Electroweak Gauge Theories and Alternative Theories at a Future Linear e+e- Collider

The measurement of Standard Model processes tests the validity of the model at a given scale and is simultaneously sensitive to new physics through loop effects or interference with the Standard Model amplitudes. A variety of studies has been done to see what a linear collider in the energy range MZ < sqrt{s} < 1 TeV can offer. The work that has been done within the ECFA/DESY workshop on linear colliders is reviewed, especially what was not included in the TESLA TDR.Comment: Invited talk presented at the Linear Collider Workshop, Amsterdam, April 200

The physics goals of the TESLA project

As next generation e+e- linear collider the superconducting accelerator project TESLA has been proposed. In this note the physics potential goals of this project, which is highly complementary to LHC, are described.Comment: Invited talk presented at the ``Seventh Topical Seminar on The legacy of LEP and SLC'', Siena, October 200

Experimental studies of Strong Electroweak Symmetry Breaking in gauge boson scattering and three gauge boson production

If no light Higgs boson exist, the interaction among the gauge bosons becomes strong at high energies (~1TeV). The effects of strong electroweak symmetry breaking (SEWSB) could manifest themselves as anomalous couplings before they give rise to new physical states, thus measurement of all couplings and their possible deviation from Standard Model (SM) values could give valuable information for understanding the true nature of symmetry breaking sector. Here we present a detailed study of the measurement of quartic gauge couplings in weak boson scattering processes and a possibility for same measurement in triple weak boson production. Expected limits on the parameters alpha_4 alpha_5,alpha_6, alpha_7 and alpha_10 in electroweak chiral Lagrangian are given.Comment: talk presented at LCWS05, Stanford, USA, March 200

"Pair production of scalar top quarks in e+e- collisions at ILC."

We study the pair production of scalar top quarks in e+e- collisions with the subsequent decay of the top squarks into b-quarks and charginos. We simulate this process using PYTHIA6.4 for beam energies 2E_beam = 350, 400, 500, 800, 1000 GeV. Proposing a set of criteria we obtain a good separation of the signal stop events from top quark pair production which is the main background. The number of stop production events obtained with the proposed cuts for different energies is calculated for an integrated luminosity of 1000 1/fb. We propose a method to reconstruct the mass of the top squark, provided the mass of the lightest neutralino is known, and estimate the error of the mass determination for the case sqrt{s} = 500 GeV.Comment: 25 pages, 27 figures, ILC-NOTE-2008-042. v1 was presented by the 4-th author and published in the Proceedings of the 15-th International Seminar on High Energy Physics QUARKS-2008 (Institute for Nuclear Research of RAS, Sergiev Posad, Russia, 23-29 May 2008), V1, p.227-246, ISBN 978-5-94274-123-5. v2 - another set of cuts was chosen. v3 - some typos correcte

Measuring the Luminosity of a gamma gamma Collider with gamma gamma -> l+ l- gamma Events

The process gamma gamma -> l+ l- is highly suppressed when the total angular momentum of the two colliding photons is zero so that it cannot be used for luminosity determination. This configuration, however is needed for Higgs production at a photon collider. It will be shown that the process gamma gamma -> l+ l- gamma can be used in this case to measure the luminosity of a collider with a precision that is good enough not to limit the error on the partial decay width Gamma(H -> gamma gamma).Comment: Final version, accepted by journa

Measurement of Trilinear Gauge Couplings at a gamma-gamma and e-gamma Collider

The processes gamma gamma -> WW and e gamma -> nu W are sensitive to triple gauge boson interactions. Both reactions have been simulated for hadronically decaying W-bosons and the sensitivity to anomalous couplings has been estimated.Comment: Talk presented at LCWS2002, August 2002, Jeju Island, Kore

The global electroweak fit at NNLO and prospects for the LHC and ILC

For a long time, global fits of the electroweak sector of the Standard Model (SM) have been used to exploit measurements of electroweak precision observables at lepton colliders (LEP, SLC), together with measurements at hadron colliders (Tevatron, LHC), and accurate theoretical predictions at multi-loop level, to constrain free parameters of the SM, such as the Higgs and top masses. Today, all fundamental SM parameters entering these fits are experimentally determined, including information on the Higgs couplings, and the global fits are used as powerful tools to assess the validity of the theory and to constrain scenarios for new physics. Future measurements at the Large Hadron Collider (LHC) and the International Linear Collider (ILC) promise to improve the experimental precision of key observables used in the fits. This paper presents updated electroweak fit results using newest NNLO theoretical predictions, and prospects for the LHC and ILC. The impact of experimental and theoretical uncertainties is analysed in detail. We compare constraints from the electroweak fit on the Higgs couplings with direct LHC measurements, and examine present and future prospects of these constraints using a model with modified couplings of the Higgs boson to fermions and bosons.Comment: 26 pages, 9 figure