Large Mixing Angle MSW Solution Research Articles

Erratum: Solar neutrino masses and mixing from bilinearR-parity broken supersymmetry: Analytical versus numerical results [Phys. Rev. D68, 013009 (2003)

We give an analytical calculation of solar neutrino masses and mixing at one-loop order within bilinear R-parity breaking supersymmetry, and compare our results to the exact numerical calculation. Our method is based on a systematic perturbative expansion of R-parity violating vertices to leading order. We find in general quite good agreement between approximate and full numerical calculation, but the approximate expressions are much simpler to implement. Our formalism works especially well for the case of the large mixing angle MSW solution (LMA-MSW), now strongly favoured by the recent KamLAND reactor neutrino data.

Escape from washing out of baryon number in a two-zero-texture general Zee model compatible with the large mixing angle MSW solution

We propose a two-zero-texture general Zee model, compatible with the large mixing angle Mikheyev-Smirnov-Wolfenstein solution. The washing out of the baryon number does not occur in this model for an adequate parameter range. We check the consistency of a model with the constraints coming from flavor changing neutral current processes, the recent cosmic microwave background observation, and the Z-burst scenario.

Inverted hierarchical model of neutrino masses revisited

In this Letter we highlight the inherent problems associated with the inverted hierarchical model of neutrinos with only three generations and then suggest possible solutions within the MSSM. We discuss the new parametrization of the solar mixing angle which can identify the light side and dark side of the data. We then argue whether the inverted hierarchical neutrino mass matrix can explain the large mixing angle (LMA) MSW solution of the solar neutrino anomaly in the presence of an appropriate texture of charged lepton mass matrix. In a model independent way we explore such specific form of the charged lepton mass matrix having a special structure in 1–2 block. The contribution to the solar mass splitting arising out of radiative corrections in MSSM, is calculated, thus making the model stable under radiative corrections.

Recent results of the Sudbury Neutrino Observatory

The Sudbury Neutrino Observatory (SNO) employs one kilotonne of ultra-pure D 2O to measure the flux of 8B neutrinos from the Sun through charged current (CC), neutral current (NC) and elastic scattering (ES) reactions. Based on data from “Phase P” of the experiment the non- ν e component of the solar neutrino flux is found to be different from zero at the 5.3σ level, providing strong evidence for solar ν e flavour transformation into active species. Global analyses of SNO data along with other solar neutrino experimental data, favour the large mixing angle (LMA) MSW solution at the 99% confidence level compared to other oscillation solutions. Future measurements of the SNO experiment are also discussed.

Determining the oscillation parameters by solar neutrinos and KamLAND

The neutrino oscillation experiment KamLAND has provided us with the first evidence for ν̄e disappearance, coming from nuclear reactors. We have combined their data with all solar neutrino data, assuming two flavor neutrino mixing, and obtained allowed parameter regions which are compatible with the so-called large mixing angle MSW solution to the solar neutrino problem. The allowed regions in the plane of mixing angle and mass squared difference are now split into two islands at 99% C.L. We have speculated how these two islands can be distinguished in the near future. We have shown that a 50% reduction of the error on SNO neutral-current measurement can be important in establishing in each of these islands the true values of these parameters lie. We also have simulated KamLAND positron energy spectrum after 1 year of data taking, assuming the current best fitted values of the oscillation parameters, combined it the with current solar neutrino data and showed how these two split islands can be modified.

Neutrino oscillation results from the Sudbury Neutrino Observatory

The Sudbury Neutrino Observatory (SNO) has determined the flavor content of the 8B solar neutrino flux by measuring the rates of charged current and neutral neutrino interactions on deuterium. These results directly demonstrate neutrino flavor transformation at greater than 5σ significance. The total flux of 8B neutrinos is found to be in good agreement with solar model predictions. Measurements of the day and night neutrino energy spectra probe models of neutrino oscillation. A global fit of SNO data and results from other solar neutrino experiments to neutrino oscillation models strongly favors the Large Mixing Angle (LMA) MSW solution.

