Higher-order results for electroweak precision observables in the Standard Model are analyzed in view of the experimental accuracies achievable at the present and the next generation of colliders, and the indirect prediction of the Higgs-boson mass from the precision data is discussed. Within the MSSM, two-loop results for the lightest CP-even Higgs-boson mass are confronted with the exclusion ...

We calculate a two-loop effective potential to the order of O(λtαs) in the MSSM. We then study the corresponding two-loop corrections to the CP -even Higgs-boson mass for arbitrary tanβ and left-right top-squark mixings. We find that the lightest Higgs-boson mass is changed by at most a few GeV. We also show the improved scale dependence and compare to previous two-loop analyses. rjzhang@pheno....

Starting with the two-loop effective potential of the MSSM, and assuming a supersymmetric scale well above MZ , we derive a simple analytical approximation for the lightest CP-even Higgs boson mass including resummation of higher order logarithmic terms via RG-improvement and finite non-logarithmic terms up to O(αsαt). This formula describes the most relevant radiative corrections to the MSSM H...

Abstract A new precision measurement of the W boson mass has been announced by CDF collaboration, which strongly deviates from Standard Model prediction. In this article, we study implications on parameter space $$SU(2)_L$$ S U ( 2 )</mml:mo...

A model of a light Z ′ boson based on gauged L µ − L τ U (1) symmetry is constructed. The Z ′ boson mass is constrained to be in the range of 0.8 to 1 GeV from Z and Z ′ mass relation, g-2 of muon, and tau decays. The two body decay τ → µZ ′ is possible. This will provide a striking signature to test the model.

Small neutrino masses can arise in some grand unified models or superstring theories. We consider a model with an enhanced fermion sector containing Dirac neutral heavy leptons. The dependence on the mass and mixing parameters of these new fermions is investigated for several measurable quantities. We study the flavor-conserving leptonic decays of the Z boson and universal-ity breaking in these...