A method to limit the muon neutrino mass

Existence of a purely leptonic neutral current weak interaction may permit the use of ν_ω, e^? elastic scattering to limit the muon neutrino mass.     

New determination of the upper limit for the muon neutrino mass

We have measured the muon momentum in pion decay at rest using a magnetic spectrometer. From the result, p_μ⁺ = (29.787±0.005) MeV/c, we deduce a squared muon neutrino mass of (0.23±0.54) MeV²/c⁴.     

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.     

Implications of a 17 keV neutrino for baryogenesis

There is some experimental evidence for a 17 keV component of the electron neutrino, in the form of the recent observations of kinks in the beta-decay spectra of tritium, ¹⁴C, ³⁵S and ⁶³Ni. In this paper I show that most particle-physics models consistent with the 17 keV neutrino require a baryogenesis scale below 10⁶ GeV. Furthermore, models with a 17 keV neutrino typically contain new sources of CP violation, and the cosmological baryon asymmetry could be generated by anomalous electroweak interactions during a first-order weak phase transition.     

On the implications of a 17 keV neutrino

We discuss the implications of the recent measurement of a 17 keV mass component in the electron neutrino sector. Such a heavy state must decay in order to be compatible with cosmology; this requires states additional to those of the standard model. The most likely candidates are either majorons, allowing the decay into massless weakly interacting scalars, or single neutrinos, allowing the decay via the Z into light neutrinos. We show that in the latter case there is a lower bound on the lifetime in conflict with the cosmological constraints on this decay channel and on the photon plus neutrino decay channel which is also present. The extensions of the standard model needed to reduce the lifetime are considered. We analyze the mass matrix, playing particular regard to the singlet neutrino case, and discuss how it might be extended to explain the solar neutrino deficit.     

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.     

Lower limit for heavy muon mass obtained from the data of the CERN neutrino experiment

A lower limit for the heavy muon (heavy lepton omega′^? which can have the same lepton number as omega^? and ν_omega) mass M_μ′ > 1.8 GeV at 90% confidence level is obtained with the help of the bubble chamber “Gargamelle” data in the CERN neutrino experiment. This limit should not be confused with the known limit for an M⁺ (heavy lepton M⁺ which can have the same lepton number as μ^? and ν_μ).     

Search for T-violation in neutrino oscillation with the use of muon polarization at a neutrino factory

A possibility to search for T violation in neutrino oscillation with the use of muon polarization is studied. The sensitivity to T violation is examined with various magnitudes of muon polarization as a function of muon energy and long-baseline distances.     

Constraints on long-baseline neutrino oscillations from the results of neutrino oscillation experiments

It is shown that in the two schemes with four massive neutrinos which are compatible with the results of all neutrino oscillation experiments, the probabilities of disappearance and appearance in long-baseline experiments are severely constrained.     

T-odd correlation in muon neutrino elastic scattering on polarized proton target

In this paper, we analyze the elastic scattering of the muon neutrino (_νμ${\nu }_{\mu }$) beam on the polarized proton target (PPT) in a presence of induced couplings, and predict how the existence of relative phases between the complex vector (weak magnetism) and axial (induced pseudoscalar) form factors of the proton with left-chirality _νμ${\nu }_{\mu }$ affects the azimuthal dependence of the differential cross section. The neutrinos are assumed to be Dirac fermions with non-zero mass and CPT symmetry is conserved. We show that the azimuthal asymmetry of recoil protons depends on the neutrino mass, but contributions are very tiny (∼10⁻⁵$\sim {10}^{-5}$). Analysis of the differential cross section in the case of pure vector and axial couplings at zero _νμ${\nu }_{\mu }$ mass limit and zero momentum transfer shows that the T-violating phase _βVA${\beta }_{\mathit{VA}}$ generates the T-odd, P-even triple correlation and it could be detected by measuring the asymmetry between the (0,π)$(0,\pi )$ and (π,2π)$(\pi ,2\pi )$ angles. It should be clearly stressed that the considered T-odd observable is not a genuine CP-violating quantity as it can also be produced by the T-invariant contributions due to the final state interactions (FSI). Their magnitude must be precisely estimated and subtracted from the measured observable to extract information on the possible time reversal violation (TRV). We also indicate the possibility of using the PPT in the neutrino telescope.