The solar neutrino problem after the first results from KamLAND

The first results from the KamLAND experiment have provided confirmational evidence for the Large Mixing Angle (LMA) MSW solution to the solar neutrino problem. We do a global analysis of solar and the recently announced KamLAND data (both rate and spectrum) and investigate its effect on the allowed region in the $\Delta m^2-\tan^2\theta$ plane. The best-fit from a combined analysis which uses the KamLAND rate plus global solar data comes at $\Delta m^2 = 6.06 \times 10^{-5}$ eV $^2$ and $\tan^2\theta=0.42$, very close to the global solar best-fit, leaving a large allowed region within the global solar LMA contour. The inclusion of the KamLAND spectral data in the global fit gives a best-fit $\Delta m^2 = 7.15 \times 10^{-5}$ eV $^2$ and $\tan^2\theta=0.42$ and constrains the allowed areas within LMA, leaving essentially two allowed zones. Maximal mixing though allowed by the KamLAND data alone is disfavored by the global solar data and remains disallowed at about $3\sigma$. The LOW solution is now ruled out at about 5$\sigma$ w.r.t. the LMA solution.

Neutrino masses in astroparticle physics

The case for small neutrino mass differences from atmospheric and solar neutrino oscillation experiments has become compelling, but leaves the overall neutrino mass scale m ν undetermined. The most restrictive limit of m ν<0.8 eV arises from the 2dF galaxy redshift survey in conjunction with the standard theory of cosmological structure formation. A relation between the hot dark matter fraction and m ν depends on the cosmic number density n ν of neutrinos. If solar neutrino oscillations indeed correspond to the favored large mixing angle MSW solution, then big-bang nucleosynthesis gives us a restrictive limit on all neutrino chemical potentials, removing the previous uncertainty of n ν . Therefore, a possible future measurement of m ν will directly establish the cosmic neutrino mass fraction Ω ν . Cosmological neutrinos with sub-eV masses can play an interesting role for producing the highest-energy cosmic rays ( Z-burst scenario). Sub-eV masses also relate naturally to leptogenesis scenarios of the cosmic baryon asymmetry. Unfortunately, the time-of-flight dispersion of a galactic or local-group supernova neutrino burst is not sensitive in the sub-eV range.

Constructing the large mixing angle MNS matrix in see-saw models with right-handed neutrino dominance

Recent SNO results strongly favour the large mixing angle (LMA) MSW solar solution. We argue that there are only two technically natural low energy neutrino mass matrix structures consistent with the LMA MSW solution, corresponding to either a hierarchy or an inverted hierarchy with pseudo-Dirac neutrinos. We first present a model-independent analysis in which we diagonalise each of these two mass matrix structures to leading order in $\theta_{13}$ and extract the neutrino masses, mixing angles and phases. In this analysis we express the MNS matrix to leading order in the small angle $\theta_{13}$ including the neutrino {\em and} charged lepton mixing angles and phases, the latter playing a crucial r\^{o}le for allowing the inverted hierarchy case to be consistent with the LMA MSW solution. We then consider the see-saw mechanism with right-handed neutrino dominance and show how the successful neutrino mass matrix structures may be constructed with no tuning and with small radiative corrections, leading to a full, partial or inverted neutrino mass hierarchy. In each case we derive approximate analytic relations between the input see-saw parameters and the resulting neutrino masses, mixing angles and phases, which will provide a useful guide for unified model building. For the hierarchical cases the LMA MSW solution gives a soft lower bound $|U_{e3}|\simgt 0.1$, just below the current CHOOZ limit. Both hierarchical and inverted hierarchical cases predict small $\beta \beta_{0\nu}$ with $|m_{ee}|\sim 0.01$ eV within the sensitivity of future proposals such as GENIUS. Successful leptogenesis is possible if the dominant right-handed neutrino is the heaviest one, but the leptogenesis phase is unrelated to the MNS phases.

Majorana neutrinos in a warped 5D standard model

We consider neutrino oscillations and neutrinoless double beta decay in a five-dimensional standard model with warped geometry. Although the see-saw mechanism in its simplest form cannot be implemented because of the warped geometry, the bulk standard model neutrinos can acquire the desired (Majorana) masses from dimension five interactions. We discuss how large mixings can arise, why the large mixing angle MSW solution for solar neutrinos is favored, and provide estimates for the mixing angle Ue3. Implications for neutrinoless double beta decay are also discussed.

