Narrow Results

It is shown that Lorentz invariance implies that in general flavor neutrinos in oscillation experiments are superpositions of massive neutrinos with different energies and different momenta. It is also shown that for each process in which neutrinos are produced, there is either a Lorentz frame in which all massive neutrinos have the same energy or a Lorentz frame in which all massive neutrinos have the same momentum. In the case of neutrinos produced in two-body decay processes, there is a Lorentz frame in which all massive neutrinos have the same energy.

It is shown that the 99% confidence limits from the analyses of the data of cosmological and neutrino experiments imply a small marginally allowed region in the space of the neutrino oscillation parameters of 3 + 1 four-neutrino mixing schemes. This region can be confirmed or falsified by experiments in the near future.

In the recent years important discoveries in the field of low energy neutrino physics (E_ν in the ≈ MeV range) have been achieved. Results of the solar neutrino experiment SNO show clearly flavor transitions from ν_e to ν_μ,τ. In addition, the long standing solar neutrino problem is basically solved. With KamLAND, an experiment measuring neutrinos emitted from nuclear reactors at large distances, evidence for neutrino oscillations has been found. The values for the oscillation parameters, amplitude and phase, have been restricted. In this paper the potential of future projects in low energy neutrino physics is discussed. This encompasses future solar and reactor experiments as well as the direct search for neutrino masses. Finally the potential of a large liquid scintillator detector in an underground laboratory for supernova neutrino detection, solar neutrino detection, and the search for proton decay p→K⁺ν is discussed.

The major steps in the development of our knowledge about neutrinos are reviewed. The basics of neutrino oscillation formalism is presented. Neutrino oscillations in the framework of three-neutrino mixing are considered. The evidence for neutrino oscillations is discussed. Neutrinoless double β-decay is briefly considered.

If a family symmetry exists for the quarks and leptons, the Higgs sector is expected to be enlarged to be able to support the transformation properties of this symmetry. There are, however, three possible generic ways (at tree level) of hiding this symmetry in the context of the Standard Model with just one Higgs doublet. All three mechanisms have their natural realizations in the unification symmetry E₆ and one in SO(10). An interesting example based on SO(10)×A₄ for the neutrino mass matrix is discussed.

The pp interactions taking place in the cosmos around us are a source of the astrophysical neutrinos of all the three flavors. In these interactions, the electron and the muon neutrinos mainly come from the production and the decay of the π^± mesons, whereas the tau neutrinos mainly come from the production and the decay of the mesons. We estimate the three intrinsic neutrino flavor ratios for 1 GeV ≤E≤10¹² GeV in the pp interactions and found them to be 1:2:3×10^-5. We study the effects of neutrino oscillations on these intrinsic ratios. We point out that the three ratios become 1:1:1 if L(pc)/E(GeV)≥10^-10 in the presence of neutrino oscillations, where L is the distance to the astrophysical neutrino source in units of parsecs.

The discrete subgroup Δ(27) of SU(3) has some interesting properties which may be useful for understanding charged-lepton and neutrino mass matrices. Assigning leptons to the 3 and representations of Δ(27), a simple form of the Majorana neutrino mass matrix is obtained and compared to present data.

We analyze with the Bayesian method the solar and KamLAND neutrino data in terms of neutrino oscillations. We show that Bayesian credible regions with a flat prior in the plane strongly support the LMA solution, in agreement with the usual chi-square analysis. Other reasonable priors are considered in order to test the stability of the LMA solution. We show that priors which favor small or large values of the mixing angle lead to minor changes of the allowed LMA region, affecting mainly its large-tan²θ₁₂ part.

In the recent successful applications of the non-Abelian discrete symmetry A₄ to the tribimaximal mixing of neutrinos, lepton doublets and singlets do not transform in the same way. It thus appears to be unsuitable as a family symmetry in grand unification. A simple resolution of this dilemma is proposed.

Assuming the existence of one light sterile neutrino, we investigate the neutrino flavor mixing matrix in matter. Sum rules between the mixing parameters in vacuum and their counterparts in matter are derived. By using these new sum rules, we obtain the simple but exact expressions of the effective flavor mixing matrix in matter in terms of neutrino masses and the mixing parameters in vacuum. The rephasing invariants, sides of unitarity quadrangles and oscillation probabilities in matter are also achieved. Our model-independent results will be very helpful for analyzing flavor mixing and CP violation in the future long-baseline neutrino oscillation experiments.

