Neutrino Mixing Angles Research Articles

Predictions for the neutrino parameters in the minimal model extended by linear combination of U(1)_{L_e-L_mu }, U(1)_{L_mu -L_tau } and U(1)_{B-L} gauge symmetries

We study the minimal extensions of the Standard Model by a linear combination of U(1)_{L_e-L_mu }, U(1)_{L_mu -L_tau } and U(1)_{B-L} gauge symmetries, where three right-handed neutrinos and one U(1)-breaking SU(2)_L singlet or doublet scalar are introduced. Because of the dependence on the lepton flavor, the structures of both Dirac and Majorana mass matrices of neutrinos are restricted. In particular, the two-zero minor and texture structures in the mass matrix for the active neutrinos are interesting. Analyzing these structures, we obtain uniquely all the neutrino parameters, namely the Dirac CP phase delta , the Majorana CP phases alpha _{2,3} and the mass eigenvalues of the light neutrinos m_i as functions of the neutrino mixing angles theta _{12}, theta _{23}, and theta _{13}, and the squared mass differences Delta m^2_{21} and Delta m^2_{31}. In 7 minimal models which are consistent with the recent neutrino oscillation data, we also obtain the predictions for the sum of the neutrino masses Sigma _i m_i and the effective Majorana neutrino mass langle m_{beta beta }rangle and compare them with the current experimental limits. In addition, we also discuss the implication of our results for leptogenesis.

Heavy sterile neutrino emission in core-collapse supernovae: constraints and signatures

Heavy sterile neutrinos with masses \U0001d4aa(100) MeV mixing with active neutrinos can be produced in the core of a collapsing supernova (SN). In order to avoid an excessive energy loss, shortening the observed duration of the SN 1987A neutrino burst, we show that the active-sterile neutrino mixing angle should satisfy sin2 θ ≲ 5 × 10−7. For a mixing with tau flavour, this bound is much stronger than the ones from laboratory searches. Moreover, we show that in the viable parameter space the decay of such “heavy” sterile neutrinos in the SN envelope would lead to a very energetic flux of daughter active neutrinos; if not too far below current limits, this would be detectable in large underground neutrino observatories, like Super-Kamiokande, as a (slightly time-delayed) high-energy bump in the spectrum of a forthcoming Galactic SN event.

Search for eV Sterile Neutrinos – The Stereo Experiment

In the recent years, major milestones in neutrino physics were accomplished at nuclear reactors: the smallest neutrino mixing angle θ13 was determined with high precision and the emitted antineutrino spectrum was measured at unprecedented resolution. However, two anomalies, the first one related to the absolute flux and the second one to the spectral shape, have yet to be solved. The flux anomaly is known as the Reactor Antineutrino Anomaly and could be caused by the existence of a light sterile neutrino eigenstate participating in the neutrino oscillation phenomenon. Introducing a sterile state implies the presence of a fourth mass eigenstate, while global fits favour oscillation parameters around sin2(2θ) = 0.09 and Δm2 = 1.8eV2.The Stereo experiment was built to finally solve this puzzle. It is one of the first running experiments built to search for eV sterile neutrinos and takes data since end of 2016 at ILL Grenoble, France. At a short baseline of 10 metres, it measures the antineutrino flux and spectrum emitted by a compact research reactor. The segmentation of the detector in six target cells allows for independent measurements of the neutrino spectrum at multiple baselines. An active-sterile flavour oscillation could be unambiguously detected, as it distorts the spectral shape of each cell’s measurement differently.This contribution gives an overview on the Stereo experiment, along with details on the detector design, detection principle and the current status of data analysis.

Testing texture two-zero neutrino mass matrices under current experimental scenario

The latest data from the Planck Collaboration presented an improved sensitivity limit of the sum of neutrino masses , at 95 confidence level (CL). On the other hand, the updated global fits of neutrino oscillation have shown a refined range of atmospheric mixing angle at the same CL. In the light of these observations, we have re-investigated the five viable cases (B1, 2, 3, 4 and C) of the texture two-zero Majorana mass matrix in the flavor basis. Using the present Planck's data, we have demonstrated that only cases B2 and B4 are now viable for normal mass ordering, while the remaining three cases do not meet the present experimental constraints at 2σ CL. The phenomenological predictions of the viable cases are also found to be in tune with the latest T2K, Super-Kamiokande and NOνA results, showing the preference for normal neutrino mass ordering (m1 < m2 < m3), a maximal Dirac CP-violating phase , and the upper octant of the neutrino mixing angle . In addition, the implication of Σ on the neutrinoless double beta decay is studied for viable cases.

