Solar neutrino oscillation phenomenology

This article summarises the status of the solar neutrino oscillation phenomenology at the end of 2002 in the light of the SNO and KamLAND results. We first present the allowed areas obtained from global solar analysis and demonstrate the preference of the solar data towards the large-mixing-angle (LMA) MSW solution. A clear confirmation in favour of the LMA solution comes from the KamLAND reactor neutrino data. The KamLAND spectral data in conjunction with the global solar data further narrows down the allowed LMA region and splits it into two allowed zones a low Δm ² region (low-LMA) and high Δm ² region (high-LMA). We demonstrate through a projected analysis that with an exposure of 3 kton-year (kTy) KamLAND can remove this ambiguity.     

Solving Solar Neutrino Puzzle via LMA MSW Conversion

We analyze the existing solar neutrino experiment data and show the allowed regions. The result from SNO＇s salt phase itself restricts quite a lot the allowed region＇s area. Reactor neutrinos play an important role in determining oscillation parameters. KamLAND gives decisive conclusion on the solution to the solar neutrino puzzle, in particular, the spectral distortion in the 766.3 Ty KamLAND data gives another new improvement in the constraint of solar MSW-LMA solutions. We confirm that at 99.73% C.L. the high-LMA solution is excluded.     

Muon与Tau中微子的运动学有效质量及其不可探测性

利用最新的WMAP观测数据推导出电子、Muon和Tau中微子的运动学有效质量的一般上限:e2+μ2+τ2=m12+m22+m32<0.5eV2,或α<0.71eV(其中α=e,μ,τ)。考虑现有中微子振荡的实验数据,进一步得到e<0.24eV以及μ≈τ<0.24eV. 因此有效质量_μ和_τ太小而无法被探测.     

Bi-large Neutrino Mixing See-Saw Mass Matrix with Texture Zeros and Leptogenesis

We study constraints on neutrino properties for a class of bi-large mixing See-Saw mass matrices with texture zeros and with the related Dirac neutrino mass matrix to be proportional to a diagonal matrix of the form diag(ε,1,1). Texture zeros may occur in the light (class a) or in the heavy (class b) neutrino mass matrices. Each of these two classes has 5 different forms which can produce non-trivial three generation mixing with at least one texture zero. We find that two types of texture zero mass matrices in both class a and class b can be consistent with present data on neutrino masses and mixing. None of the neutrinos can have zero masses and the lightest of the light neutrinos has a mass larger than about 0.046 eV for class a and 0.0027 eV for class b. In these models although the CKM CP violating phase vanishes, the non-zero Majorana phases can exist and can play an important role in producing the observed baryon asymmetry in our universe through leptogenesis mechanism. The requirement of producing the observed baryon asymmetry can further distinguish different models and also restrict the See-Saw scale to be in the range of 10¹²～10¹⁵ GeV. We also discuss RG effects on V₁₃.     

Earthquake forecast via neutrino tomography

We discuss the possibility of forecasting earthquakes by means of (anti)neutrino tomography. An- tineutrinos emitted from reactors are used as a probe. As the antineutrinos traverse through a region prone to earthquakes, observable variations in the matter effect on the antineutrino oscillation would provide a tomog- raphy of the vicinity of the region. In this preliminary work, we adopt a simplified model for the geometrical profile and matter density in a fault zone. We calculate the survival probability of electron antineutrinos for cases without and with an anomalous accumulation of electrons which can be considered as a clear signal of the coming earthquake, at the geological region with a fault zone, and find that the variation may reach as much as 3% for ν<,e> emitted from a reactor. The case for a ν<,e> beam from a neutrino factory is also investigated, and it is noted that, because of the typically high energy associated with such neutrinos, the oscillation length is too large and the resultant variation is not practically observable. Our conclusion is that with the present reactor facilities and detection techniques, it is still a difficult task to make an earthquake forecast using such a scheme, though it seems to be possible from a theoretical point of view while ignoring some uncertainties. However, with the development of the geology, especially the knowledge about the fault zone, and with the improvement of the detection techniques, etc., there is hope that a medium-term earthquake forecast would be feasible.     

Bounds on neutrino mixing with exotic singlet neutrinos

We examine the effects of mixing induced non-diagonal light-heavy neutrino weak neutral currents on the amplitude for the process (with a=e, μ or τ). By imposing constraint that the amplitude should not exceed the perturbative unitarity limit at high energy , we obtain bounds on light-heavy neutrino mixing parameter sin² where is the mixing angle. In the case of one heavy neutrino (mass mξ) or mass degenerate heavy neutrinos, for Λ=1 TeV, no bound is obtained for mξ<0.50 TeV. However, sin² ≤3.8 × 10⁻⁶ for mξ=5 TeV and sin ≤6.0 × 10⁻⁸ for mξ=10 TeV. For Λ=∞, no constraint is obtained for mξ<0.99 TeV and sin² ≤3.8 × 10⁻² (for mξ=5 TeV) and sin² ≤9.6 × 10⁻³ (for mξ=10 TeV).     

Leptogenesis models and neutrino mass constraints

Through leptogenesis, baryogenesis could have the same origin as neutrino masses. We review the various ways of implementing the leptogenesis mechanism. Emphasis is put on the conditions which, in order that this mechanism works, need to be fulfilled by the neutrino masses as well as by the heavy state masses.     

