We present the first complete next-to-next-to-leading order analysis of the Standard Model Higgs potential. We computed the two-loop QCD and Yukawa corrections to the relation between the Higgs quartic coupling (λ) and the Higgs mass (M h ), reducing the theoretical uncertainty in the determination of the critical value of M h for vacuum stability to 1 GeV. While λ at the Planck scale is remarkably close to zero, absolute stability of the Higgs potential is excluded at 98% C.L. for M h < 126 GeV. Possible consequences of the near vanishing of λ at the Planck scale, including speculations about the role of the Higgs field during inflation, are discussed.

We extract from data the parameters of the Higgs potential, the top Yukawa coupling and the electroweak gauge couplings with full 2-loop NNLO precision, and we extrapolate the SM parameters up to large energies with full 3-loop NNLO RGE precision. Then we study the phase diagram of the Standard Model in terms of high-energy parameters, finding that the measured Higgs mass roughly corresponds to the minimum values of the Higgs quartic and top Yukawa and the maximum value of the gauge couplings allowed by vacuum metastability. We discuss various theoretical interpretations of the near-criticality of the Higgs mass.

The status of the evaluation of the MSSM Higgs sector is reviewed. The phenomenological impact of recently obtained corrections is discussed. In particular it is shown that the upper bound on m h within the MSSM is shifted upwards. Consequently, lower limits on tan β obtained by confronting the upper bound as function of tan β with the lower bound on m h from Higgs searches are significantly weakened. Furthermore, the region in the M A -tan β-plane where the coupling of the lightest Higgs boson to down-type fermions is suppressed is modified. The presently not calculated higher-order corrections to the Higgs-boson mass matrix are estimated to shift the mass of the lightest Higgs boson by up to 3 GeV. *

We compute the QCD next-to-leading order matching conditions of the (chromo)-magnetic operators relevant for B → X s γ in supersymmetric models with minimal flavour violation. The calculation is performed under the assumption that the charginos and one stop are lighter than all other squarks and the gluino. In the parameter region where a light charged Higgs boson is consistent with measurements of BR(B → X s γ), we find sizeable corrections to the Wilson coefficients. As a consequence, there is a significant reduction of the stop-chargino mass region where the supersymmetric contribution has a large destructive interference with the charged-Higgs boson contribution. * On leave of absence from INFN, Sez. di Padova, Italy.

No abstract

We compute the O(alpha (l)alpha (s)) two-loop corrections to the neutral Higgs boson masses in the Minimal Supersymmetric extension of the Standard Model. An appropriate use of the effective potential allows us to obtain simple analytical formulae, valid for arbitrary values of m(A) and of the mass parameters in the stop sector. We elucidate some subtleties of the effective potential calculation, and find full agreement with the numerical output of the existing diagrammatic calculation. We discuss in detail the limit of heavy gluino. (C) 2001 Elsevier Science B.V. All rights reserved

We compute the electroweak corrections due to the light fermions to the production cross section sigma(gg --> H) and to the partial decay widths Gamma(H --> gammagamma) and Gamma(H --> gg). We present analytic results for these corrections that are expressed in terms of Generalized Harmonic Polylogarithms. We find that for the gluon fusion production cross section and for the decay width Gamma(H --> gg) the corrections are large in the Higgs mass region below 160 GeV, where they grow from 4 to 9% of the lowest order term, while above 160 GeV they are small. For the decay width Gamma(H --> gammagamma) the corrections for Higgs mass above 160 GeV are typically below -5% of the lowest order term but they may reach O(-10%) for m(H) similar to 2m(W). (C) 2004 Elsevier B.V. All rights reserved

We present the QCD corrections to the matching conditions of the ∆B = 1 magnetic and chromo-magnetic operators in the Standard Model and in two-Higgs doublet models. We use an off-shell matching procedure which allows us to perform the computation using Taylor series in the external momenta, instead of asymptotic expansions. In the Standard Model case, we confirm previous results derived onshell and we obtain BR(B → X s γ) = (3.62 ± 0.33) × 10 −4 . In the case of the usual two-Higgs doublet model, we show that going from the leading to the nextto-leading order result improves the CLEO bound on the charged-Higgs mass from 260 GeV to 380 GeV. This limit is very sensitive to the definition of errors and we carefully discuss the theoretical uncertainties. Finally, in the case of the two-Higgs doublet model in which both up-and down-type quarks couple to the same Higgs field, the theoretical prediction for BR(B → X s γ) can be reduced by at most 20% with respect to the Standard Model value.