The HLMA project: determination of high Δ m2 LMA mixing parameters and constraint on | Ue3| with a new reactor neutrino experiment

In the forthcoming months, the KamLAND experiment will probe the parameter space of the solar large mixing angle MSW solution as the origin of the solar neutrino deficit with ν ̄ e ’s from distant nuclear reactors. If however the solution realized in nature is such that Δ m 2 sol≳2×10 −4 eV 2 (thereafter named the HLMA region), KamLAND will only observe a rate suppression but no spectral distortion and hence it will not have the optimal sensitivity to measure the mixing parameters. In this case, we propose a new medium baseline reactor experiment located at Heilbronn (Germany) to pin down the precise value of the solar mixing parameters. In this paper, we present the Heilbronn detector site, we calculate the ν ̄ e interaction rate and the positron spectrum expected from the surrounding nuclear power plants. We also discuss the sensitivity of such an experiment to | U e3| in both normal and inverted neutrino mass hierarchy scenarios. We then outline the detector design, estimate background signals induced by natural radioactivity as well as by in situ cosmic ray muon interaction, and discuss a strategy to detect the anti-neutrino signal ‘free of background’.

Constraints on | Ue3 | 2 from a three-neutrino oscillation analysis of the CHOOZ data

Results of a new analysis of the CHOOZ data, performed in the framework of three-neutrino mixing, are presented. Both the cases of normal and inverted neutrino mass hierarchy are considered. The parameters characterizing the solar neutrino oscillations, Δm 2 ⊙ and tan 2 θ ⊙, are assumed to lie in the region of the large mixing angle (LMA) MSW solution of the solar neutrino problem, which is favored by the current solar neutrino data. At Δm 2 ⊙≲10 −4 eV 2 the new CHOOZ exclusion curve in the Δm 2 31–| U e3 | 2 plane practically coincides with the exclusion curve obtained in the two-neutrino mixing analysis. For Δm 2 ⊙≳2×10 −4 eV 2, the constraints of the CHOOZ data on | U e3 | 2 are more stringent. For, e.g., sin 2 θ ⊙=0.50 and Δm 2 ⊙=6×10 −4 eV 2, and at Δm 2 31=2.5×10 −3 eV 2 (the Super-Kamiokande best fit-point) we find that (at 90% C.L.) | U e3 | 2<1.7×10 −2, which is by more than a factor of 2 smaller than the upper bound obtained in the original two-neutrino mixing analysis of the CHOOZ data (| U e3 | 2<3.7×10 −2).

Cosmological bounds on neutrino degeneracy improved by flavor oscillations

We study three-flavor neutrino oscillations in the early universe in the presence of neutrino chemical potentials. We take into account all effects from the background medium, i.e., collisional damping, the refractive effects from charged leptons, and in particular neutrino self-interactions that synchronize the neutrino oscillations. We find that effective flavor equilibrium between all active neutrino species is established well before the big-bang nucleosynthesis (BBN) epoch if the neutrino oscillation parameters are in the range indicated by the atmospheric neutrino data and by the large mixing angle (LMA) MSW solution of the solar neutrino problem. For the other solutions of the solar neutrino problem, partial flavor equilibrium may be achieved if the angle θ 13 is close to the experimental limit tan 2 θ 13≲0.065. In the LMA case, the BBN limit on the ν e degeneracy parameter, | ξ ν |≲0.07, now applies to all flavors. Therefore, a putative extra cosmic radiation contribution from degenerate neutrinos is limited to such low values that it is neither observable in the large-scale structure of the universe nor in the anisotropies of the cosmic microwave background radiation. Existing limits and possible future measurements, for example in KATRIN, of the absolute neutrino mass scale will provide unambiguous information on the cosmic neutrino mass density, essentially free of the uncertainty of the neutrino chemical potentials.

