Giuseppe Degrassi

Towards high-precision predictions for the MSSM Higgs sector

Abstract. 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 mh within the MSSM is shifted upwards. Consequently, lower limits on

Investigating the near-criticality of the Higgs boson

\tan\beta

Two-loop light fermion contribution to Higgs production and decays

obtained by confronting the upper bound as function of

B→Xsγ in supersymmetry: large contributions beyond the leading order

\tan\beta

On the neutral Higgs boson masses in the MSSM for arbitrary stop mixing

with the lower bound on mh from Higgs searches are significantly weakened. Furthermore, th e region in the MA-

Next-to-leading QCD corrections to B → Xsγ in supersymmetry

\tan\beta

On the two-loop sbottom corrections to the neutral Higgs boson masses in the MSSM

-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.

On the two-loop Yukawa corrections to the MSSM Higgs boson masses at large tanβ

A bstractWe 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.

Two-loop electroweak corrections to Higgs production at hadron colliders

We compute the electroweak corrections due to the light fermions to the production cross section σ(gg ! H) and to the partial decay widths ( H ! γ γ) and ( H ! g g). 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 ( H ! gg) the corrections are large in the Higgs mass region below 160 GeV where they reach up to 9% of the lowest order term. For the decay width ( H ! γγ) the corrections for Higgs mass above 160 GeV can reach 10% of the lowest order term.

Higgs production via gluon fusion in the POWHEG approach in the SM and in the MSSM

We discuss possible large contributions to B→Xsγ, which can occur at the next-to-leading order in supersymmetric models. They can originate from terms enhanced by tan β factors, when the ratio between the two Higgs vacuum expectation values is large, or by logarithm of MSUSY/MW, when the supersymmetric particles are considerably heavier than the W boson. We give compact formulae which include all potentially large higher-order contributions. We find that tan β terms at the next-to-leading order do not only appear from the Hall-Rattazzi-Sarid effect (the modified relation between the bottom mass and Yukawa coupling), but also from an analogous effect in the top-quark Yukawa coupling. Finally, we show how next-to-leading order corrections, in the large tan β region, can significantly reduce the limit on the charged-Higgs mass, even if supersymmetric particles are very heavy.