Current Neutrino Oscillation Data Research Articles

Investigating texture six zero lepton mass matrices

Texture six zero Fritzsch like as well as non Fritzsch like hermitian lepton mass matrices (144 combinations in all) have been investigated for both Majorana and Dirac neutrinos for their compatibility with the current neutrino oscillation data, keeping in mind the hierarchy of neutrino masses. All the combinations considered here for Majorana neutrino masses are ruled out by the existing data in the case of inverted hierarchy and degenerate scenario. For Majorana neutrinos with normal hierarchy, only 16 combinations can accommodate the experimental data. Assuming neutrinos to be Dirac particles, normal hierarchy, inverted hierarchy as well as degenerate neutrinos are ruled out for all combinations of texture 6 zero hermitian mass matrices.

TEXTURE ZEROS FOR DIRAC NEUTRINOS AND CURRENT EXPERIMENTAL TESTS

The Daya Bay and RENO reactor neutrino experiments have revealed that the smallest neutrino mixing angle is in fact relatively large, i.e. θ13 ≈9°. Motivated by this exciting progress, we perform a systematic study of the neutrino mass matrix Mν with one or two texture zeros, in the assumption that neutrinos are Dirac particles. Among 15 possible patterns with two texture zeros, only three turn out to be favored by current neutrino oscillation data at the 3σ level. Although all the six patterns with one texture zero are compatible with the experimental data at the 3σ level, the parameter space of each pattern is strictly constrained. Phenomenological implications of Mν on the leptonic CP violation and neutrino mass spectrum are explored, and the stability of texture zeros against the radiative corrections is also discussed.

Nonzero |U e3| from charged lepton corrections and the atmospheric neutrino mixing angle

After the successful determination of the reactor neutrino mixing angle \theta_13 ~ 0.16 \neq 0, a new feature suggested by the current neutrino oscillation data is a sizeable deviation of the atmospheric neutrino mixing angle \theta_23 from \pi/4. Using the fact that the neutrino mixing matrix U = U_e^\dagger U_\nu, where U_e and U_\nu result from the diagonalisation of the charged lepton and neutrino mass matrices, and assuming that U_\nu has a i) bimaximal (BM), ii) tri-bimaximal (TBM) form, or else iii) corresponds to the conservation of the lepton charge L' = L_e - L_\mu - L_\tau (LC), we investigate quantitatively what are the minimal forms of U_e, in terms of angles and phases it contains, that can provide the requisite corrections to U_\nu so that \theta_13, \theta_23 and the solar neutrino mixing angle \theta_12 have values compatible with the current data. Two possible orderings of the 12 and the 23 rotations in U_e, "standard" and "inverse", are considered. The results we obtain depend strongly on the type of ordering. In the case of "standard" ordering, in particular, the Dirac CP violation phase \delta, present in U, is predicted to have a value in a narrow interval around i) \delta ~ \pi in the BM (or LC) case, ii) \delta ~ 3\pi/2 or \pi/2 in the TBM case, the CP conserving values \delta = 0, \pi, 2\pi being excluded in the TBM case at more than 4\sigma. In the addendum we discuss the implications of the latest 2013 data.

A further study of [formula omitted] symmetry breaking at neutrino telescopes after the Daya Bay and RENO measurements of [formula omitted

Current neutrino oscillation data indicate that θ13 is not strongly suppressed and θ23 might have an appreciable deviation from π/4, implying that the 3×3 neutrino mixing matrix V does not have an exact μ–τ permutation symmetry. We make a further study of the effect of μ–τ symmetry breaking on the democratic flavor distribution of ultrahigh-energy (UHE) cosmic neutrinos at a neutrino telescope, and find that it is characterized by |Vμi|2−|Vτi|2 which would vanish if either θ23=π/4 and θ13=0 or θ23=π/4 and δ=±π/2 held. We observe that the second-order μ–τ symmetry breaking term Δ¯ may be numerically comparable with or even larger than the first-order term Δ in the flux ratios ϕeT:ϕμT:ϕτT≃(1−2Δ):(1+Δ+Δ¯):(1+Δ−Δ¯), if sin(θ23−π/4) and cosδ have the same sign. The detection of the UHE ν¯e flux via the Glashow-resonance channel ν¯ee→W−→anything is also discussed by taking account of the first- and second-order μ–τ symmetry breaking effects.

