Study Of The Origin Of Nonzero θ₁₃ And The Violation Of Lepton Flavor Universality

"Science" announced the top ten scientific breakthroughs of the year2012and pointed out that:if LHC researchers do not find new particles beyond those in the standard model, then neutrino physics could be the future of particle physics.From Pauli’s neutrino conjecture in1930to the experimental discovery of neutrino oscillation in1998, and then to the subsequent series of neutrino experiments, the neutri-no physics gets great progress. From ultra-high-energy neutrino in cosmic rays to atmo-spheric neutrino, solar neutrino, supernova neutrino, and then to the matter-antimatter asymmetry in the Universe, dark matter and the evolution in the early Universe, all these make neutrino play a more and more important role in the study of astronomy and cosmology. MSW resonance succeeded in solving solar neutrino problem; The mea-surement of atmospheric ve and vμ provided powerful evidence for neutrino oscillation; In order to accommodate the anomalies in experiments, for instance, LSND anomaly, reactor antineutrino anomaly et al., sterile neutrinos are introduced in phenomenology models. The study of neutrino physics has correlation with theoretical physics, experi-ments of particle physics, astronomy and cosmology and becomes a active and exciting field.Based on the development of neutrino experiments, neutrino physics, astronomy and cosmology are showing repaid progress. Many aspects of neutrino physics are being studied and payed close attention. For instance, the origin of neutrino mass generation, seesaw mechanism, neutrino mixing, neutrino physics under high-energy scales, sym-metries concerning neutrino, the existence of sterile neutrino and its influence on the standard model neutrino, CP violation, ultra-high-energy neutrino, neutrino and dark matter, the effect of neutrino in the evolution of the Universe, et al.Current neutrino experiments provide definite evidence about the existence of neu-trino oscillation. This is the sole new physics beyond standard model which is con-firmed by experiments. The existence of neutrino oscillation requires that neutrinos are massive, they do mix and the mass-squared differences among them are relative-ly small. Among the three mixing angles depicting neutrino mixing,θ13is the last quantity which is least known and in some theories, its value is assumed to be ze-ro. In2012, Daya Bay collaboration released the precise measurement value of θ13: sin22θ13=0.089±0.010(stat)±0.005(syst).In order to accommodate the neutrino mixing angles, there arise lots of theories, for instance,μ-τsymmetry, A4family symmetry, quark-lepton complementarity, et al. However, the precise measurements of θ13and θ23indicate that there exist deviations between these schemes and the results from experiments.Recently, the result from accelerator experiment MINOS indicates that θ23is not the originally assumed45°. Then the next task of neutrino physics is to fix the problem of θ23>45°or θ23<45°, i.e. the octant of θ23.In this thesis we mainly study the issue about the origin of non-zero θ13, and also discuss the application of matter effect of neutrino and the violation of lepton flavor universality.1. There exist some symmetries for the neutrino mixing under high-energy scales. During the evolution to low-energy scale, these symmetries are broken to obtain the real mixing pattern which is consistent with the experimental results. There arise lots of mixing patterns which possess some symmetries. These models provide unfitted results about the mixing angles, e.g., the vanished θ13. We try to theoretically study the origin of non-zero θ13to obtain the viable mixing parameters which are consistent with the current neutrino oscillation experiments:(1) Based on Friedberg and Lee’s geometric picture by which the tribimaximal PMNS leptonic mixing matrix is constructed, namely corresponding mixing angles cor-respond to the geometric angles among the sides of a cube, we suggest that the three realistic mixing angles which slightly deviate from the values determined for the cube, are due to a viable deformation from the perfectly cubic shape. Taking the best fitted results of θ12and θ23as inputs, we determine the central value of θ13, which is consistent with the T2K experimental result.(2) The PMNS matrix displays an obvious symmetry, but not exact. There are sev-eral textures proposed in literature, which possess various symmetry patterns and seem to originate from different physics scenarios at high energy scales. To be consistent with the experimental measurement, all of the regularities slightly decline, i.e. the symmetry must be broken. Following the schemes given in literature, we modify the matrices (9in total) to gain the real PMNS matrix by perturbative rotations. The transformations may provide hints about the underlying physics at high energies and the breaking mech- anisms which apply during the evolution to the low energy scale, especially the results may be useful for the future model builders.(3) In order to accommodate the experimental anomalies, sterile neutrinos are in-troduced. If there exists mixing between sterile neutrinos and active ones, then this mixing can have an influence on the mixing parameters of active neutrinos. In theory, these influence provides the possibility from the symmetric patterns to the real mixing matrix and obtaining non-zero θ13. Taking this as the starting point, we discuss the possibility of obtaining the real mixing matrix by the introducing of sterile neutrino.2. The introducing of sterile neutrino not only accommodates the experimental anomalies, but also has relation with the experimental signals of new physics and pro-vides an accommodation to the latter. The recent measurements on Rk and Rπ imply that there exists a possible violation of the leptonic flavor universality which is one of the cornerstones of the standard model. It is suggested that a mixing between sterile and active neutrinos might induce such a violation. We consider the scenarios with one or two sterile neutrinos to explicitly realize the data while the constraints from the available experiments have been taken into account. Moreover, as indicated in lit-erature, the deviation of the real PMNS matrix from the symmetric patterns may be due to a μ-τ asymmetry, therefore the measurements on RD(Ds)eμ=Γ(D(DS)→e+ve)/Γ(D(Ds)→μ+vμ and RD(Ds)μτ=Γ(D(Ds)→μ+vμ)/Γ(D(Ds)→μ+ττ (and for some other heavy mesons B±and Bc etc.) may shed more light on physics responsible for the violation of the leptonic flavor universality. The data of BES III are available to test the universality and that of the future charm-tau factory will provide more accurate information towards the aspect, in this work, we discuss RD(Ds)eμ and RD(Ds)μτ in all details and also briefly consider the cases for B±and Bc3. Earthquakes and tsunamis are natural catastrophes.. They occur in our globe so frequently and cost thousands of lives and immense loss of properties. The knowl-edge on modern physics and sophisticated detection techniques and facilities may help, as we believe. We discuss the possibility of forecasting earthquakes by means of (an-ti)neutrino tomography. Antineutrinos emitted from reactors are used as a probe. As the antineutrinos traverse through a region prone to earthquakes, observable variations of the matter effect on the antineutrino oscillation would provide a tomography of the vicinity of the region. In this preliminary work, we adopt a simplified model for the geometrical profile and matter density in a fault zone. We calculate the survival proba-bility of electron antineutrinos for cases without and with an anomalous accumulation of electrons which can be considered as a clear signal of the coming earthquake, at the geological region with a fault zone and find that the variation may reach as large as8.5%for ve emitted from a reactor. The case for a ve beam from a neutrino factory is also investigated, and it is noted that, because of the typically high energy associated with such neutrinos, the oscillation length is too large and the resultant variation is not practically observable. Our conclusion is that an intense neutrino source with energies similar to reactor neutrinos and improved detector sensitivity are needed for realizing this scheme.