[en] Physics at the Large Hadron Collider (LHC) and the International e⁺e^- Linear Collider (ILC)will be complementary in many respects, as has been demonstrated at previous generations of hadron and lepton colliders. This report addresses the possible interplay between the LHC and ILC in testing the Standard Model and in discovering and determining the origin of new physics. Mutual benefits for the physics programme at both machines can occur both at the level of a combined interpretation of Hadron Collider and Linear Collider data and at the level of combined analyses of the data, where results obtained at one machine can directly influence the way analyses are carried out at the other machine. Topics under study comprise the physics of weak and strong electroweak symmetry breaking, supersymmetric models, new gauge theories, models with extra dimensions, and electroweak and QCD precision physics. The status of the work that has been carried out within the LHC/LC Study Group so far is summarized in this report. Possible topics for future studies are outlined

No abstract available

[en] In the Minimal Supersymmetric Standard Model (MSSM) we incorporate the Higgs-boson propagator corrections, evaluated up to two-loop order, into the prediction of the cross sections for the Higgs boson production mechanism, e⁺e^- → hZ, hA, and into the evaluation of Higgs decay rates and branching ratios, Γ(h → ff-bar) and BR(h → ff-bar) for f = b, τ. The propagator corrections consist of the full one-loop contribution, including the effects of non-vanishing external momentum, and at the two-loop level of the dominant corrections of O(αα_s) and further sub-dominant contributions. The results are supplemented with one-loop vertex and box corrections. The effects of the two-loop propagator corrections and of specific one-loop contributions are investigated in detail. Our results are compared with the result obtained within the renormalization group approach. Agreement within O(10%) is found for most parts of the MSSM parameter space

[en] Higher-order results for electroweak precision observables in the Standard Model are analyzed in view of the experimental accuracies achievable at the present and the next generation of colliders, and the indirect prediction of the Higgs-boson mass from the precision data is discussed. Within the MSSM, two-loop results for the lightest CP-even Higgs-boson mass are confronted with the most recent LEP data. Possible precision tests of the MSSM at a future linear collider are furthermore investigated

[en] An interesting feature of the next-to-minimal supersymmetric standard model (NMSSM) is that one or more Higgs bosons may be comparably light (M_Hi< M_Z) without being in conflict with current experimental bounds. Due to a large singlet component, their direct production in standard channels at the Large Hadron Collider (LHC) is suppressed. We demonstrate that there are good prospects for observing such a light Higgs boson in decays of heavy neutralinos and charginos. We consider an example scenario with 20 GeV< M_H1< M_Z and show that a large fraction of the cascade decays of gluinos and squarks involves the production of at least one Higgs boson. Performing a Monte Carlo analysis at the level of fast detector simulation, it is demonstrated how the Higgs signal can be separated from the main backgrounds, giving access to the Yukawa coupling of the Higgs to bottom quarks. Analyzing the resulting b anti b mass spectrum could provide an opportunity for light Higgs boson discovery already with 5 fb^-1 of LHC data at 7 TeV. (orig.)

No abstract available

[en] The Higgs boson search has shifted from LEP2 to the Tevatron and will subsequently move to the LHC. Due to the different initial states, the Higgs production and decay channels relevant for Higgs boson searches were different at LEP2 to what they are at hadron colliders. They suggest new benchmark scenarios for the MSSM Higgs boson search at hadron colliders that exemplify the phenomenology of different parts of the MSSM parameter space. Besides the m_h^max scenario and the no-mixing scenario used in the LEP2 Higgs boson searches, they propose two new scenarios. In one the main production channel at the LHC, gg → h, is suppressed. In the other, important Higgs decay channels at the Tevatron and at the LCH, h → b bar b and h → τ⁺τ^-, are suppressed. All scenarios evade the LEP2 constraints for nearly the whole M_A-tan β-plane

[en] Higher-order contributions to the precision observables Δr, sin² Θ_eff and Γ_l are discussed. The Higgs-mass dependence of the observables is investigated at the two-loop level, and exact results are derived for the Higgs-dependent two-loop corrections associated with fermions. The top-quark corrections are compared with the results obtained by an expansion in the top-quark mass up to next-to-leading order. For the pure fermion-loop contributions to Δr results up to four-loop order are derived. They allow to investigate the validity of the commonly used resummation of the leading fermionic contributions to Δr. (author)

[en] A summary of recent results obtained for higher-order corrections to precision observables in the Standard Model and the Minimal Supersymmetric Standard Model is given. In the Standard Model, electroweak two-loop results valid for arbitrary values of the masses of the top quark, the Higgs boson and the gauge bosons are discussed. For the example of two specific diagrams the exact two-loop result is compared with the result of an expansion in the top-quark mass up to next-to-leading order. Furthermore the Higgs-mass dependence of the two-loop corrections to the relation between the gauge-boson masses is analyzed. In the MSSM, the gluonic corrections to Δr are derived. They are compared with the leading contribution entering via the ρ parameter. (author)

[en] We study the implications of a scalar bottom quark, with a mass of O(5 GeV) , within the minimal supersymmetric standard model. Light sbottoms may naturally appear for large tan β and, depending on the decay modes, may have escaped experimental detection. We show that a light sbottom cannot be ruled out by electroweak precision data and the bound on the lightest CP-even Higgs-boson mass. We infer that a light tilde b scenario requires a relatively light scalar top quark whose mass is typically about the top-quark mass. In this scenario the lightest Higgs boson decays predominantly into tilde b pairs and obeys the mass bound m_h∼<123 GeV