Radiative Generation of the LMA Solution from Small Solar Neutrino Mixing at the GUT Scale

We show that in see-saw models with small or even vanishing lepton mixing angle $\theta_{12}$, maximal $\theta_{23}$, zero $\theta_{13}$ and zero CP phases at the GUT scale, the currently favored LMA solution of the solar neutrino problem can be obtained in a rather natural way by Renormalization Group effects. We find that most of the running takes place in the energy ranges above and between the see-saw scales, unless the charged lepton Yukawa couplings are large, which would correspond to a large $\tan \beta$ in the Minimal Supersymmetric Standard Model (MSSM). The Renormalization Group evolution of the solar mixing angle $\theta_{12}$ is generically larger than the evolution of $\theta_{13}$ and $\theta_{23}$. A large enhancement occurs for an inverted mass hierarchy and for a regular mass hierarchy with $|m_2 - m_1| \ll |m_2 + m_1|$. We present numerical examples of the evolution of the lepton mixing angles in the Standard Model and the MSSM, in which the current best-fit values of the LMA mixing angles are produced with vanishing solar mixing angle $\theta_{12}$ at the GUT scale.Comment: 10 pages, 6 figures; reference added, minor changes in the text; results unchanged; final version to appear in JHE

Hybrid Textures of Neutrinos

We present numerical and comprehensive analyses of the sixty hybrid textures of neutrinos, which have an equality of matrix elements and one zero. These textures are possibly derived from the discrete symmetry. Only six textures among sixty ones are excluded by the present experimental data. Since there are many textures which give similar predictions, the textures are classified based on the numerical results. The neutrinoless double beta decay is also examined in these textures. Our results suggest that there remain still rich structures of the neutrino mass matrix in the phenomenological point of view.Comment: 19 pages, 9 figures; analytical discussions added, table and reference adde

Solar neutrino oscillations and indications of matter effects in the Sun

Assuming the current best-fit solutions to the solar neutrino problem at large mixing angle, we briefly illustrate how prospective data from the Sudbury Neutrino Observatory (SNO) and from the Kamioka Liquid scintillator Anti-Neutrino Detector (KamLAND) can increase our confidence in the occurrence of standard matter effects on active neutrino flavor oscillations in the Sun, which are starting to emerge from current data.Comment: Updated to include the first KamLAND data. One figure adde

Solar Neutrinos and the Principle of Equivalence

We study the proposed solution of the solar neutrino problem which requires a flavor nondiagonal coupling of neutrinos to gravity. We adopt a phenomenological point of view and investigate the consequences of the hypothesis that the neutrino weak interaction eigenstates are linear combinations of the gravitational eigenstates which have slightly different couplings to gravity, $f_1G$ and $f_2G$, $|f_1-f_2| << 1$, corresponding to a difference in red-shift between electron and muon neutrinos, $\Delta z/(1+z) \sim |f_1 - f_2|$. We perform a $\chi^2$ analysis of the latest available solar neutrino data and obtain the allowed regions in the space of the relevant parameters. The existing data rule out most of the parameter space which can be probed in solar neutrino experiments, allowing only $|f_1 - f_2| \sim 3 \times 10^{-14}$ for small values of the mixing angle ($2 \times 10^{-3} \le \sin^2(2\theta_G) \le 10^{-2}$) and $10^{-16} \stackrel{<}{\sim} |f_1 - f_2| \stackrel{<}{\sim}10^{-15}$ for large mixing ($0.6 \le \sin^2(2\theta_G) \le 0.9$). Measurements of the $^8{\rm B}$-neutrino energy spectrum in the SNO and Super-Kamiokande experiments will provide stronger constraints independent of all considerations related to solar models. We show that these measurements will be able to exclude part of the allowed region as well as to distinguish between conventional oscillations and oscillations due to the violation of the equivalence principle.Comment: 20 pages + 4 figures, IASSNS-AST 94/5

Three-Neutrino Mixing after the First Results from K2K and KamLAND

We analyze the impact of the data on long baseline \nu_\mu disappearance from the K2K experiment and reactor \bar\nu_e disappearance from the KamLAND experiment on the determination of the leptonic three-generation mixing parameters. Performing an up-to-date global analysis of solar, atmospheric, reactor and long baseline neutrino data in the context of three-neutrino oscillations, we determine the presently allowed ranges of masses and mixing and we consistently derive the allowed magnitude of the elements of the leptonic mixing matrix. We also quantify the maximum allowed contribution of \Delta m^2_{21} oscillations to CP-odd and CP-even observables at future long baseline experiments.Comment: Some typos correcte

