We present the results of a complete analysis of the one-loop electroweak corrections to e–e+-->gammagamma, Zgamma, ZZ in the standard model (SM) and the minimal supersymmetric standard model (MSSM). A special emphasis is put on the high energy behavior of the various helicity amplitudes and the way the logarithmic structure is generated. The large magnitude of these effects, which induce striking differences between the SM and MSSM cases at high energies, offers the possibility of making global tests which could check the consistency of these models, and even decide whether any additional new physics is required.

We review the present status for the determinations of the light and heavy quark masses, the light quark chiral condensate and the decay constants of light and heavy-light (pseudo)scalar mesons from QCD spectral sum rules (QSSR). Bounds on the light quark running masses at 2 GeV are found to be: 6 MeV<(m_d+m_u)(2)<11 MeV and 71 MeV/=0.66\pm 0.10. The last section is dedicated to the QSSR determinations of f_{D_{(s)}} and f_{B_{(s)}}.

t is widely believed that dark matter exists within galaxies and clusters of galaxies. Under the assumption that this dark matter is composed of the lightest, stable supersymmetric particle, assumed to be the neutralino, the feasibility of its indirect detection via observations of a diffuse gamma-ray signal due to neutralino annihilations within M31 is examined. To this end, first the dark matter halo of the close spiral galaxy M31 is modeled from observations, then the resultant gamma-ray flux is estimated within supersymmetric model configurations. We conclude that under favorable conditions such as the rapid accretion of neutralinos on the central black hole in M31 and/or the presence of many clumps inside its halo with $r^{-3/2}$ inner profiles, a neutralino annihilation gamma-ray signal is marginally detectable by the ongoing collaboration CELESTE.

The primordial helium abundance Y_p is commonly inferred from abundance determinations in low-metallicity extragalactic HII-regions. Such determinations may be subject to systematic uncertainties that are investigated here. Particular attention is paid to two effects: icf-corrections for ``imperfect'' ionization structure leading to significant amounts of (unobservable) neutral helium or hydrogen and ``tcf''-corrections due to non-uniform temperature. Model HII-regions with a large number of parameters are constructed and it is shown that required corrections are almost exclusively functions of two physical parameters: the number of helium- to hydrogen- ionizing photons in the illuminating continuum Q(He0)/Q(H0), and the ratio of width to radius delta r_S/r_S of the Stromgren sphere. For clouds of sufficient He-ionizing photons Q(He0)/Q(H0) >~ 0.15 and non-negligible width of the Stromgren sphere a significant overestimate of helium abundances may result. Such clouds show radiation softness parameters in the range -0.4 <~ log(eta) <~ 0.3 coincident with the range of eta in observed HII-regions. Existing data of HII-regions indeed seem to display a correlation which is consistent with a typical ~ 2-4% overestimate of helium abundances due to these effects. In case such an interpretation prevails, and in the absence of other compensating effects, a significant downward revision of Y_p may result. It is argued that caution should be exercised regarding the validity of commonly quoted error bars on Y_p.

We point out that the lowest dimension operators that preserve SU(2)×U(1) gauge invariance and induce gauge boson self-interactions affecting only the neutral gauge bosons are just two dim=8 operators. If these operators constitute the only new physics source, there will then exist only two independent anomalous couplings affecting Z and γ: i.e., one CP conserving and one CP violating. On this basis, we give the corresponding relations among the ZZZ, ZZγ, and γγZ couplings used up to now in the analyses of experimental data. A reanalysis taking these relations into account should produce much more stringent constraints on the anomalous couplings.

We consider the production of supersymmetric (SUSY) scalar pairs at lepton colliders, for c.m. energies much larger than the mass of the heaviest SUSY (real or virtual) particle involved in the process. In that energy regime, we derive the leading and subleading terms of the electroweak Sudakov logarithms in the MSSM, first working at one loop with physical states and then resumming to all orders with asymptotic expansions. We show that the first order of the resummed expression reproduces the physical one loop approximation, and compute systematically the possible effects on various observables both at one loop and to all orders. We discuss the regimes and the observables where the one loop approximation can or cannot be trusted, working in an energy range between 1 TeV and 4 TeV under a “light” SUSY mass assumption. As a by-product of our analysis, we propose a determination of the MSSM parameter tan β showing how a relative accuracy ≃25% can be easily achieved in the region tan β≳14, under reasonable experimental assumptions.