Studies of a three-stage dark matter and neutrino observatory based on multi-ton combinations of liquid xenon and liquid argon detectors

We study a three stage dark matter and neutrino observatory based on multi-ton two-phase liquid Xe and Ar detectors with sufficiently low backgrounds to be sensitive to WIMP dark matter interaction cross sections down to 10-47cm2, and to provide both identification and two independent measurements of the WIMP mass through the use of the two target elements in a 5:1 mass ratio, giving an expected similarity of event numbers. The same detection systems will also allow measurement of the pp solar neutrino spectrum, the neutrino flux and temperature from a Galactic supernova, and neutrinoless double beta decay of 136Xe to the lifetime level of 1027–1028y corresponding to the Majorana mass predicted from current neutrino oscillation data. The proposed scheme would be operated in three Generic stages G2, G3, G4, beginning with fiducial masses 1-ton Xe+5-ton Ar (G2), progressing to 10-ton Xe+50-ton Ar (G3) then, dependent on results and performance of the latter, expandable to 100-ton Xe+500-ton Ar (G4). This method of scale-up offers the advantage of utilizing the Ar vessel and ancillary systems of one stage for the Xe detector of the succeeding stage, requiring only one new detector vessel at each stage. Simulations show the feasibility of reducing or rejecting all external and internal background levels to a level <1 events per year for each succeeding mass level, by utilizing an increasing outer thickness of target material as self-shielding. The system would, with increasing mass scale, become increasingly sensitive to annual signal modulation, the agreement of Xe and Ar results confirming the Galactic origin of the signal. Dark matter sensitivities for spin-dependent and inelastic interactions are also included, and we conclude with a discussion of possible further gains from the use of Xe/Ar mixtures.

Unified triminimal parametrizations of quark and lepton mixing matrices

We present a detailed study on triminimal parametrizations of quark and lepton mixing matrices with different basis matrices. We start with a general discussion on the triminimal expansion of the mixing matrix and on possible unified quark and lepton parametrization using quark-lepton complementarity. We then consider several interesting basis matrices and compare the triminimal parametrizations with the Wolfenstein-like parametrizations. The usual Wolfenstein parametrization for quark mixing is a triminimal expansion around the unit matrix as the basis. The corresponding quark-lepton complementarity lepton mixing matrix is a triminimal expansion around the bimaximal basis. Current neutrino oscillation data show that the lepton mixing matrix is very well represented by the tribimaximal mixing. It is natural to take it as an expanding basis. The corresponding zeroth order basis for quark mixing in this case makes the triminimal expansion converge much faster than the usual Wolfenstein parametrization. The triminimal expansion based on tribimaximal mixing can be converted to the Wolfenstein-like parametrizations discussed in the literature. We thus have a unified description between different kinds of parametrizations for quark and lepton sectors: the standard parametrizations, the Wolfenstein-like parametrizations, and the triminimal parametrizations.

X-ray photons from late-decaying majoron dark matter

An attractive way to generate neutrino masses as required to account for current neutrinooscillation data involves the spontaneous breaking of lepton number. The resultingmajoron may pick up a mass due to gravity. If its mass lies in the kilovolt scale,the majoron can play the role of late-decaying dark matter (LDDM), decayingmainly to neutrinos. In general the majoron has also a sub-dominant decay to twophotons leading to a mono-energetic emission line which can be used as a test of theLDDM scenario. We compare expected photon emission rates with observations inorder to obtain model-independent restrictions on the relevant parameters. Wealso illustrate the resulting sensitivities within an explicit seesaw realization,where the majoron couples to photons due to the presence of a Higgs triplet.

