Supersymmetry and Unification: Heavy Top Was the Key

Understand

I review the unification of gauge couplings of strong, weak and electro-magnetic interactions.

• I start by recalling the history of the most important prediction of low-energy supersymmetry: the correct value of the weak mixing angle tied to a large top quark mass.
• I then turn to the discussion of the present day situation of the minimal supersymmetric Grand Unified Theories based on SU(5) and SO(10) groups, and I show why the minimal SU(5) is in accord with experiment.
• For the sake of completeness I also summarize the problems and possible solutions of the minimal ordinary SU(5).