Analysis of the reactor antineutrino spectrum anomaly with fuel burnup

Recently, three successful antineutrino experiments (Daya Bay, Double Chooz, and RENO) measured the neutrino mixing angle θ13; however, significant discrepancies were found, both in the absolute flux and spectral shape. Much effort has been expended investigating the possible reasons for the discrepancies. In this paper, the change of neutrino energy spectrum with burnup is analyzed from the point of view of the change of neutrino energy spectrum with burnup. An accurate method for calculating neutrino energy spectrum is proposed. The non-equilibrium correction is studied by using this method. It is found that the non-equilibrium correction contributes not only to the energy region less than 4.0 MeV, but also to the energy region greater than 4.0 MeV, with a maximum correction of about 3%.

Fitting neutrino masses in a realistic intersecting D-braneworld

The correct quark and charged lepton mass matrices along with a nearly correct CKM matrix may be naturally accommodated in a Pati-Salam model constructed from intersecting D6 branes on a $T^6/(\Z_2 \times \Z_2)$ orientifold. Furthermore, near-tribimaximal mixing for neutrinos may arise naturally due to the structure of the Yukawa matrices. Consistency with the quark and charged lepton mass matrices in combination with obtaining near-tribimaximal mixing fixes the Dirac neutrino mass matrix completely. Then, applying the seesaw mechanism for different choices of right-handed neutrino masses and running the obtained neutrino parameters down to the electroweak scale via the RGEs, we are able to make predictions for the neutrino masses and mixing angles. We obtain lepton mixing angles which are close to the observed values, $\theta_{12} =33.8^{\circ}\pm1.2^{\circ}$, $\theta_{23}=46.9^{\circ}\pm0.9^{\circ}$, and $\theta_{13}=8.56^{\circ}\pm0.20^{\circ}$. In addition, the neutrino mass-squared differences are found to be $\Delta m^2_{32} = 0.0025\pm0.0001$~eV$^2$ and $\Delta m^2_{21} = 0.000075\pm0.000003$~eV with $m_1=0.0150\pm0.0002$~eV, $m_2=0.0173\pm0.0002$~eV, and $m_3=0.053\pm 0.002$~eV so that $\sum_i m_i = 0.085\pm0.002$~eV, consistent with experimental observations.

Investigating the Sterile Neutrino Parameters with QLC in 3 + 1 Scenario

In the scenario with four generation quarks and leptons and using a 3+1 neutrino model having one sterile and the three standard active neutrinos with a 4×4 unitary transformation matrix, UPMNS4, we perform a model-based analysis using the latest global data and determine bounds on the sterile neutrino parameters i.e., the neutrino mixing angles. Motivated by our previous results, where, in a quark-lepton complementarity (QLC) model we predicted the values of θ13PMNS=9−2+2° and θ23PMNS=40.60−0.3+0.1°. In the QLC model the nontrivial correlation between CKM4 and PMNS4 mixing matrix is given by the correlation matrix Vc4. Monte Carlo simulations are performed to estimate the texture of Vc4 followed by the calculation of PMNS4 using the equation, UPMNS4=UCKM4·ψ4−1·Vc4, where ψ4 is a diagonal phase matrix. The sterile neutrino mixing angles, θ14PMNS, θ24PMNS and θ34PMNS are assumed to be freely varying between 0−π/4 and obtained results which are consistent with the data available from various experiments, like NovA, MINOS, SuperK, Ice Cube-DeepCore. In further investigation, we analytically obtain approximately similar ranges for various neutrino mixing parameters Uμ42 and Uτ42.