Probing bilinear R-parity violating supergravity at the LHC

We study the collider phenomenology of bilinear R-parity violating supergravity, the simplest effective model for supersymmetric neutrino masses accounting for the current neutrino oscillation data. At the CERN Large Hadron Collider the center-of-mass energy will be high enough to probe directly these models through the search for the superpartners of the Standard Model (SM) particles. We analyze the impact of R-parity violation on the canonical supersymmetry searches—that is, we examine how the decay of the lightest supersymmetric particle (LSP) via bilinear R-parity violating interactions degrades the average expected missing momentum of the reactions and show how this diminishes the reach in the usual channels for supersymmetry searches. However, the R-parity violating interactions lead to an enhancement of the final states containing isolated same-sign di-leptons and trileptons, compensating the reach loss in the fully inclusive channel. We show how the searches for displaced vertices associated to LSP decay substantially increase the coverage in supergravity parameter space, giving the corresponding reaches for two reference luminosities of 10 and 100 fb−1 and compare with those of the R-parity conserving minimal supergravity model.

Lepton number violating mSUGRA and neutrino masses

We perform a quantitative study of neutrino phenomenology in the framework of minimal supergravity (mSUGRA) with grand unified theory (GUT)-scale tri-linear lepton number violation. We show that only two non-zero GUT scale lepton number violating parameters and three charged lepton mixing angles are sufficient to account for current neutrino oscillation data. This allows collider studies to be performed in a manageable parameter space. We discuss some phenomenological consequences of the models, including tuning issues.

Leptoquarks: Neutrino masses and related accelerator signals

Leptoquark-Higgs interactions induce mixing between leptoquark (LQ) states with different chiralities once the electroweak symmetry is broken. In such LQ models Majorana neutrino masses are generated at 1-loop order. Here we calculate the neutrino mass matrix and explore the constraints on the parameter space enforced by the assumption that LQ-loops explain current neutrino oscillation data. LQs will be produced at the CERN LHC, if their masses are at or below the TeV scale. Since the fermionic decays of LQs are governed by the same Yukawa couplings, which are responsible for the nontrivial neutrino mass matrix, several decay branching ratios of LQ states can be predicted from measured neutrino data. Especially interesting is that large lepton flavor violating rates in muon and tau final states are expected. In addition, the model predicts that, if kinematically possible, heavier LQs decay into lighter ones plus either a standard model Higgs boson or a ${Z}^{0}/{W}^{\ifmmode\pm\else\textpm\fi{}}$ gauge boson. Thus, experiments at the LHC might be able to exclude the LQ mechanism as an explanation of neutrino data.

Fermion masses, leptogenesis, and supersymmetric SO(10) unification

Current neutrino oscillation data indicate the existence of two large lepton mixing angles, while Kobayashi-Maskawa matrix elements are all small. Here we show how supersymmetric SO(10) with extra chiral singlets can easily reconcile large lepton mixing angles with small quark mixing angles within the framework of the successful Fritzsch ansatz. Moreover, we show how this is fully consistent with the thermal leptogenesis scenario, avoiding the so-called gravitino problem. A sizable asymmetry can be generated at scales as low as possible within the leptogenesis mechanism. We present our results in terms of the leptonic $CP$ violation parameter that characterizes neutrino oscillations.

A [formula omitted] texture for neutrino oscillations and leptogenesis

In an economical system with only two heavy right-handed neutrinos, we postulate a new texture for 3×2 Dirac mass matrix mD. This model implies one massless light neutrino and thus displays only two patterns of mass spectrum for light neutrinos, namely hierarchical or inverse-hierarchical. Both the cases can correctly reproduce all the current neutrino oscillation data with a unique prediction mνeνe=Δmsolar23 and Δmatm2 for the hierarchical and the inverse-hierarchical cases, respectively, which can be tested in next generation neutrino-less double beta decay experiments. Introducing a single physical CP phase in mD, we examine baryon asymmetry through leptogenesis. Interestingly, through the CP phase there are correlations between the amount of baryon asymmetry and neutrino oscillation parameters. We find that for a fixed CP phase, the hierarchical case also succeeds in generating the observed baryon asymmetry in our universe, plus a non-vanishing Ue3 which is accessible in future baseline neutrino oscillation experiments.