Deviation of Neutrino Mixing from Bi-maximal

We have studied how observables of the neutrino mixing matrix can link up with the ones in the quark sector. The deviation from the bi-maximal flavor mixing is parameterized using a 3 x 3 unitary matrix. The neutrino mixings are investigated supposing this unitary matrix to be hierarchical like the quark mixing matrix. We obtain the remarkable prediction |U_{e3}| >= 0.03 from the experimentally allowed range tan^2 theta_{sol} = 0.24 ~ 0.89. The CP violation in neutrino oscillations is expected to be very small.Comment: Some references are adde

The Oscillation Probability of GeV Solar Neutrinos of All Active Species

In this paper, I address the oscillation probability of O(GeV) neutrinos of all active flavours produced inside the Sun and detected at the Earth. Flavours other than electron-type neutrinos may be produced, for example, by the annihilation of WIMPs which may be trapped inside the Sun. In the GeV energy regime, matter effects are important both for the ``1-3'' system and the ``1-2'' system, and for different neutrino mass hierarchies. A numerical scan of the multidimensional three-flavour parameter space is performed, ``inspired'' by the current experimental situation. One important result is that, in the three-flavour oscillation case, P{alpha,beta} is different from P{beta,alpha} for a significant portion of the parameter space, even if there is no CP-violating phase in the MNS matrix. Furthermore, P{mu,mu} has a significantly different behaviour from P{tau,tau}, which may affect expectations for the number of events detected at large neutrino telescopes.Comment: 38 pages, 10 figure

Can the Zee Model Explain the Observed Neutrino Data?

The eigenvalues and mixing angles in the Zee model are investigated parameter-independently. When we require |\Delta m^2_{12}/\Delta m^2_{23}| \ll 1 in order to understand the solar and atmospheric data simultaneously, the only solution is one which gives bi-maximal mixing. It is pointed out that the observed values \sin^2 2\theta_{solar} \simeq 0.66 in the MSW LMA solution cannot be explained within the framework of the Zee model, because we derive a severe constraint on the value of \sin^2 2 \theta_{solar}, \sin^2 2 \theta_{solar} \geq 1 -(1/16)(\Delta m^2_{solar}/\Delta m^2_{atm})^2.Comment: Latex file, 10 pages, 1 figure, explanations and references added, typos corrected, to be published in Phys.Rev.

Solar neutrino oscillation parameters after first KamLAND results

We analyze the energy spectrum of reactor neutrino events recently observed in the Kamioka Liquid scintillator Anti-Neutrino Detector (KamLAND) and combine them with solar and terrestrial neutrino data, in the context of two- and three-family active neutrino oscillations. In the 2-neutrino case, we find that the solution to the solar neutrino problem at large mixing angle (LMA) is basically split into two sub-regions, that we denote as LMA-I and LMA-II. The LMA-I solution, characterized by lower values of the squared neutrino mass gap, is favored by the global data fit. This picture is not significantly modified in the 3-neutrino mixing case. A brief discussion is given about the discrimination of the LMA-I and LMA-II solutions with future KamLAND data. In both the 2- and 3-neutrino cases, we present a detailed analysis of the post-KamLAND bounds on the oscillation parameters.Comment: Revised version. Two figures adde

The Mars Science Laboratory record of optical depth measurements via solar imaging

Acknowledgments We are grateful to the teams that developed, landed, and operated Curiosity on Mars, allowing for the present study. The research was conducted partly at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004). MTL was supported via sub-contract 18-1187 from Malin Space Science Systems, Inc. SDG was supported by the MSL Participating Scientist program. JMB was supported by MSL Participating Scientist Grant 80NSSC22K0657. AV-R was supported by the Comunidad de Madrid Project S2018/NMT-4291 (TEC2SPACE-CM). M-PZ was supported by grant PID2019-104205GB-C21 funded by MCIN/AEI/10.13039/501100011033. JM-T was supported by UK Space Agency projects ST/W00190X/1 and ST/V00610X/1.Peer reviewedPostprin