title: Nonanomalous discrete R symmetry decrees three generations.
abstract: We show that more than two generations of quarks and leptons are required to have an anomaly free discrete R symmetry larger than R parity, provided that the supersymmetric standard model can be minimally embedded into a grand unified theory. This connects an explanation for the number of generations with seemingly unrelated problems such as supersymmetry breaking, proton decay, the μ problem, and the cosmological constant through a discrete R symmetry. We also show that three generations is uniquely required by a nonanomalous discrete R symmetry in classes of grand unified theories such as the ones based on (semi)simple gauge groups.
authors.affiliation: IPMU, University of Tokyo, Kashiwa 277-8568, Japan.
authors.forename: Jason L
authors.initials: JL
authors.lastname: Evans
authors.forename: Masahiro
authors.initials: M
authors.lastname: Ibe
authors.forename: John
authors.initials: J
authors.lastname: Kehayias
authors.forename: Tsutomu T
authors.initials: TT
authors.lastname: Yanagida