Neutrino mixing and leptogenesis in type-II seesaw scenarios with left–right symmetry

We propose two type-II seesaw scenarios for the neutrino mass matrix in the left–right symmetric model, in which the Higgs triplet Yukawa coupling matrix takes the appealing Friedberg–Lee texture. We show that the nearly tri-bimaximal neutrino mixing pattern, which is especially favored by current neutrino oscillation data, can be obtained from both scenarios. We also show that the cosmological baryon number asymmetry can naturally be interpreted in these two scenarios via the flavor-independent leptogenesis mechanism.

GENERALIZED FUKUGITA–TANIMOTO–YANAGIDA NEUTRINO MASS ANSATZ

We generalize the Fukugita–Tanimoto–Yanagida ansatz by allowing the masses of three heavy right-handed Majorana neutrinos, Mi (i = 1,2,3), to be partially non-degenerate and search for the parameter space which can be consistent with the current neutrino oscillation data, for three non-degenerate mass cases (A) M3 = M2 ≠ M1, (B) M2 = M1 ≠ M3 and (C) M1 = M3 ≠ M2. We also examine the effect of the deviation from the complete mass degeneracy in each case. Finally, we obtain the numerical constraints on three light neutrino masses, three neutrino mixing angles and three CP-violating phases, together with the predictions for the Jarlskog invariant of CP violation and the effective masses of the tritium beta decay and the neutrinoless double-beta decay.

Neutrino telescopes as a probe of broken μ- τ symmetry

The ultrahigh-energy (UHE) neutrinos produced from a distant astrophysical source must oscillate many times on the way to the Earth. Assuming the conventional UHE neutrino source with the flavor ratio ϕ e : ϕ μ : ϕ τ = 1 : 2 : 0 , I show that ϕ e D : ϕ μ D : ϕ τ D = ( 1 − 2 Δ ) : ( 1 + Δ ) : ( 1 + Δ ) holds at the detector of a km 3 -size neutrino telescope, where Δ signifies the effect of μ - τ symmetry breaking (i.e., θ 13 ≠ 0 and θ 23 ≠ π / 4 ). Current neutrino oscillation data yield − 0.1 ⩽ Δ ⩽ + 0.1 . I point out that it is also possible to probe Δ by detecting the ν ¯ e flux of E ν ¯ e ≈ 6.3 PeV via the Glashow resonance channel ν ¯ e e → W − → anything .

Cosmological Matter-Antimatter Asymmetry and Neutrino Oscillations

I conjecture that three light Majorana neutrinos and their right-handed counterparts may have a universal geometric mass hierarchy. Incorporating this phenomenological conjecture with the Fritzsch texture of lepton mass matrices in a simple seesaw mechanism, I show that it is possible to simultaneously account for current neutrino oscillation data and the cosmological baryon number asymmetry via leptogenesis.

NEUTRINO MASSES, LEPTON FLAVOR MIXING AND LEPTOGENESIS IN THE MINIMAL SEESAW MODEL

We present a review of neutrino phenomenology in the minimal seesaw model (MSM), an economical and intriguing extension of the Standard Model with only two heavy right-handed Majorana neutrinos. Given current neutrino oscillation data, the MSM can predict the neutrino mass spectrum and constrain the effective masses of the tritium beta decay and the neutrinoless double-beta decay. We outline five distinct schemes to parameterize the neutrino Yukawa-coupling matrix of the MSM. The lepton flavor mixing and baryogenesis via leptogenesis are investigated in some detail by taking account of possible texture zeros of the Dirac neutrino mass matrix. We derive an upper bound on the CP-violating asymmetry in the decay of the lighter right-handed Majorana neutrino. The effects of the renormalization-group evolution on the neutrino mixing parameters are analyzed, and the correlation between the CP-violating phenomena at low and high energies is highlighted. We show that the observed matter-antimatter asymmetry of the Universe can naturally be interpreted through the resonant leptogenesis mechanism at the TeV scale. The lepton-flavor-violating rare decays, such as μ→e+γ, are also discussed in the supersymmetric extension of the MSM.

