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The physics potential of e + e - linear colliders is summarized in this report. These machines are planned to operate in the first phase at a center-of-mass energy of 500 GeV, before being scaled up to about 1 TeV. In the second phase of the operation, a fin
In e+ef- → W+Wf- → q1q2q3q4 events at LEP 2, the two W decay vertices are much closer to each other than typical hadronization distances. Therefore the Bose-Einstein effects, associated with the production of identical bosons (mainly pions), may provide a 'cross-talk' between the W+ and the Wf- decay products. If so, the observable W masses are likely to be affected. We develop algorithms for the
We discuss the possibility of colour rearrangement in {Mathematical expression} events, i.e that the original colour singlets {Mathematical expression} and {Mathematical expression} may be transmuted, for instance, into new singlets {Mathematical expression} and {Mathematical expression}. The effects on event properties could be quite large if such a rearrangement would occur instantaneously, so t
Pythia and JETSET are the two main components of the "Lund Monte Carlo" program suite. They can be used to generate high-energy-physics "events", i.e. sets of outgoing particles produced in the interactions between two incoming particles. Ideally these events should have the same average behaviour and the same fluctuations as real data. The underlying physics is not understood well enough to give
In the hadronic decay mode of a pair of W bosons, e+e-→W+W-→q1q̄2q3qbar4, QCD interference effects can mix up the two color singlets q1q̄2 and q3q̄4, i.e., produce hadrons that cannot be uniquely assigned to either of W+ and W-. We show that interference is negligible for energetic perturbative gluon emission, and develop models to help us to estimate the nonperturbative effects. The total contrib
In events of the type e+e- → tt → bW+bW-, particle production could depend in a non-trivial way on the kinematics of the process. Energetic perturbative gluon radiation can be generated (when kinematically allowed) by the original tt system and by the t → bW+ and t → bW- decays, with negligible interference between the production and decay between the t and t decays. Soft perturbative gluon emissi
A model for high-energy hadronic cross sections is proposed. It is based on Regge theory and perturbative QCD, and includes soft and hard mechanisms as well as diffractive processes. The validity range of Regge-pole theory in the description of total, elastic, single-, and double-diffractive cross sections is investigated and inconsistencies found already at CERN LHC and/or SSC energies. Examining
A real photon has a dual nature, as a pointlike elementary particle and as a qq fluctuation, in the latter case often with hadron-like properties. Therefore high-energy γp interactions have a rich and not yet well explored structure. In this paper, we propose a consistent formulation, which is based on a subdivision of the total cross section into three distinct event classes: direct, VMD and anom
We propose a consistent formulation of high-energy γp interactions, in which these are built up as a sum of three contributions. A significant role is played by the hadronic structure of the photon. From the total cross section at low energy we determine the relative sizes of the hadronic contribution and of the components that make a photon distinctly different from a vector-meson, i.e. direct an
The possibility to discriminate different Higgs production mechanisms using a rapidity gap signature is discussed. The results of Monte Carlo calculations are presented, which show that the two processes WW→H and gg→H indeed have different event structures, but also that these differences, without special care, would be masked by other effects.
If the top is heavy, as now seems likely, the {Mathematical expression} threshold behaviour is given by perturbative QCD. The QCD threshold interaction can be formulated in terms of a potential, attractive or repulsive depending on whether the {Mathematical expression} is in a colour singlet or octet state. This gives a suppression factor for octet production. Singlet production is enhanced, both
Recent progress on the parton distribution functions of the photon, both real and virtual, is briefly reviewed and experimental possibilities at HERA are discussed.
Perturbative QCD corrections to leptoproduction events can be introduced either in the form of matrix elements or of parton showers. Each of these approaches has its advantages and disadvantages, making a comparison of the two interesting. At present energies, both methods can be made to agree reasonably well with data, whereas differences appear at higher energies. The influence of these QCD effe
A number of interrelated topics on jet properties in e+e- annihilation is discussed. The need for different αs values in different fragmentation models is explained, with particular emphasis on the sensitivity to the choice of momentum conservation scheme in independent fragmentation models. Also other factors leading to a broad range of experimental αs values are discussed. Old and new methods to
In perturbative QCD matrix elements, the invariant mass of parton pairs is normally peaked at low values, due to the singularities of the q → qg and g →gg subprocesses. Whereas pairs at large invariant masses give rise to separately visible jets, one may expect a continuous merging back into one single jet, q or g, when the qg or gg invariant mass becomes small. Within the framework of string frag
We study the fragmentation of arbitrary parton configurations, with particular emphasis on events where two partons have a small invariant mass. Within the framework of string fragmentation, a natural transition is obtained between two nearby partons (qg or gg) and a single parton (q or g) carrying the full momentum (provided that colours match), i.e. the final state hadrons are distributed in the
We present a detailed model for exclusive properties of initial state parton showers. A numerically efficient algorithm is obtained by tracing the parton showers backwards, i.e. start with the hard scattering partons and then successively reconstruct preceding branchings in falling sequence of spacelike virtualities Q2 and rising sequence of parton energies. We show how the Altarelli-Parisi equati
After the 2008/2009 global financial crisis, significant policy and scientific attention has been given to ‘green growth’, which aims at the concurrent achievement of economic growth and GHG emissions reductions via de-coupling. Despite ambitious aims, there is a lack of empirical knowledge about the effects and the potential of green growth climate mitigation policies.This thesis aims at providin
