

Abstract We introduce classes of twisted reduced models which have identical planar sectors. By taking suitable combinations the planar sector can be extracted. We check the models by Monte Carlo calculations for the two-dimensional twisted Eguchi-Kawai model.

The neutral pion yield in the statistical model for e+e− annihilation

We have determined the shift in Hagedorn temperature due to Bose statistics and calculated explicitly the cluster expansions of fireball level densities. This enabled us to investigate Bose effects in one-particle spectra and integrated correlations. Apart from the low secondary energy region of the one-particle distributions, the nonasymptotic behaviour of these quantities is little affected.

Generalized twisted Eguchi-Kawai models

SummaryThe level density and the decay of isoscalar and isovector fireballs (with input pions) are studied in the framework of the statistical bootstrap model. We find that different versions of this model lead to the same total multiplicity distribution for large fireball massM. Asymptotic expressions for the integrated multiplicity correlation of charged particles are derived. The correlations are calculated numerically in the range 1 GeV⩽M⩽8 GeV.RiassuntoServendosi del modello statistico a bootstrap si studiano la densità dei livelli e il decadimento di fireball isoscalari e isovettoriali (con pioni di entrata). Si trova che per valori elevati della massaM dei fireball versioni diverse di questo modello danno la stessa distribuzione totale di molteplicità. Si deducono espressioni asintotiche per la correlazione di molteplicità integrata delle particelle cariche. Nell’intervallo 1 GeV⩽M⩽⩽8 GeV si calcolano numericamente le correlazioni.РеэюмеВ рамках статистической модели бутстрапа исследуются плотность уровней и распад иэоскалярных и иэовекторных файрболов. Мы получаем, что раэличные варианты зтой модели приводят к одинаковому полному распределению множественности для больщих масс файрболов М. Выводятся асимптотические выражения для корреляции интегральной множественности эаряженных частиц. В области 1 ГзВ⩽M⩽8 ГзВ численно вычисляются укаэанные корреляции.