[en] This document is divided into 2 parts. The first part describes a particular re-summation technique of perturbative series that can give a non-perturbative results in some cases. We detail some applications in field theory and in condensed matter like the calculation of the effective temperature of Bose-Einstein condensates. The second part deals with the minimal supersymmetric standard model. We present an accurate calculation of the mass spectrum of supersymmetric particles, a calculation of the relic density of supersymmetric black matter, and the constraints that we can infer from models

[en] Deviations from standard model in parameters measured at LEP and other experiments are discussed, resulting from an additional SU(2)_V boson with specific properties. This new boson may be expected typically as a vector resonance in no-Higgs scenarios (e.g. strongly interacting Higgs sector, or composite W models), but also in more conventional (renormalizable) SU(2)_V extensions of the electroweak theory. It is also argued that the deviations might conspirate to allow a substantially higher top mass than the standard one, due to the peculiar SU(2) global structure and breaking within such model. The possible relevance of these features to some recent models of dynamical electroweak breaking via heavy top condensation is briefly motivated. (author) 21 refs

[en] We analyze the production of neutral Higgs particles in association with the supersymmetric scalar partners of the third generation quarks at future high-energy hadron colliders (upgraded Tevatron, LHC) and e⁺e^- linear machines (including the γγ option). In the Minimal Supersymmetric extension of the Standard Model, the cross section for the associated production of the lightest neutral h boson with the lightest top squark pairs can be rather substantial at high energies. This process would open a window for the measurement of the ht-tildet-tilde coupling, the potentially largest coupling in the supersymmetric theory

[en] We present here an overview of the SuSpect3 project, ultimately aimed to be a major upgrade of the present SuSpect2 code for calculation of spectra in various supersymmetric models. As a benchmark point the well known mSUGRA point SPS1a has been used to compare SuSpect3 and SuSpect2. The first comparisons for SPS1a show a very good agreement

[en] A modification of perturbation theory, known as the delta expansion (variationally improved perturbation), gave rigorously convergent series in some D=1 models (oscillator energy levels) with factorially divergent ordinary perturbative expansions. In a generalization of the variationally improved perturbation technique appropriate to renormalizable asymptotically free theories, we show that the large expansion orders of certain physical quantities are similarly improved, and prove the Borel convergence of the corresponding series for m_v < or∼ 0, with m_v the new (arbitrary) mass perturbation parameter. We argue that non-ambiguous estimates of quantities relevant to dynamical (chiral) symmetry breaking in QCD are possible in this resummation framework. (orig.)

[en] We re-examine a modification of perturbative expansions, valid for asymptotically free theories, producing ''variationally improved'' expansions of physical quantities relevant to dynamical (chiral) symmetry breaking. The large order behaviour of this expansion is shown to be drastically improved, for reasons analogous to the convergence properties of the delta-expansion of the anharmonic oscillator. (author)

[en] We present the implementation of the radiative corrections of the Higgs sector in three public computer codes for the evaluation of the particle spectrum in the Minimal Supersymmetric Standard Model, Softsusy, Spheno and SuSpect. We incorporate the full one-loop corrections to the Higgs boson masses and the electroweak symmetry breaking conditions, as well as the two-loop corrections controlled by the strong gauge coupling and the Yukawa couplings of the third generation fermions. We include also the corrections controlled by the tau Yukawa coupling that we derived for completeness. The computation is consistently performed in the DRbar renormalisation scheme. In a selected number of MSSM scenarios, we study the effect of these corrections and analyse the impact of some higher order effects. By considering the renormalisation scheme and scale dependence, and the effect of the approximation of zero external momentum in the two-loop corrections, we estimate the theoretical uncertainty on the lighter Higgs boson mass to be 3 to 5 GeV. The uncertainty on Mh due to the experimental error in the measurement of the SM input parameters is approximately of the same size. Finally, we discuss the phenomenological consequences, using the latest value of the top quark mass. We find, in particular, that the most conservative upper bound on the lighter Higgs boson mass in the general MSSM is Mh < 152 GeV and that there is no lower bound on the parameter tan(beta) from non-observation of the MSSM Higgs bosons at LEP2. (author)

[en] We compare the effects of non-standard weak bosons (NSB) expected from E₆-Superstrings (Z'), strong Higgs (V₀) and composite (spin 0,1,2) models by using the classical inclusive e^±p → e^± + ''Hadrons'' processes at HERA energies. By assuming a 30% uncertainty for the measurement of the differential cross-sections for unpolarized e^± beams and a deviation |ΔA|=0.1 from the longitudinal asymmetry of the Standard Model (SM), we derive significant bounds on the masses of composite NSB with the exception of the excited Z*. The V₀ of the strong Higgs model is unobservable. Useful bounds on the Z' of the E₆ and the Z* can only be obtained by increasing the precision measurements (|ΔA|≤0.05) of the longitudinal asymmetry. Therefore, we give bounds on these NSB for |ΔA|=0.02 after selecting the combination of longitudinal asymmetries where their effects are optimal. (authro). 14 refs, 7 figs, 5 tabs

[en] The one-loop-corrected helicity amplitudes and the cross section for e⁺e^-→W⁺W^- are represented in terms of invariant amplitudes related to corrections to Born-level gauge couplings as well as magnetic dipole, electric quadrupole, anapole, t-channel-exchange and contact interactions. Neglecting all but the (three) ultraviolet and infrared sensitive corrections to the gauge couplings yields an improved Born approximation which is sufficiently accurate for most practical purposes. (orig.)

[en] We examine an extended electroweak theory based on SU(2)_LxSU(2)_vxU(1)_y and constrained by ρ = 1 at tree level. Various models previously considered in the literature appear as special cases of our framework. The non-decoupling of the additional neutral vector boson V_o for m_v → ∞ is traced back to the extra point-like photon interaction of leptons and quarks contained in the Hung-Sakurai electroweak model based on γW³ mixing. A comparison of the predictions of the present model with precision electroweak data (M sub(Z_O), M_W±, anti s_W²) will allow one to quantify how firmly SU(2)_LxU(1)_y symmetry of vector-boson-fermion interactions is established by these data. (orig.)