Simplified Structures Of The Minimal Seesaw Neutrino Model

Although the Standard Model(SM)is very successful in describing all known elementary particles and their interactions,it does not shed light on the origin of neutrino masses.The dis-covery of neutrino oscillation indicates that neutrinos have non-zero masses.How to modify the SM to accommodate the small but non-zero masses of neutrinos becomes an urgent problem.Of the various ideas that have been proposed to generate neutrino masses,the seesaw mech-anism is the most popular because it naturally explains the minuscule mass of neutrinos.In addition,the seesaw mechanism can also explain the baryon asymmetry of the universe through the leptogenesis mechanism.This paper focuses on the most popular type-I seesaw model,which introduces three right-handed neutrinos on the basis of the SM.However,since the general seesaw model contains far more parameters than observables,it is impossible to provide quantitative predictions for the latter.Therefore,this paper focuses on the minimal seesaw model with greatly reduced parame-ters(only two right-handed neutrinos).However,even the minimal seesaw model still has more parameters than the low-energy neutrino observables.In order to obtain testable predictions,its parameters need to be further reduced.Therefore,the phenomenologically viable simplified structures of MD(with zero element or equality relation)and their implications for leptogenesis are studied in this paper.Our study is carried out for two special forms of MR:(A)the diagonal form of MR;(B)the diagonal elements of MR being zero.With the developments future of neutrino experiments,these structures will face direct test.