Supersymmetric unification and R symmetries
Seminar Room 1, Newton Institute
After reviewing some virtues and problems of the minimal supersymmetric standard model (MSSM), I will show that, if one demands anomaly freedom and fermion masses, only R symmetries can forbid the supersymmetric Higgs mass term mu. I will then prove that R symmetries are not available in conventional grand unified theories (GUTs) and argue that this prevents natural solutions to the doublet-triplet splitting problem in four dimensions. On the other hand, higher-dimensional GUTs do not suffer from this problem. I will briefly discuss an explicit string-derived model in which the mu and dimension five proton decay problems are solved by an order four discrete R symmetry, and comment on the higher-dimensional origin of this symmetry.