A realistic approach to the standardZ peak

The use of four gauge invariant form factors allows a dense notation of electroweak one loop effects in muon pair production frome ⁺ e ^?-annihilation. These form factors may be interpreted as finite renormalizations of the muon decay constant and of the weak mixing angle. Such a formulation is well adopted for use in Monte Carlo programs. The general formulae are applied to a realistic line shape scan of theZ boson resonance. For a precise determination of theZ boson's mass and width it is sufficient to take data in the small energy region within \(\sqrt s = M_z \pm \Gamma _z /2\) . Finally, it is demonstrated that a simple model independent ansatz yields nearly equally good results.     

Mean field calculations and defect gases in lattice gauge theory

We investigate the relationship between local defects and the mean field method in lattice gauge theory. In particular we clarify the role of defects in establishing the equivalence between mean field calculations with and without gauge fixing. In two dimensions we derive the area law for the Wilson loop by a mean field calculation incorporating defects. We also establish a general rule about mean field variables which are appropriate to handle defects induced by an action that almost possesses a local symmetry group, and we apply it to theZ(2) Higgs model and to the mixedSU(2)-SO(3) model.     

Study of doubly evens d-shell nuclei in the Multi-Configuration-Hartree-Fock model

A theory in the spirit of the Hartree-Fock (HF) model is formulated which takes into account general types of correlation effects. This theory, dubbed as Multi-Configuration Hartree-Fock (MCHF) model, makes use of a multideterminantal trial wave function. In the present work the intrinsic ground state wave functions obtained in this theory have been studied. Doubly evenN=Z andN=Z + 2 nuclei in thesd-shell have been treated and the results have been compared against the HF-predictions. While the HF-approximation is found to be quite good forN=Z nuclei, correlations are found to play a strikingly significant role in theN=Z +2 nuclei.     

Model independent fitting to theZ line shape

An improved model independent formula to fit theZ line shape parameters is presented. The accuracy of the QED radiative corrections used in the formula is estimated, as is the absolute accuracy of the formula itself. The precision of the formula is compared with existing fitting formulae, in terms of cross sections produced and in terms of theZ parameters returned from a fit. The errors which the LEP-SLC experiments can expect to achieve on theZ parameters are examined as a function of total integrated luminosity. The formula presented here can fit theZ parameters with high accuracy: below 1 MeV for theZ mass, the order of 1 MeV for total width, and below 0.04% for the hadronic and leptonic peak cross sections. Such biases will remain much below the expected experimental uncertainties from LEP and SLC.     

The anomalous 3-boson couplings as an implication of the Higgs sector

We discuss the possible new electroweak interactions which may be generated by the Higgs sector at the scale of theZ mass. For this purpose, we give a set ofSU(2)×U(1) gauge invariant operators constructed in terms ofW, Z, γ and Higgs fields which in the unitary gauge describe all possible γWW andZWW anomalous couplings. The dimension of these operators varies from 6 to 12. This fact allows us to consider various scenaria for the manifestations of the New Physics. We conclude that the underlying dynamics induced by the Higgs sector can be tested through a model-independent amplitude analysis of gauge boson pair production at LEP2 and future colliders.     

Flavour dynamics with general scalar fields

We consider a spontaneously broken gauge theory based on the standard model (SM) group with scalar fields that carry arbitrary representations of G, and we investigate some general properties of the charged and neutral current involving these fields. In particular we derive the conditions for having real or complex couplings of the Z boson to two different neutral or charged scalar fields, and for the existence of CP-violating Z-scalar-scalar couplings. Moreover, we study models with the same fermion content as in the SM, with one SU(2) Higgs singlet, and an arbitrary number of Higgs doublets. We show that the structure of the Z-Higgs boson and of the Yukawa couplings in these models can be such that CP-violating form factors which conserve chirality are induced at the one-loop level. Received: 18 December 1998 / Published online: 22 March 1999     