On the properties of the effective Jarlskog invariant for three-flavor neutrino oscillations in matter

In this paper, we show that the ratio of the effective Jarlskog invariant J˜ for leptonic CP violation in three-flavor neutrino oscillations in matter to its counterpart J in vacuum J˜/J≈1/(Cˆ12Cˆ13) holds as an excellent approximation, where Cˆ12≡1−2Aˆ⁎cos⁡2θ12+Aˆ⁎2 with Aˆ⁎≡acos2⁡θ13/Δ21 and Cˆ13≡1−2Accos⁡2θ13+Ac2 with Ac≡a/Δc. Here Δij≡mi2−mj2 (for ij=21,31,32) stand for the neutrino mass-squared differences in vacuum and θij (for ij=12,13,23) are the neutrino mixing angles in vacuum, while Δc≡Δ31cos2⁡θ12+Δ32sin2⁡θ12 and the matter parameter a≡22GFNeE are defined. This result has been explicitly derived by improving the previous analytical solutions to the renormalization-group equations of effective neutrino masses and mixing parameters in matter. Furthermore, as a practical application, such a simple analytical formula has been implemented to understand the existence and location of the extrema of J˜.

All fermion masses and mixings in an intersecting D-brane world

It is shown that neutrino mixing angles which are consistent with current experimental observations may be naturally obtained in a Pati-Salam model constructed from intersecting D6 branes on a T6/(Z2×Z2) orientifold. The Dirac mass matrices in the model are naturally the same as those which are obtained by imposing a Δ(27) flavor symmetry, which allows for near-tribimaximal mixing in the neutrino sector. In addition, it is possible to obtain the correct mass matrices for quarks and charged leptons, as well as nearly the correct CKM matrix. An RGE analysis of the neutrino mass parameters, including the seesaw mechanism assuming a specific form for the right-handed neutrino mass matrix is performed, and it is found that the neutrino mixing angles at the electroweak scale are θ12=35.0°, θ23=47.1°, and θ13=8.27°. In addition, the neutrino mass-squared differences are found to be Δm322=0.00252 eV2 and Δm212=0.0000739 eV2 with m1=0.0146 eV, m2=0.0170 eV, m3=0.0530 eV, and Σmi=0.0846 eV. These results depend slightly upon the scale at which the RGE running goes from being that of the MSSM to that of the SM, which we interpret to be the lightest stop mass. The best agreement with experimental data is for m˜t1≈4.28 TeV. This suggests that the superpartners which produce the strongest signal in a hadron collider are just out of reach at the LHC.

Fast neutrino flavor conversion: collective motion vs. decoherence

In an interacting neutrino gas, flavor coherence becomes dynamical and can propagate as a collective mode. In particular, tachyonic instabilities can appear, leading to “fast flavor conversion” that is independent of neutrino masses and mixing angles. On the other hand, without neutrino-neutrino interaction, a prepared wave packet of flavor coherence simply dissipates by kinematical decoherence of infinitely many non-collective modes. We reexamine the dispersion relation for fast flavor modes and show that for any wavenumber, there exists a continuum of non-collective modes besides a few discrete collective ones. So for any initial wave packet, both decoherence and collective motion occurs, although the latter typically dominates for a sufficiently dense gas. We derive explicit eigenfunctions for both collective and non-collective modes. If the angular mode distribution of electron-lepton number crosses between positive and negative values, two non-collective modes can merge to become a tachyonic collective mode. We explicitly calculate the interaction strength for this critical point. As a corollary we find that a single crossing always leads to a tachyonic instability. For an even number of crossings, no instability needs to occur.

Consequences of μ−τ reflection symmetry for 3+1 neutrino mixing

We investigate the consequences of $\mu-\tau$ reflection symmetry in presence of a light sterile neutrino for the $3+1$ neutrino mixing scheme. We discuss the implications of total $\mu-\tau$ reflection symmetry as well partial $\mu-\tau$ reflection symmetry. For the total $\mu-\tau$ reflection symmetry we find values of $\theta_{23}$ and $\delta$ remains confined near $\pi/4$ and $\pm \pi/2$ respectively. The current allowed region for $\theta_{23}$ and $\delta$ in case of inverted hierarchy lies outside the area preferred by the total $\mu-\tau$ reflection symmetry. However, interesting predictions on the neutrino mixing angles and Dirac CP violating phases are obtained considering partial $\mu-\tau$ reflection symmetry. We obtain predictive correlations between the neutrino mixing angle $\theta_{23}$ and Dirac CP phase $\delta$ and study the testability of these correlations at the future long baseline experiment DUNE. We find that while the imposition of $\mu-\tau$ reflection symmetry in the first column admit both normal and inverted neutrino mass hierarchy, demanding $\mu-\tau$ reflection symmetry for the second column excludes the inverted hierarchy. Interestingly, the sterile mixing angle $\theta_{34}$ gets tightly constrained considering the $\mu-\tau$ reflection symmetry in the fourth column. We also study consequences of $\mu-\tau$ reflection symmetry for the Majorana phases and neutrinoless double beta decay.

