Researches On Generation And Matrix Structure Of Neutrino Masses

Neutrinos are among the most important and mysterious particles in nature.They play an essential role in nuclear physics,particle physics,astronomy and cosmology.The neutrino oscillation phenomenon suggests that neutrinos are massive and mixed.In recent years,the three mixing angles and the sizes of two neutrino mass-squared differences have been accurately measured.The neutrino mass ordering and Dirac CP phase are expected to be clarified in the near future.The origin of small neutrino masses and mixing pattern remains unknown,and could reveal some new mass generation methods besides the Higgs mechanism.Furthermore,as weakly interacting particles,neutrinos may also provide a portal for approaching the dark sector.The seesaw mechanisms which realize the dimension-five Weinberg operator at the tree level provide natural and attractive explanations for the smallness of the neutrino masses.Un-fortunately,the scales of the conventional seesaw mechanisms are too high to be accessed by current or planned high energy colliders.A common method to lower the scale of the under-lying model is to push the mass operator to higher dimensions.In this paper,we consider a generalized seesaw model of this kind.This model contains a particular triply charged lepton which can produce multi-lepton signals at colliders.We discuss the production of this triply charged lepton at the LHC.It is interesting that the measured mixing angle ?23 and the best fit value of Dirac CP phase ? are close to the special values ?/4 and-?/2,respectively.These remarkable relations may imply a flavor symmetry in the neutrino sector.The neutrino ?-?reflection symmetry has been attracting a lot of attention recently as it can naturally lead us to?23=?/4 and ?=-?/2.On the other hand,the minimal seesaw can settle the neutrino mass spectrum.In this paper,we attempt to implement the neutrino ?-? reflection symmetry in the minimal seesaw.For the experimental hints towards ?23??/4 and some theoretical reasons,we particularly study the breakings of this symmetry.Since the neutrino ?-? reflection symme-try is not the only way to generate ?23=?/4 and ?=-?/2,we study other possible textures of neutrino mass matrix that can lead to such a result.Base on the obtained results,we perform a further study in two phenomenologically appealing contexts:one neutrino mass matrix being vanishing and the minimal seesaw framework.