A study of meson-baryon couplings in the constituent quark model

Within the framework of the constituent quark model we discuss the effects of different types of meson-baryon-baryon vertex operators on the form factors and the coupling strengths of the lowest-lying positive and negative parity non-strange baryons. We compare the quark pair creation model (³P₀-model) with the SU(6)-model in which mesons are treated as elementary fields that directly couple to the quarks. The latter model is employed both in the so-called static limit and in a modification motivated by Galilei invariance. It is demonstrated that the inclusion of non-static effects simulates some features of the³P₀ vertex. Especially the reaction πN→ππN is found to be very sensitive to the different assumptions on the dynamics of theq¯q pair creation process. More indirect hints for the internal structure of the mesons might be obtained from the predicted asymmetry for the two form factors ofN→Δ+π andΔ→N+π, which occurs in the³P₀-model, only.     

General analysis ofn-loop corrections in the 2PPI variational approach to λφ4

We present the general analysis of then-loop contribution in a new variational approach to quantum field theory, applied to the scalar model λφ⁴, which is based on the use of an effective action for the local composite operator \(\hat \phi ^2 \) . In a previous paper [1] the three-loop analysis was performed and it was found that the differences with the one loop calculation were very small. We have now generalised this argument for any arbitrary but finite loop calculation. In particular, we examine stability of the precarious phase.     

Production of neutrinos at HERA

For theep collider at HERA, we study processes with neutrinos in the final state. Furthermore, we discuss the production ofW andZ bosons. Because of the very small lifetimes of theW andZ, we consider the production of their leptonic decay products rather than the bosons themselves. All the results are based on exact calculations of the matrix element at the tree level. Total cross sections and various kinematical distributions are presented.     

TheO(ɛ2) scaling law fordσ/dt in the Reggeon Field Theory

We calculate the two loop contributions within the ε-expansion to the Reggeon Field Theory scaling law fordσ/dt, derived using the renormalization group and a general renormalization point for the Pomeron propagator. This generalizes theO(ε) work of Abarbanel, Bartels, Bronzan, and Sidhu. The invariance of the results under certain coupling constant rescalings is demonstrated. We also make some qualitative comments regarding phenomenological applications. Our amplitude in a certain limit approximates the form of the low energy diffractive amplitude advocated by Kane.     

P-odd effectiveZγγγ interactions

A general analysis of the lowest-dimensionalP-oddZγγγ interaction is performed. It turns out that there are only two independent gauge invariant dimension-eight effective Lagrangians of such a type, similarly to theP-even case discussed earlier. It is shown, that such an effective interaction is naturally induced, at the twoloop level, within an extension of the standard model of electroweak interactions involving two-doubletCP-violating Higgs sector.     

Inner-shell ionization by relativistic electron impact

K-, L andM-shell ionization cross sections have been measured for 23 elements, 12≦Z≦92, after bombardment with relativistic electrons, 15≦E ₀65MeV, by means of high resolution semiconductor detectors and a recently developed gas-scintillation proportional counter. For constant electron bombarding energyE ₀ the ionization cross sections follow a power law dependence,σ∽Z ^?α, and forE ₀=50MeV we deducedα =2.45±0.02 for theK shell andα=3.00 ±0.09 for theL shell. The observedZ dependence exhibits significant systematic deviations from theoretical predictions which exceed the experimental values up to 15 % at lowZ elements for theK shell and on the average about 11% for theL andM shell. The same behaviour of too low experimental values, i.e. an overestimation by the theory, is observed for the energy dependence of the cross sections for all shells. A scaling behaviour describing theZ andE ₀ dependence for allK-, L andM-shell data points is observed which also predicts the experimental values by other groups at lower and higher energies correctly. The comparsion of the measuredLΒ/Lα, andLγ/Lα intensity ratios for highZ elements with the values obtained by other groups in the energy range 0.3≦E₀≦1,000 MeV exhibits an increase with bombarding energy that cannot merely be explained by the energy dependence of the subshellionization cross sections for theL shell. An attempt to explain this effect with the change of the Coster-Kronig transition probability is described.     

