Abstract
In the MSSM extended by a complete vectorlike family, precise top, bottom and tau Yukawa coupling unification can be achieved assuming SUSY threshold corrections which are typical for comparable superpartner masses. Furthermore, the unification is possible with a large unified coupling, implying that all three fermion masses can be simultaneously close to their IR fixed points. Assuming unified Yukawa couplings of order one or larger, the preferred common scale of new physics (superpartners and vectorlike matter) is in the 3 TeV to 30 TeV range, with larger couplings favoring smaller scales. Splitting superpartner masses from masses of vectorlike fields, the preferred scales extend in both directions. The multi-TeV scale for superpartners is compatible with and independently suggested by the Higgs boson mass.
Highlights
Values of some of the free parameters in the standard model (SM) can be understood if they are related by additional symmetries to other parameters
We show that in the minimal supersymmetric extension of the standard model (MSSM) extended by a complete vectorlike family (MSSM þ 1VF), precise top, bottom and tau Yukawa coupling unification can be achieved with a large unified coupling, implying that all three fermion masses can be simultaneously close to their IR fixed points
The unification is possible assuming SUSY threshold corrections which are typical for comparable superpartner masses and no hierarchies or specific relations among SUSY parameters are required
Summary
Values of some of the free parameters in the standard model (SM) can be understood if they are related by additional symmetries to other parameters. A split spectrum of vectorlike matter (e.g., the spectrum obtained from the RG evolution starting with a unified vectorlike mass term at the GUT scale, MV1616) would result in logarithmic threshold corrections to the third generation Yukawa couplings.. The complete set of SUSY threshold corrections to the third generation Yukawa couplings (for which the approximate formulas can be found above) is included at thpeffiffiMSUSY scale [5,6,7,27,57] with the assumption that μ 1⁄4 − 2MSUSY (we will see that only the negative sign is consistent with Yukawa coupling unification assuming comparable superpartner masses). When fitting the central values of gauge couplings and fermion masses we use as an input: α−EM1 ðMZÞ 1⁄4 127.955, sin2θW 1⁄40.2312, α3ðMZÞ 1⁄4 0.1181, mt 1⁄4173.1GeV, mbðmbÞ1⁄44.18 GeV and mτ 1⁄4 1.777 GeV, where mt and mτ are pole masses [58]
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