Threshold effects and radiative electroweak symmetry breaking in $SU(5)$ extensions of the MSSM

Abstract

We make a complete analysis of radiative symmetry breaking in the MSSM and its $SU(5)$ extensions including low- and high-energy threshold effects in the framework of the two-loop renormalization group. In particular, we consider minimal $SU(5)$, the ``missing-doublet'' $SU(5)$, a Peccei-Quinn invariant version of $SU(5)$ as well as a version with light adjoint remnants. We derive permitted ranges for the parameters of these models in relation to predicted ${\alpha }_s$ and $M_G$ values within the present experimental accuracy. The parameter regions allowed under the constraints of radiative symmetry breaking, perturbativity and proton stability, include the experimentally designated domain for ${\alpha }_s$. In the case of the minimal $SU(5)$, the values of ${\alpha }_s$ obtained are somewhat large in comparison with the experimental average. The ``missing-doublet'' $SU(5)$, generally, predicts smaller values of ${\alpha }_s$. In both versions of the ``missing-doublet'', the high energy threshold effects on ${\alpha }_s$ operate in the opposite direction than in the case of the minimal model, leading to small values. In the case of the Peccei-Quinn version however the presence of an extra intermediate scale allows to achieve an excellent agreement with the experimental ${\alpha }_s$ values. Finally, the last considered version, with light remnants, exhibits unification of couplings at string scale at the expense however of rather large ${\alpha }_s$ values.

18 pages, LaTeX2e,uses epsf,9 figures,full postscript file available at http://artemis.cc.uoi.gr/~dedes/new96.ps.gz

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• Hybrid Inflation from Supersymmetric SU(5)
• Low Energy Thresholds and the Renormalization Group in the MSSM
• D-term Spectroscopy in Realistic Heterotic-String Models
• The Effective Weak Mixing Angle in the MSSM
• Radiative GUT Symmetry Breaking in a R-Symmetric Flipped SU(5) Model
• Suppressing dimension-5 operators in general SU(5) models
• b-tau Unification and neutrino masses in SU(5) extensions of the MSSM with radiative electroweak symmetry breaking
• Towards a Two-Loop Matching of Gauge Couplings in Grand Unified Theories
• On Nonstandard Vacuua in Minimal Supergravity Models
• Collective treatment of High Energy Thresholds in SUSY - GUTs