Modular S4 models of lepton masses and mixing

We investigate models of charged lepton and neutrino masses and lepton mixing based on broken modular symmetry. The matter fields in these models are assumed to transform in irreducible representations of the finite modular group Γ4 ≃ S4. We analyse the minimal scenario in which the only source of symmetry breaking is the vacuum expectation value of the modulus field. In this scenario there is no need to introduce flavon fields. Using the basis for the lowest weight modular forms found earlier, we build minimal phenomenologically viable models in which the neutrino masses are generated via the type I seesaw mechanism. While successfully accommodating charged lepton masses, neutrino mixing angles and mass-squared differences, these models predict the values of the lightest neutrino mass (i.e., the absolute neutrino mass scale), of the Dirac and Majorana CP violation (CPV) phases, as well as specific correlations between the values of the atmospheric neutrino mixing parameter sin2θ23 and i) the Dirac CPV phase δ, ii) the sum of the neutrino masses, and iii) the effective Majorana mass in neutrinoless double beta decay. We consider also the case of residual symmetries ℤ3ST and ℤ2S respectively in the charged lepton and neutrino sectors, corresponding to specific vacuum expectation values of the modulus.

Recent Result from RENO

The Reactor Experiment for Neutrino Oscillation (RENO) started data-taking from August, 2011 and has measured the smallest neutrino mixing angle θ13 by observing the disappearance of reactor antineutrinos. Antineutrinos from the six reactors at Hanbit Nuclear Power Plant in Korea are detected and compared by the two identical detectors located in the near and far distances from the reactor array center. We present recent results on precisely measured sin22θ13 value and based on spectral analysis using the 500 days of data sample, which are taken from August, 2011 to Jan, 2013.

CP Properties of Leptons within the Mirror Mechanism

Formation of quark and lepton mass matrices through intermediate states of heavy mirror fermions is capable of reproducing main qualitative properties of weak mixing matrices (CKM and PMNS matrices). The reproduction includes the hierarchy of CKM matrix elements, a general form of the PMNS matrix, involving the smallness of the neutrino mixing angle \theta_{13}, and leads to very small neutrino masses. For leptons, these properties appear only for the Dirac nature of SM neutrino and its inverse spectrum. In such a lepton system, not only do spontaneous mirror symmetry violation and the observed mass hierarchy of charged leptons (e,\mu,\tau) govern the structure of the PMNS matrix but also permit assessment of its allowed complexity, that is, the CP properties of leptons. The PMNS matrix then contains no Majorana phases and its Dirac phase \delta_{CP} corresponds to |\sin\delta_{CP}|, which is significantly smaller than unity.

New mixing schemes for (3+1) neutrinos

We propose new mixing schemes for (3+1) neutrinos which describe mixing among active-active and active-sterile neutrinos. The mixing matrix in these mixing schemes can be factored into a zeroth order flavor symmetric part and another part representing small perturbations needed for generating non-zero Ue3, nonmaximal θ23, CP violation and active-sterile mixing. We find interesting correlations amongst various neutrino mixing angles and, also, calculate the parameter space for various parameters.

Recent results from reactor antineutrino experiments

The smallest neutrino mixing angle \theta_{13}θ13 has been successfully measured by the disappearance of reactor antineutrinos at RENO, Daya Bay, and Double Chooz. The oscillation frequency is also measured based on energy and baseline dependent disappearance probability of reactor antineutrinos. Recent results find a variation in the observed reactor antineutrino flux as a function of the reactor fuel evolution. We report more precisely measured values of \theta_{13}θ13 and \Delta m_{ee}^2Δmee2 and results on the evolution of observed reactor antineutrino yield and spectrum.

