Phenomenological Study On Combination Of μ-τ Reflection Symmetry And Tezture Zeros In Minimal Seesaw Model

The solar,atmospheric,reactor and accelerator neutrino oscillation experiments provide us with strong evidence that neutrinos have tiny masses and flavor mixing.This major discovery opens a new window into new physics beyond the Standard Model（SM）.Of all the mechanisms that explain the origin of the tiny mass of neutrinos,the seesaw mechanism can not only naturally explain the tiny mass of neutrinos,but also explain the asymmetry of matter and antimatter in the universe through the leptogenesis mechanism.Before the neutrino flavor mixing angle θ₁₃ was determined,people were inspired by the fact that the neutrino flavor mixing angles at that time θ₁₂,θ₂₃ approached the special value(sin²θ₁₂≈1/3,sin²θ₂₃≈1/2)and believed that θ₁₃ also approached the special value(θ₁₃ ≈0°),the model based on this ideal case is called tri-bimaximal（TBM）mixing.The Daya Bay experiment gives the experimental results of the mixing angle θ₁₃（?）9°,forcing people to modify the TBM mixing to be compatible with the current experimental data,thus obtaining the TM₁ and TM₂ mixing.In addition,considering that the flavor mixing angle θ₂₃ and the Dirac CP phase（δ≈-π/2）approach special values,one speculates that there may be some flavor symmetry in the lepton sector.Among them μ-τ reflection symmetry is one of the currently favored flavor symmetry models.To enhance the predictive power of the seesaw model,and taking into account the two non-zero neutrino mass squared differences and the minimum number of right-handed neutrinos required for successful leptogenesis is two,this thesis only focuses on the minimal seesaw model with two right-handed neutrinos on the basis of the standard model（at this time the lightest neutrino has zero mass）.Even so,the minimum seesaw model still has more parameters than the low-energy neutrino observable measurements.In order to obtain a testable prediction,it is necessary to further reduce its parameters.In this thesis,we study the simplified structure of the phenomenologically feasible MD（with structure zero）and its effect on leptogenesis.Our study was conducted in two specific flavor symmetry patterns:（1）μ-τ reflection symmetry;（2）μ-τreflection symmetry combined with TM₁ mixing.First of all,in the basis of the right-handed neutrino mass matrix being diagonal,we research the special structure of MD that can naturally realize the μ-τ reflection symmetry and impose constraints on it（structure zero）,and then analyze the effect of this model on neutrino parameters as well as leptogenesis.By calculating the leptogenesis results we find that leptogenesis can proceed successfully only in the cases where M₁<M₂、η=+1 and the neutrino masses ordered in normal ordering.Furthermore the special structure of the TM₁ mixing and μ-τ reflection symmetry and its phenomenological are also studied.The model parameters are reduced by imposing the constraint-structure zero,and according to the model parameters values we investigate the effect of the model on leptogenesis.It is calculated and found that only in the case where M₁<M₂ and η=+1 successful leptogenesis can be achieved.