Supernova constraints on neutrino mass and mixing

In this article I review the constraints on neutrino mass and mixing coming from type-II supernovae. The bounds obtained on these parameters from shock reheating, r-process nucleosynthesis and from SN1987A are discussed. Given the current constraints on neutrino mass and mixing the effect of oscillations of neutrinos from a nearby supernova explosion in future detectors will also be discussed.     

Measurement of day and night neutrino energy spectra at SNO and constraints on neutrino mixing parameters

The Sudbury Neutrino Observatory (SNO) has measured day and night solar neutrino energy spectra and rates. For charged current events, assuming an undistorted 8B spectrum, the night minus day rate is 14.0%+/-6.3%(+1.5%)(-1.4%) of the average rate. If the total flux of active neutrinos is additionally constrained to have no asymmetry, the nu(e) asymmetry is found to be 7.0%+/-4.9%(+1.3%)(-1.2%). A global solar neutrino analysis in terms of matter-enhanced oscillations of two active flavors strongly favors the large mixing angle solution.     

Constraints on neutrino mixing

We explore the implications of imposing the constraint that two neutrino flavors (which for definiteness we take to be ν_μ and ν_τ) are similarly coupled to the mass basis in addition to the unitarity constraints. We allow three active and an arbitrary number of sterile neutrinos. We show that in this scheme one of the mass eigenstates decouples from the problem, reducing the dimension of the flavor space by one. This result allows significant simplification in the treatment of matter-enhanced neutrino transformation where multiple flavors and level crossings are involved.     

Constraints on three flavor neutrino mixing

We summarize the constraints on three flavor neutrino mixing coming from data. We first map out the allowed region in the three neutrino parameter space using solar and atmospheric neutrino data. We then incorporate the results of reactor and long baseline experiments in our analysis and show that the parameter space is drastically reduced. We conclude by pointing out that the results of Borexino and SNO will further help in constraining the parameter space.     

BBN constraints on neutrino and CNB

We discuss the BBN constraints on neutrino characteristics and the cosmic neutrino background in the case of neutrino oscillations. The general cases of non-zero initial population of the sterile state and non-zero lepton asymmetry are discussed as well.     

Supersymmetry constraints on the neutrino mass

Within the minimal supersymmetric extension of the Standard Model, the one-photon decay of the neutrino is studied on the basis of astrophysical, cosmological, and experimental data. Limits on the neutrino masses are obtained.     

Lepton mixing and neutrino oscillations

The present article is a review of phenomena connected with neutrino oscillations. Mixing of two neutrinos (Majorana as well as Dirac) with masses m₁ and m₂ is considered in detail. It is shown that the hypothesis of lepton mixing is not in contradiction with the existing data if |m₁²?m₂²| ? 1 (eV)². Possible experiments designed to reveal neutrino oscillations at reactor, meson factory and high energy accelerator facilities are considered. In such experiments oscillation might be found if $\text{|m}{}_1{}^2\text{?m}{}_2{}^2\text{| ? 0.01}\text{(eV)}{}^2$. The possibilities of searching for oscillations by experiments on cosmic ray neutrinos and especially on solar neutrinos are discussed in detail. The last experiments have an incredible high sensitivity from the point of view of testing the lepton mixing hypothesis (oscillation effects might be observable if $\text{|m}{}_1{}^2\text{?m}{}_2{}^2\text{| ? 10}{}^{\mathrm{?12}}\text{(eV)}{}^2$). The “solar neutrino puzzle” is also discussed from the point of view of lepton mixing. Neutrino oscillations are considered then in the case where in nature there exist N ? 2 neutrino types.In conclusion the case of heavy lepton mixing is considered. It is shown that in a concrete scheme with right-handed currents, the probabilities of such processes as μ → eγ, μ → 3e etc. can be close to existing experimental upper limits, provided the heavy lepton masses are of an order of a few GeV, whereas the probabilities of the above processes are entirely negligible if only neutrinos are mixed.     

Parameter counting for neutrino mixing

The content of physical masses, mixing angles and CP violating phases in the lepton sector of the extended standard model, both renormalizable and non-renormalizable, with arbitrary numbers of singlet and left-handed doublet neutrinos is systematically analyzed in the weak basis. Received: 25 April 2000 / Revised version: 16 June 2000 / Published online: 8 September 2000     

Parametrizing and rephasing neutrino mixing

Neutrino mixing in Standard Model extensions, both renormalizable and effective, with arbitrary numbers of singlet and left-handed doublet neutrinos is investigated in a systematic fashion. The charged and neutral (Z-boson-and Higgs-boson-mediated) lepton currents are written under a general Majorana condition, and the independence of observables from the choice of condition, rephasing invariance, is studied. A parametrization of the neutrino mixing matrices in the doublet-singlet factorized form is developed. Its relationship with the see saw mechanism is shown in the limit of small doublet-singlet mixing. The structure of the mixing matrices relevant to neutrino-oscillation experiments is explicated.     

Further limits on heavy neutrino couplings

Limits on leptonic mixing matrix elements are inferred from the results of a dedicated neutrino-decay search; an improvement of more than two orders of magnitude is achieved over previous results for a wide range of the neutrino mass.     

11B and constraints on neutrino oscillations and spectra from neutrino nucleosynthesis

We study the sensitivity to variations in the triple-alpha and 12C(α,γ)16O reaction rates, of the yield of the neutrino-process isotopes 7Li, 11B, 19F, 138La, and 180Ta in core-collapse supernovae. Compared to solar abundances, less than 15% of 7Li, about 25%-80% of 19F, and about half of 138La is produced in these stars. Over a range of ±2σ for each helium-burning rate, 11B is overproduced and the yield varies by an amount larger than the variation caused by the effects of neutrino oscillations. The total 11B yield, however, may eventually provide constraints on supernova neutrino spectra.     

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).     

Non-abelian gauge structure in neutrino mixing

We discuss the existence of a non-abelian gauge structure associated with flavor mixing. In the specific case of two flavor mixing of Dirac neutrino fields, we show that this reformulation allows to define flavor neutrino states which preserve the Poincaré structure. Phenomenological consequences of our analysis are explored.