An effective theory of a compositeZ

It is shown that the experimental value of sin² θ_w can be obtained if theZ is a bound state of two haplons provided that the haplons carry a new hypercolour quantum number in addition to colour. This approach also leads to the prediction that the electromagnetic couplings of theZ are substantially larger than they are in standard electroweak theory. It may be possible to observe these anomalous couplings in the processe ⁺ e ^? →Zγ at LEP 200 where theZ is longitudinally polarised.     

Composite weak bosons in neutrino-lepton scattering

We study effects due to a compositeW or/andZ boson in four different leptonic processes where deviations from the standard model (SM) of electroweak unification may be observed. Compositeness is considered through a simple modification of theW andZ gaugeboson propagator, by a form factor depending on a composition scale parameter. We found that all the four processes point out that this type of propagator modification gives an indication of compositeness if Λ≦400 GeV. For Λ>400 GeV, deviation from SM is negligible.     

Intermediate mass fragments in the reaction6Li+46Ti atE/A=26 MeV

Intermediate mass fragment cross-sectionsσ(E, θ, 4≤Z≤11) have been measured in the reaction⁶Li+⁴⁶Ti at 156 MeV incident energy. A simple sequential binary decay model describes most of theZ>8 data as evaporation from the compound nucleus. The complete fusion cross-section is also well reproduced. An intermediate velocity source model (β=2β _CN, T=7 MeV) has been used in order to explain the small angle and Z≤8 data which indicate aZ ^?4.1 dependence.     

Two-loop electroweak parameters

A recent calculation of the electroweak parameter Δr, including the dominant two-loop contributions and resummation of large logarithms, is reformulated in terms of the dressed gauge-boson propagators and extended to the electroweak quantities measured at theZ peak such as the various partial widths and asymmetries. The formalism is simpler and physically more transparent. Large two-loop corrections specific to theZ→bb \(\bar b\) partial width are included consistently. A detailed statistical analysis is presented of the implications for the topquark and Higgs-boson masses from the latest precision measurements of theW-boson mass and theZ-boson partial widths.     

Quark deconfinement at high temperature and thick vortices

First we describe Mack's effectiveZ(2) theory of quark confinement in theSU(2) lattice gauge theory at zero temperature. Then we show how quarks get liberated above a critical temperature, which has a numerical value somewhat below the glueball mass (in natural units).     

SU(2)L×SU(2)R×U(1) gauge model

We determine here the most general electroweak interaction based on the groupSU(2)_L×SU(2)_R×U(1). When we rotate theZ ₁,Z ₂ basis to theZ,D basis such that the total interaction ofZ with the right-handed current is zero, we obtain an interaction that is free of triangle anomalies. This condition enables us to know the angle through whichZ ₁,Z ₂ basis is to be rotated. We show that the triangle anomaly free interaction obtained by others is contained here as a special case. We also determine the triangle anomaly free weak interaction whenever the neutral (Z,D) bosons are mass eigenstates and show that it reduces to the neutral sector of the standard model whenever g _R ² goes to infinity. The charged sector is also developed here. The most general elements of the masssquared matrix of theZ,D bosons are evaluated. The masses of the left- and right-handed charged bosons are also determined.     

Signatures of thes-leptons andW,Z spins in polarized γe collisions

We study the gaugino +s-electron,Wv andZe photoproductions off electrons with both beams polarized. We make a systematic calculation of the spin and angular asymmetries and obtain model independent results, which allow to identify the spin and/or charge of the scalars-leptons and of the electroweak gauge bosons, either in the high energy limit or at the threshold. For example, the photon helicity asymmetries of theW andZ total cross sections have the distinct value 1 at threshold, but it is negative for the reactions γe→spinor + scalar. In the high energy limit, the same asymmetry for the differential cross sections is equal to one for spin zero boson and negative forW andZ photoproductions and Compton scattering.     

The hadronic contribution to theW andZ mass

In the framework of the standard model of weak interactions, we discuss the hadronic contribution in the radiative correction to the masses of theW andZ boson. Predictions including the nonhadronic parts are given.