Family replicated gauge groups and large mixing angle solar neutrino solution

We present a modification of our previous family replicated gauge group model, which now generates the Large Mixing Angle MSW solution rather than the experimentally disfavoured Small Mixing Angle MSW solution to the solar neutrino oscillation problem. The model is based on each family of quarks and leptons having its own set of gauge fields, each containing a replica of the Standard Model gauge fields plus a ( B− L)-coupled gauge field. By a careful choice of the Higgs field gauge quantum numbers, we avoid our previous prediction that the solar neutrino mixing angle is equal order of magnitudewise to the Cabibbo angle, replacing it and the well-known Fritzsch relation with the relation θ c∼(θ ⊙) −1/3 (m d/m s) 2/3 . At the same time we retain a phenomenologically successful structure for the charged quark and lepton mass matrices. A fit of all the seventeen quark–lepton mass and mixing angle observables, using just six new Higgs field vacuum expectation values, agrees with the experimental data within the theoretically expected uncertainty of about 64%, i.e., it fits perfectly order of magnitudewise.

Lepton flavor violating process in degenerate and inverse-hierarchical neutrino models

We have investigated the lepton flavor violation in the supersymmetric framework assuming the large mixing angle MSW solution with the quasi-degenerate and the inverse-hierarchical neutrino masses. In the case of the quasi-degenerate neutrinos, the predicted branching ratio BR$(\mu \to e \gamma)$ strongly depends on $m_\nu$ and $U_{e3}$. For $U_{e3}\simeq 0.05$ with $m_\nu \simeq 0.3 \eV$, the prediction is close to the present experimental upper bound if the right-handed Majorana neutrino masses are degenerate. On the other hand, the prediction is larger than the experimental upper bound for $U_{e3}\geq 0.05$ in the case of the inverse-hierarchical neutrino masses.

Solar Neutrino Oscillations with Large Mixing Angle MSW Solution in an Extended Zee Model(SUMMER INSTITUTE 2001, Session 2: Phenomenology)

Solar Neutrino Oscillations with Large Mixing Angle MSW Solution in an Extended Zee Model(SUMMER INSTITUTE 2001, Session 2: Phenomenology)

E6 Unification with Bi-Large Neutrino Mixing

A scenario of SO(10) grand unified theory (GUT) proposed by one of the authors is extended to E_6 unification. This gives realistic quark and lepton mass matrices. In neutrino sector, the model reproduces large mixing angle (LMA) MSW solution as well as large mixing angle for atmospheric neutrino anomaly. In this model, right-handed down quark and left-handed lepton of the first and second generation belong to a single multiplet 27. This causes natural suppression of flavor changing neutral current(FCNC).

Obtaining the large angle MSW solution to the solar neutrino problem in models

The large mixing angle (LMA) MSW solution to the solar neutrino problem seems favored by the data at the moment over the small mixing angle (SMA) MSW solution and the vacuum (VAC) solution. In this paper the various main types of models of neutrino masses and mixings are studied from the point of view of how naturally they can give the LMA solution. Special attention is given to a very simple type of “lopsided” SU(5) model.

The neutrino factory: machine and detectors

The main features of a neutrino factory using storedmuon beams are discussed. The accumulating evidence forneutrino oscillations mean that there is a strongmotivation for further studies of neutrino mixing withmore intense, accelerator-generated beams. In particular,the probability is increasing that the large mixing angleMSW solution is the explanation of the solar neutrinodeficit observed over many years. This indicates that CP-or T-violation in the lepton sector may be experimentallyaccessible if sufficiently intense beams can beconstructed, in order to serve detectors with baselinesof several thousand kilometres. The neutrino factory, withits intense neutrino beams of well known energy spectrum,flux and flavour composition, satisfies the requirements.

Mikheyev–Smirnov–Wolfenstein Effect on Neutrino Decay

It has early been pointed out by R S Raghavan et al. that in solar matter, conversion of the electron neutrino to a “heaver” flavor by the MSW effect can catalyze neutrino decay in the small mixing angle MSW solution. Since recent results on solar neutrinos provide hints that the large mixing angle MSW solution could be correct, we present a detailed study of the MSW effect with neutrino decay for both small and large mixing angles. The lower limit for the lifetime of 10 MeV neutrinos is estimated to be τ(10 MeV) ≳ 103 s.