Gauge coupling unification,the GUT scale,and magic fields

We consider field sets that do not form complete SU(5) multiplets, but exactly preserve the one-loop MSSM prediction for α₃(MZ)${\alpha }_3(M_Z)$ independently of the value of their mass. Such fields can raise the unification scale in different ways, through a delayed convergence of the gauge couplings, a fake unified running below the GUT scale, or a postponed unification after a hoax crossing at a lower scale. The α₃(MZ)${\alpha }_3(M_Z)$ prediction is independent of the mass of the new fields, while the GUT scale often is not, which allows to vary the GUT scale. Such “magic” fields represent a useful tool in GUT model building. For example, they can be used to fix gauge coupling unification in certain two step breakings of the unified group, to suppress large KK thresholds in models with extra dimensions, or they can be interpreted as messengers of supersymmetry breaking in GMSB models.     

Simple and direct communication of dynamical supersymmetry breaking

Journal of High Energy Physics - It was shown in a previous study that a lightest neutralino with mass below 30 GeV was severely constrained in the minimal supersymmetric standard model (MSSM),...