On the Fukugita–Tanimoto–Yanagida ansatz with partially non-degenerate right-handed Majorana neutrinos

Taking three right-handed Majorana neutrino masses M i to be partially non-degenerate, we make a new analysis of the Fukugita–Tanimoto–Yanagida ansatz and confront it with current neutrino oscillation data. We determine the parameter space for cases (A) M 3 = M 2 ≠ M 1 , (B) M 2 = M 1 ≠ M 3 and (C) M 1 = M 3 ≠ M 2 , and examine their respective deviations from the original M 1 = M 2 = M 3 case. The numerical constraints on three light neutrino masses, three neutrino mixing angles and three CP-violating phases are also obtained, together with the predictions for the Jarlskog invariant of CP violation and the effective masses of the tritium beta decay and the neutrinoless double-beta decay.

Neutrino telescopes as a probe of brokenμ−τsymmetry

It is known that neutrino oscillations may map $\phi_e : \phi_\mu : \phi_\tau = 1 : 2 : 0$, the initial flavor ratios of ultrahigh-energy neutrino fluxes produced from a distant astrophysical source, into $\phi^D_e : \phi^D_\mu : \phi^D_\tau = 1 : 1 : 1$ at the detector of a neutrino telescope. We remark that this naive expectation is only valid in the $\mu$-$\tau$ symmetry limit, in which two neutrino mixing angles satisfy $\theta_{13} = 0$ and $\theta_{23} = \pi/4$. Allowing for the slight breaking of $\mu$-$\tau$ symmetry, we find $\phi^D_e : \phi^D_\mu : \phi^D_\tau = (1 -2 \Delta) : (1 +\Delta) : (1 +\Delta)$ with $\Delta$ characterizing the combined effect of $\theta_{13} \neq 0$ and $\theta_{23} \neq \pi/4$. Current neutrino oscillation data indicate $-0.1 \lesssim \Delta \lesssim +0.1$. We also look at the possibility to probe $\Delta$ by detecting the $\bar{\nu}_e$ flux of $E_{\bar{\nu}_e} \approx 6.3 {\rm PeV}$ via the Glashow resonance channel $\bar{\nu}_e e \to W^- \to anything$.

Probing neutrino masses with CMB lensing extraction

We evaluate the ability of future cosmic microwave background (CMB) experiments to measure the power spectrum of large scale structure using quadratic estimators of the weak lensing deflection field. We calculate the sensitivity of upcoming CMB experiments such as BICEP, QUaD, BRAIN, ClOVER and Planck to the nonzero total neutrino mass ${M}_{\ensuremath{\nu}}$ indicated by current neutrino oscillation data. We find that these experiments greatly benefit from lensing extraction techniques, improving their one-sigma sensitivity to ${M}_{\ensuremath{\nu}}$ by a factor of order four. The combination of data from Planck and the SAMPAN mini-satellite project would lead to $\ensuremath{\sigma}({M}_{\ensuremath{\nu}})\ensuremath{\sim}0.1$ eV, while a value as small as $\ensuremath{\sigma}({M}_{\ensuremath{\nu}})\ensuremath{\sim}0.035$ eV is within the reach of a space mission based on bolometers with a passively cooled 3--4 m aperture telescope, representative of the most ambitious projects currently under investigation. We show that our results are robust not only considering possible difficulties in subtracting astrophysical foregrounds from the primary CMB signal but also when the minimal cosmological model ($\ensuremath{\Lambda}$ Mixed Dark Matter) is generalized in order to include a possible scalar tilt running, a constant equation-of-state parameter for the dark energy and/or extra relativistic degrees of freedom.