Atmospheric neutrinos and discovery of neutrino oscillations

Neutrino oscillation was discovered through studies of neutrinos produced by cosmic-ray interactions in the atmosphere. These neutrinos are called atmospheric neutrinos. They are produced as decay products in hadronic showers resulting from collisions of cosmic rays with nuclei in the atmosphere. Electron-neutrinos and muon-neutrinos are produced mainly by the decay chain of charged pions to muons to electrons. Atmospheric neutrino experiments observed zenith-angle and energy dependent deficit of muon-neutrino events. Neutrino oscillations between muon-neutrinos and tau-neutrinos explain these data well. Neutrino oscillations imply that neutrinos have small but non-zero masses. The small neutrino masses have profound implications to our understanding of elementary particle physics and the Universe. This article discusses the experimental discovery of neutrino oscillations.     

Antineutrino science by KamLAND

KamLAND measured the $\bar{\nu }$_e’s flux from distant nuclear reactors, and found fewer events than expected from standard assumptions about $\bar{\nu }$_e propagation at the 99.998% confidence level (C.L.). The observed energy spectrum disagrees with the expected spectral shape at 99.6% C.L., and prefers the distortion from neutrino oscillation effects. A two-flavor oscillation analysis of the data from KamLAND and solar neutrino experiments with CPT invariance, yields Δm2=7.9−0.5+0.6×10−5 eV² and tan2θ=0.40−0.07+0.10. All solutions to the solar neutrino problem except for the large mixing angle (LMA) region are excluded. KamLAND succeeded in detecting geoneutrinos produced by the decays of ²³⁸U and ²³²Th within the Earth. The total observed number of 4.5 to 54.2, assuming a Th/U mass concentration ratio of 3.9 is consistent with 19 predicted by geophysical models. This detection allows better estimation of the abundances and distributions of radioactive elements in the Earth, and of the Earth’s overall heat budget.     

Detecting dark energy in long baseline neutrino oscillations

In this paper, we discuss a possibility of studying properties of dark energy in long baseline neutrino oscillation experiments. We consider two types of models of neutrino dark energy. For one type of models the scalar field is taken to be quintessence-like and for the other phantom-like. In these models the scalar fields couple to the neutrinos to give rise to spatially varying neutrino masses. We will show that the two types of models predict different behaviors of the spatial variation of the neutrino masses inside the Earth and consequently result in different signals in long baseline neutrino oscillation experiments.     

2002年诺贝尔物理奖的启示

本文论述2002年诺贝尔物理奖获得者,R.Davis在探测太阳中微子丢失的成就;M.Koshiba在证实存在太阳中微子丢失,探测超新星中微子和大气μ中微子丢失以及证明μ中微子振荡的成就。此外,本文还叙述2002年诺贝尔物理奖给我们的启示。     

Experimental and phenomenological status of neutrino anomalies

The current status of neutrino anomalies is summarized; the KamLAND experiment is described and the recent results of KamLAND presented.     

India-based Neutrino Observatory (INO)

We present some physics possibilities with an iron calorimeter detector (ICAL) and a status report on the feasibility study to construct such a detector at a future possible India-based Neutrino Observatory (INO). This talk was given at the workshop on high energy physics phenomenology, WHEPP-8, in Jan. 2004, at IIT Bombay.     

2002年诺贝尔物理奖的启示

本文论述2002年诺贝尔物理奖获得者，R．Davis在探测太阳中微子丢失的成就；M．Koshiba在证实存在太阳中微子丢失，探测超新星中微子和大气μ中微子丢失以及证明μ中微子振荡的成就。此外，本文还叙述2002年诺贝尔物理奖给我们的启示。     

Neutrino anomaly and ν-nucleus interactions

A review of various calculations of the inclusive quasi-elastic reactions and pion production processes in neutrino reactions for various nuclei at intermediate energies relevant to solar, atmospheric and accelerator neutrinos is presented     

Distinguishable RGE Running Effects Between Dirac Neutrinos and Majorana Neutrinos with Vanishing Majorana CP-Violating Phases

In a novel parametrization of neutrino mixing and in the approximation of τ-lepton dominance, we show that the one-loop renormalization-group equations （RGEs） of Dirac neutrinos are different from those of Majorana neutrinos even if two Majorana CP-violating phases vanish. As the latter can keep vanishing from the electroweak scale to the typical seesaw scale, it makes sense to distinguish between the RGE running effects of neutrino mixing parameters in Dirac and Majorana cases. The differences are found to be quite large in the minimal supersymmetric standard model with sizable tan β, provided the masses of three neutrinos are nearly degenerate or have an inverted hierarchy.     

Neutrinoless Double-Beta Decay and Neutrino Mass Spectrum

Implications of the neutrinoless double-beta (₀) decay searches for the neutrino mass and mixing spectrum are discussed. We consider properties of the effective Majorana mass, m _ee, relevant for ₀ decay. We find predictions or limits for m _ee in the three neutrino schemes which explain the atmospheric and solar neutrino data. We show how combined analysis of results from ₀-decay searches, oscillation experiments as well as direct measurements of neutrino mass will allow to identify the spectrum. In this connection, several test equalities which relate m _ee and the oscillation parameters in the context of certain neutrino spectra are suggested. Two issues are important for realization of the identification program: (i) high enough accuracy of determination of m _ee which requires reliable knowledge of the nuclear matrix elements, and (ii) possibility to identify the mechanism of the ₀ decay, in particular, to disentangle the decay due to exchange of the light Majorana neutrino and mechanisms related to exchange of heavy particles with m1/r _nuclei.