CP violation in the neutrino sector: The new frontier

The discovery of neutrino masses has revealed a new flavour sector in the Standard Model. Just like the quark flavour sector, it contains a seed of CP violation, resulting in an asymmetric behaviour of matter and antimatter. It is argued that this new source of leptonic CP violation may be discovered in more precise neutrino oscillation experiments involving neutrino beams with energies in the GeV range that will be sent to distances of a few thousand kilometres.     

Threshold effects on renormalization group running of neutrino parameters in the low-scale seesaw model

We show that, in the low-scale type-I seesaw model, renormalization group running of neutrino parameters may lead to significant modifications of the leptonic mixing angles in view of so-called seesaw threshold effects. Especially, we derive analytical formulas for radiative corrections to neutrino parameters in crossing the different seesaw thresholds, and show that there may exist enhancement factors efficiently boosting the renormalization group running of the leptonic mixing angles. We find that, as a result of the seesaw threshold corrections to the leptonic mixing angles, various flavor symmetric mixing patterns (e.g., bi-maximal and tri-bimaximal mixing patterns) can be easily accommodated at relatively low energy scales, which is well within the reach of running and forthcoming experiments (e.g., the LHC).     

Neutrino unification

Present neutrino data are consistent with neutrino masses arising from a common seed at some "neutrino unification" scale M(X). Such a simple theoretical ansatz naturally leads to quasidegenerate neutrinos that could lie in the electron-volt range with neutrino mass splittings induced by renormalization effects associated with supersymmetric thresholds. In such a scheme the leptonic analog of the Cabibbo angle straight theta(middle dot in circle) describing solar neutrino oscillations is nearly maximal. Its exact value is correlated with the smallness of straight theta(reactor). The two leading mass-eigenstate neutrinos present in nu(e) form a pseudo-Dirac neutrino, avoiding conflict with neutrinoless double beta decay.     

Effect on Jarlskog Determinant Above the GUT Scale Within Four Flavor Neutrino Framework

We study the Planck scale effects on Jarlskog determiant in the four flavor framework. On electroweak symmetry breaking, quantum gravitational effects lead to an effective SU(2) × U(1) invariant dimension-5 Lagrangian including neutrino and Higgs forces, which perturbed the neutrino mass term and produce an extra terms in the neutrino mass matrix. We consider that gravitational interaction is independent from flavor and compute the Jarlskog determiant due to Planck scale effects. In the case of leptonic sector, the strentgh of CP violation is measured by Jarlskog determiant. We applied our approach to study Jarlskog determinant in the four flavor neutrino mixing above the GUT scale.

     

Leptonic flavor and CP violation

Recent neutrino oscillation data teach us that the neutrinos have masses and that they mix. We discuss two ways that can be used to probe other non-standard leptonic physics. We show that non-standard neutrino interaction can be probed in neutrino oscillation experiments and discuss sneutrino-antisneutrino mixing.     

Mass and CKM matrices of quarks and leptons, the leptonic CP-phase in neutrino oscillations

A general approach for construction of quark and lepton mass matrices is formulated. The hierarchy of quarks and charged leptons (“electrons”) is large, it leads using the experimental values of mixing angles to the hierarchical mass matrix slightly deviating from the ones suggested earlier by Stech and including naturally the CP-phase.

The same method based on the rotation of generation numbers in the diagonal mass matrix is used in the electron–neutrino sector of theory, where neutrino mass matrix is determined by the Majorano see-saw approach. The hierarchy of neutrino masses, much smaller than for quarks, was used including all existing (even preliminary) experimental data on neutrino mixing.

The leptonic mass matrix found in this way includes the unknown value of the leptonic CP-phase. It leads to large ν_μν_τ oscillations and suppresses the ν_eν_τ and also ν_eν_μ oscillations. The explicit expressions for the probabilities of neutrino oscillation were obtained in order to specify the role of leptonic CP-phase. The value of time reversal effect (proportional to sin δ′) was found to be small 1%. However, a dependence of the values of ν_eν_μ,ν_eν_τ transition probabilities, averaged over oscillations, on the leptonic CP-phase has found to be not small – of order of ten percent.     

