On Yukawa quasi-unification with µ < 0

The constrained minimal supersymmetric standard model (CMSSM), which is a predictive version of the minimal supersymmetric standard model (MSSM) based on universal boundary conditions, can be further restricted by being embedded in a supersymmetric (SUSY) grand unified theory (GUT) with a gauge group containing SU(4)c and SU(2)R. This can lead [1] to Yukawa unification [2], i.e., the exact unification of the third generation ‘asymptotic’ Yukawa couplings. However, for both signs of the MSSM parameter µ, the CMSSM supplemented by the assumption of exact Yukawa unification yields unacceptable values of the b-quark mass. This is due to the generation of sizeable SUSY corrections to mb [3] which have the sign of µ. The predicted treelevel mb(MZ), which turns out to be close to the upper edge of its 95% confidence level (c.l.) experimental range 2.684 − 3.092 GeV, receives, for µ > 0 (µ < 0), large positive (negative) corrections which drive it well above (a little below) the allowed range. This range is derived from the 95% c.l. range for mb(mb) in the MS scheme 3.95 −4.55 GeV [4] evolved up to MZ in accord with the