Abstract:
Within the framework of the MSSM, we compute the complete set of electroweak one-loop supersymmetric quantum effects on the width $\Gamma_Z$ of the $Z$-boson in the on-shell renormalization scheme. Numerical analyses of the corrections to the various partial widths into leptons and quarks are presented. On general grounds, the average size of the electroweak SUSY corrections to $\Gamma_Z$ may well saturate the level of the present theoretical uncertainties, even if considering the full supersymmetric spectrum lying in the neighbourhood of the unaccessible LEP 200 range. Remarkably enough, for the present values of the top quark mass, the electroweak SUSY effects could be, globally, very close or even bigger than the electroweak SM corrections, but opposite in sign. Therefore, in the absence of theoretical errors, there are large regions of parameter space where one could find that, effectively, the electroweak SM corrections are ``missing'', or even having the ``wrong'' sign. This should be helpful in discriminating between the SM and the MSSM. However, an accurate prediction of the electroweak quantum effects on $\Gamma_Z$ will only be possible, if $\Delta r$ and $\alpha_s$ are pinned down in the future with enough precision.

Abstract:
Within the framework of the MSSM, we compute the electroweak one-loop supersymmetric quantum corrections to the width $\Gamma (t\rightarrow W^{+}\, b)$ of the canonical main decay of the top quark. The results are presented in two on-shell renormalization schemes parametrized either by $\alpha$ or $G_F$. While in the standard model, and in the Higgs sector of the MSSM, the electroweak radiative corrections in the $G_F$-scheme are rather insensitive to the top quark mass and are of order of $1\%$ at most, the rest (``genuine'' part) of the supersymmetric quantum effects in the MSSM amount to a non-negligible correction that could be about one order of magnitude larger, depending on the top quark mass and of the region of the supersymmetric parameter space. These new electroweak effects, therefore, could be of the same order (and go in the same direction) as the conventional leading QCD corrections.

Abstract:
We discuss the QCD and leading electroweak corrections to the hadronic width of the charged Higgs boson of the MSSM. In our renormalization framework, tan(beta) is defined through Gamma(H^+ -> tau^+ nu_{tau}). We show that a measurement of the hadronic width of H^\pm and/or of the branching ratio of its tau-decay mode with a modest precision of ~20% could be sufficient to unravel the supersymmetric nature of H^\pm in full consistency with the low-energy data from radiative B-meson decays.

Abstract:
We compute the one-loop supersymmetric QCD quantum effects on the width $\Gamma (t\rightarrow W^{+}\, b)$ of the canonical main decay of the top quark within the framework of the MSSM. The corrections can be of either sign depending on whether the stop squark mass is above or below the top quark decay threshold into stop and gluino $\Gamma (t\rightarrow\tilde{t} \,\tilde{g})$. For $m_{\tilde{t}}$ above that threshold, the corrections are negative and can be of the same order (and go in the same direction) as the ordinary QCD corrections, even for stop and gluino masses of ${\cal O}(100)\,GeV$. Since the electroweak supersymmetric quantum effects turn out to be also of the same sign and could be of the same order of magnitude, the total MSSM correction to the top quark width could potentially result in a rather large ${\cal O}(10-25)\%$ reduction of $\Gamma (t\rightarrow W^{+}\, b)$ far beyond the conventional QCD expectations.

Abstract:
We survey all possible supersymmetric three-body decays of the top quark in the framework of the MSSM and present detailed numerical analyses of the most relevant cases. Although the two-body channels are generally dominant, it is not inconceivable that some or all of our most favourite two-body SUSY candidates could be suppressed. In this event there is still the possibility that some of the available three-body SUSY modes might exhibit a substantial branching fraction and/or carry exotic signatures that would facilitate their identification. Furthermore, in view of the projected inclusive measurement of the top-quark width $\Gamma_t$ in future colliders, one should have at one's disposal the full second order correction (electroweak and strong) to the value of that parameter in the MSSM. Our analysis confirms that some supersymmetric three-body decays could be relevant and thus contribute to $\Gamma_t$ at a level comparable to the largest one loop supersymmetric effects on two-body modes recently computed in the literature.

Abstract:
We compute the partial width of the FCNC top quark decay t->c h in the framework of the Minimal Supersymmetric Standard Model, where h = h0, H0, A0 is any of the neutral Higgs of the MSSM. We include the SUSY electroweak, Higgs, and SUSY-QCD contributions. Our results substantially improve previous estimations on the subject, and we find that there is a possibility that they can be measured at LHC.

Abstract:
Observing a heavy charged Higgs boson produced in the near future at the Tevatron or at the LHC would be instant evidence of physics beyond the Standard Model. Whether such a Higgs boson would be supersymmetric or not it could only be decided after accurate prediction of its properties. Here we compute the decay width of the dominant decay of such a boson, namely H^+ -> t \bar{b}, including the leading electroweak corrections originating from large Yukawa couplings within the MSSM. These electroweak effects turn out to be of comparable size to the O(alpha_s) QCD corrections in relevant portions of the MSSM parameter space. Our analysis incorporates the stringent low-energy constraints imposed by radiative B-meson decays.

Abstract:
The Minimal supersymmetric extension of the Standard Model (MSSM) with light stops, charginos or pseudoscalar Higgs bosons has been suggested as an explanation of the too high value of the branching ratio of the Z0 boson into b quarks (Rb anomaly). A program including all radiative corrections to the MSSM at the same level as the radiative corrections to the SM has been developed and used to perform global fits to all electroweak data from LEP, SLC and the Tevatron. The probability of the global fit improves from 8% in the SM to 18% in the MSSM. Including the b->s gamma rate, as measured by CLEO, reduces the probability from 18% to 15%. In the constrained MSSM requiring unification and electroweak symmetry breaking no improvement of Rb is possible.

Abstract:
We argue that the creation of a baryon asymmetry in the early universe is an intriguing case where several aspects of ``Beyond'' physics are needed. We then concentrate on baryogenesis in a strong first-order phase transition and discuss that supersymmetric variants of the electroweak theory (MSSM and some version of NMSSM) rather naturally provide the necessary ingredients. The charginos and the stops play a prominent role. We present CP-violating dispersion relations in the chargino sector and show results of a concrete model calculation for the asymmetry production based on quasi-classical Boltzmann transport equations and sphaleron transitions in the hot electroweak phase.

Abstract:
Contrary to common belief, the requirement that supersymmetry exists and that there are two Higgs doublets and no singlet at the electroweak energy scale does not necessarily result in the minimal supersymmetric standard model (MSSM). Two interesting alternatives are presented.