A systematic analysis of perturbations for hexagonal mixing matrix

We present a systematic analysis of perturbative Hexagonal (HG) mixing for describing recent global fit neutrino mixing data with normal and inverted hierarchy. The corrections to unperturbed mixing are parametrized in terms of small orthogonal rotations [Formula: see text] with modified PMNS matrix of the forms [Formula: see text]. Here, [Formula: see text] is rotation in [Formula: see text] sector and [Formula: see text] is unperturbed Hexagonal mixing matrix. The detailed numerical investigation of all possible cases is performed with scanning of parameter space using [Formula: see text] approach. We found that the perturbative schemes governed by single rotation are unable to fit the mixing angle data even at [Formula: see text] level. The mixing schemes which involve two rotation matrices only [Formula: see text] are successful in fitting all neutrino mixing angles within [Formula: see text] range for normal hierarchy (NH). However for inverted hierarchy (IH), only [Formula: see text] is most preferable as it can fit all mixing angles at [Formula: see text] level. The remaining perturbative cases are either excluded at [Formula: see text] level or successful in producing mixing angles only at [Formula: see text] level. To study the impact of phase parameter, we also looked into CP violating effects for single rotation case. The predicted value of [Formula: see text] lies in the range [Formula: see text] for [Formula: see text] and [Formula: see text] case with normal (inverted) hierarchy.

Sensitivity to sterile neutrino mixing using reactor antineutrinos

The reactor antineutrinos are used for the precise measurement of oscillation parameters in the 3-neutrino model, and also used to investigate active-sterile neutrino mixing sensitivity in the 3+1 neutrino framework. In the present work, we study the feasibility of sterile neutrino search with the indian scintillator matrix for reactor anti-neutrino (ISMRAN) experimental set-up using electron antineutrinos ({overline{nu }}_e) produced from reactor as a source. The so-called 3+1 scenario is considered for active-sterile neutrino mixing, which leads to projected exclusion curves in the sterile neutrino mass and mixing angle plane. The analysis is performed considering both the reactor and detector related parameters. It is found that, the ISMRAN set-up can observe the active-sterile neutrino mixing sensitivity for sin ^{2}2theta _{14} ge 0.064 and varDelta m^{2}_{41} = 1.0hbox {eV}^2 at 90% confidence level for an exposure of 1 ton-year by using neutrinos produced from the DHRUVA reactor with thermal power of 100 hbox {MW}_{{th}}. It is also observed that, there is a significant improvement of the active-sterile neutrino mixing parameter sin ^{2}2theta _{14} to sim 0.03 at the same varDelta m^{2}_{41} by putting the ISMRAN detector set-up at a distance of 20 m from the compact proto-type fast breeder reactor facility with thermal power of 1250 hbox {MW}_{{th}}.

Low-scale leptogenesis with three heavy neutrinos

Leptogenesis induced by the oscillations of GeV-scale neutrinos provides a minimal and testable explanation of the baryon asymmetry of the Universe. In this work we extend previous studies invoking only two heavy neutrinos to the case of three heavy neutrinos. We find qualitatively new behaviour as a result of lepton number violating oscillations and decays, strong flavour effects in the washout and a resonant enhancement due to matter effects. An approximate global B-overline{L} symmetry (representing the difference of baryon and a generalised lepton number) can protect the light neutrino masses from large radiative corrections, while simultaneously providing the ingredients for the resonant enhancement of the lepton asymmetry due to thermal contributions to the heavy neutrino dispersion relations. This mechanism is particularly efficient for large heavy neutrino mixing angles near the current experimental limits, a regime in which leptogenesis is not feasible in the minimal scenario with two heavy neutrinos. In this new parameter regime, low-scale leptogenesis is testable by the LHC and other existing experiments.

Spontaneous μ-τ Reflection Symmetry Breaking in Neutrino Phenomenology

The latest global analysis of neutrino oscillation data indicates that the normal neutrino mass ordering is favored over the inverted one at the 3 σ level. The best-fit values of the largest neutrino mixing angle θ 23 and the Dirac CP-violating phase δ are located in the higher octant and the third quadrant, respectively. We show that these experimental trends can be naturally explained by the μ - τ reflection symmetry breaking, triggered by the one-loop renormalization-group equations (RGEs) running from a superhigh energy scale down to the electroweak scale in the framework of the minimal supersymmetric standard model (MSSM). The complete parameter space is numerically explored for both the Majorana and Dirac cases, by allowing the smallest neutrino mass m 1 and the MSSM parameter tan β to vary within their reasonable ranges.