In an improved application of the tetrahedral symmetry A₄ first introduced by Ma and Rajasekaran, supplemented by the discrete symmetry Z₃ as well as supersymmetry, a two-parameter form of the neutrino mass matrix is derived which exhibits the tribimaximal mixing of Harrison, Perkins and Scott. This form is the same as the one obtained previously by Altarelli and Feruglio, and the inverse of that obtained by Babu and He. If only A₄ is used, then corrections appear, making tan² θ₁₂ different from 0.5, without changing significantly sin²2θ₂₃ from one or θ₁₃ from zero.

We consider the µ - τ symmetric Friedberg-Lee (FL) symmetry for the neutrino sector and show that a specific FL translation leads to the tribimaximal mixing pattern of the Maki-Nakagawa-Sakata (MNS) matrix. We also apply the symmetry to the type-I seesaw framework and address the baryon asymmetry of the universe through the leptogenesis mechanism. We try to establish a relation between the net baryon asymmetry and CP phases included in the MNS matrix.

Neutrino tribimaximal mixing is obtained from the breaking of A₄ to Z₃ in the charged-lepton sector and to Z₂ in the neutrino sector. To enforce this conflicting pattern, extra particles and symmetries are usually invoked, often accompanied by nonrenormalizable interactions and even extra dimensions. It is shown here in a specific renormalizable model how A₄ alone will accomplish this, with only the help of lepton number.

We study an effective gauge theory whose gauge group is a semidirect product G = G_c ⋊ Γ with G_c and Γ being a connected Lie group and a finite group, respectively. The semidirect product is defined through a projective homomorphism (i.e. homomorphism up to the center of G_c) from Γ into G_c. To be specific, we take SU(3)_L as G_c and ℤ₃ × ℤ₃ as Γ. We notice that the irreducible representations of the gauge group G necessarily contain three G_c-multiplets in spite of the Abelian nature of Γ = ℤ₃ × ℤ₃. This triplication phenomenon is due to the semidirect product structure of G. We suggest that the appearance of three families is attributable to this triplication. We give a toy model on the lepton mixing and show that under a particular vacuum alignment the tri-bimaximal mixing matrix is reproduced.

Global fits to neutrino oscillation data are compatible with tri-bimaximal mixing pattern, which predict θ₂₃ = π/4, and θ₁₃ = 0. We propose here to parametrize the tri-bimaximal mixing matrix V_TBM by its hermitian generator H_TBM using the exponential map. Then we use the exponential map to express the deviations from tri-bimaximal pattern by deriving the hermitian matrices H_{z = 0} and H₁. These deviations might come from the symmetry breaking of the neutrino and charged lepton sectors.

In this document we will review the current status of reactor neutrino oscillation experiments and present their physics potentials for measuring the θ₁₃ neutrino mixing angle. The neutrino mixing angle θ₁₃ is currently a high-priority topic in the field of neutrino physics. There are currently three different reactor neutrino experiments, DOUBLE CHOOZ, DAYA BAY and RENO and a few accelerator neutrino experiments searching for neutrino oscillations induced by this angle. A description of the reactor experiments searching for a nonzero value of θ₁₃ is given, along with a discussion of the sensitivities that these experiments can reach in the near future.

In this brief review we discuss the generation of Majorana neutrino masses through the seesaw mechanism, the theory of neutrinoless double-beta decay, the implications of neutrino oscillation data for the effective Majorana mass, taking into account the recent Daya Bay measurement of ϑ₁₃, and the interpretation of the results of neutrinoless double-beta decay experiments.

We introduce a 2–3 symmetric structure of the charged lepton mass matrix except for one breaking by the muon mass. Symmetry breaking effects are provided both in the charged lepton and the neutrino sector to produce corrections to the leptonic mixing and explain the recent θ₁₃ measurements. A model that extends the SM by three right-handed neutrinos, an extra Higgs doublet, and multi-singlet scalars is introduced to generate the leptonic mixing.

It is argued that four-Fermi interactions induced by non-perturbative effects due to scattering of stringy matter from D-particles, D-instantons and more generally bulk gauge fields in brane models with large extra dimensions have, in specific situations, condensate structure described by flavor vacua.

We investigate the possibility of expressing the charged leptons and neutrino mass matrices as linear combinations of elements of a single finite group. Constraints imposed on the resulting mixing matrix by current data restrict the group types, but allow a nonzero value for the θ₁₃ mixing angle.