True Neutrality as a New Type of Flavour

A classification of leptonic currents with respect to C-operation requires the separation of elementary particles into the two classes of vector C-even and axial-vector C-odd character. Their nature has been created so that to each type of lepton corresponds a kind of neutrino. Such pairs are united in families of a different C-parity. Unlike the neutrino of a vector type, any C-noninvariant Dirac neutrino must have his Majorana neutrino. They constitute the purely neutrino families. We discuss the nature of a corresponding mechanism responsible for the availability in all types of axial-vector particles of a kind of flavour which distinguishes each of them from others by a true charge characterized by a quantum number conserved at the interactions between the C-odd fermion and the field of emission of the corresponding types of gauge bosons. This regularity expresses the unidenticality of truly neutral neutrino and antineutrino, confirming that an internal symmetry of a C-noninvariant particle is described by an axial-vector space. Thereby, a true flavour together with the earlier known lepton flavour predicts the existence of leptonic strings and their birth in single and double beta decays as a unity of flavour and gauge symmetry laws. Such a unified principle explains the availability of a flavour symmetrical mode of neutrino oscillations.     

Neutrino masses from three-particle decays

The purely leptonic decays of the tau and the radiative decay of the pion provide determinations of the tau neutrino and muon neutrino masses, respectively. The shift of the energy at which the tau decay spectrum attains its maximum and the forward-backward ratio are both large enough to determine tau neutrino masses of about 100 MeV. The photon endpoint energy and partially integrated differential decay rate in pion decay are sensitive to a neutrino mass as small as 100 keV. Thus, the present bounds on neutrino masses can be significantly improved.     

Jets in neutrino deep inelastic scattering

Jet cross sections are calculated to first order in QCD for neutrino production. We give thrust and spherocity distributions and calculate angular correlations between jet and leptonic planes.     

Leptonic CP-violation and mirror leptons

We study leptonic CP-violation within a single fermion generation in an extended electro-weak model where new right-handed leptons, so-called mirror leptons, exist and mix with standard left-handed leptons. Essential differences are pointed out between the mixing of a left-handed neutrino with a mirror neutrino in such a model and the ordinary mixing of two left-handed neutrinos in the standard model. E.g. in the mirror case CP-violation may occur even if neutrinos are Dirac particles. The number of physical CP-violation phases is determined for different mixing schemes and parameterizations of the leptonic weak currents in terms of these phases are presented.     

Spontaneous R parity violation in supersymmetry: A model for solar neutrino oscillations

Spontaneous breaking of R parity in the standard supergravity model implies the existence of a majoron which is strongly constrained by astrophysics. This is suggested as the origin of the small parameter required for the resonant amplification of neutrino oscillations to take place in the sun. To a good approximation only one neutrino type (most likely the tau neutrino) acquires a mass. Therefore the form of the leptonic charged current is very much restricted: it is fully described by two mixing angles and there is no CP violation. As a result, matter can only amplify oscillations in one channel which, for small mixings, is v_ℓv_τ. Agreement with the chlorine data on the one hand and the nonobservation of charged supersymmetric states in e⁺e^- collisions on the other, tightly restricts the parameters of the model in a way that will be directly tested by collider experiments.     

Neutrino Mixing in Matter at Extreme High Energy

We have studied neutrino mixing at extreme high energy considering two flavour framework with matter effects. We analyze the atmospheric neutrino data within the simplest scheme of two neutrino oscillation. We consider as special case of matter density profile, which are relevant for neutrino oscillations. In particular, we compute to constrain a specific from of neutrino mass square difference and mixing in extreme high energy in matter. The dispersion relation for the neutrino mixing in neutrino oscillation in matter are discussed.     

