MSGUT: From bloom to doom

Abstract

By a systematic survey of the parameter space we confirm our surmise [C.S. Aulakh, MSGUTs from germ to bloom: Towards falsifiability and beyond, hep-ph/0506291] that the Minimal Supersymmetric GUT (MSGUT) based on the 210 ⊕ 126 ⊕ 126 ¯ ⊕ 10 Higgs system is incompatible with the generic Type I and Type II seesaw mechanisms. The incompatibility of the Type II seesaw mechanism with this MSGUT is due to its generic extreme sub-dominance with respect to the Type I contribution. The Type I mechanism although dominant over Type II is itself unable to provide neutrino masses larger than ∼ 10 −3 eV anywhere in the parameter space. Our Renormalization Group based analysis shows the origin of these difficulties to lie in a conflict between baryon stability and neutrino oscillation. The MSGUT completed with a 120-plet Higgs is the natural next to minimal candidate. We propose a scenario where the 120-plet collaborates with the 10-plet to fit the charged fermion masses. The freed 120-plet couplings can then give sub-dominant contributions to charged fermion masses and enhance the Type I seesaw masses sufficiently to provide a viable seesaw mechanism. We give formulae required to verify this scenario.