CP phases in the charged current and Higgs sectors for Majorana neutrinos

The diagonalization of the leptonic mass matrices is performed in the framework of the triplet model to generate Majorana mass terms for neutrinos. This allows the understanding of the role played by the CP-violating phases in the Higgs sector and their relation with those of the charged-current Lagrangian. It is shown that all the leptonic mixings, including those of the Higgs couplings, can be given in terms of a Kobayashi-Maskawa matrix and the relative Majorana phases of the neutrino fields. The characteristic Majorana phases, always appearing together with the neutrino mass, are present in |ΔL|=2 pieces and they show up in processes with a) neutrino-antineutrino propagation, and/or b) at least two different neutrinos as asymptotic states, and/or c) a vertex with a doubly-charged scalar. The phenomenological implications for processes with these characteristics are given.     

Neutrino mixing and leptonic CP phase in neutrino oscillations

Oscillations of the Dirac neutrinos of three generations in vacuum are considered with allowance made for the effect of the CP-violating leptonic phase (analogue of the quark CP phase) in the lepton mixing matrix. The general formulas for the probabilities of neutrino transition from one sort to another in oscillations are obtained as functions of three mixing angles and the CP phase. It is found that the leptonic CP phase can, in principle, be reconstructed by measuring the oscillation-averaged probabilities of neutrino transition from one sort to another. The manifestation of the CP phase as a deviation of the probabilities of direct processes from those of inverse processes is an effect that is practically unobservable as yet.     

Further limits on heavy neutrino couplings

Limits on leptonic mixing matrix elements are inferred from the results of a dedicated neutrino-decay search; an improvement of more than two orders of magnitude is achieved over previous results for a wide range of the neutrino mass.     

A method to limit the muon neutrino mass

Existence of a purely leptonic neutral current weak interaction may permit the use of ν_ω, e^? elastic scattering to limit the muon neutrino mass.     

Knitting neutrino mass textures with or without Tri-Bi maximal mixing

The solar and baseline neutrino oscillation data suggest bimaximal neutrino mixing among the first two generations, and trimaximal mixing between all three neutrino flavors. It has been conjectured that this indicates the existence of an underlying symmetry for the leptonic fermion mass textures. The experimentally measured quantities, however, are associated to the latter indirectly and in a rather complicated way through the mixing matrices of the charged leptons and neutrinos. Motivated by these facts, we derive exact analytical expressions which directly link the charged lepton and neutrino mass and mixing parameters to measured quantities and obtain constraints on the parameter space. We discuss deviations from Tri-Bi mixing matrices and present minimal extensions of the Harrison, Perkins and Scott matrices capable of interpreting all neutrino data.     

No collective neutrino flavor conversions during the supernova accretion phase

We perform a dedicated study of the supernova (SN) neutrino flavor evolution during the accretion phase, using results from recent neutrino radiation hydrodynamics simulations. In contrast to what was expected in the presence of only neutrino-neutrino interactions, we find that the multiangle effects associated with the dense ordinary matter suppress collective oscillations. The matter suppression implies that neutrino oscillations will start outside the neutrino decoupling region and therefore will have a negligible impact on the neutrino heating and the explosion dynamics. Furthermore, the possible detection of the next galactic SN neutrino signal from the accretion phase, based on the usual Mikheyev-Smirnov-Wolfenstein effect in the SN mantle and Earth matter effects, can reveal the neutrino mass hierarchy in the case that the mixing angle θ(13) is not very small.     

Neutrino hierarchy from CP-blind observables with high density magnetized detectors

High density magnetized detectors are well suited to exploit the outstanding purity and intensities of novel neutrino sources like neutrino factories and beta beams. They can also provide independent measurements of leptonic mixing parameters through the observation of atmospheric muon-neutrinos. In this paper, we discuss the combination of these observables from a multi-kT iron detector and a high energy beta beam; in particular, we demonstrate that even with moderate detector granularities the neutrino mass hierarchy can be determined for θ₁₃ values greater than 4°. PACS 14.60.Pq; 14.60.Lm