Tau Neutrino Mass Research Articles

Estimation of Neutrino Masses Without Using Seesaw Mechanism

We propose the Bethe-Salpeter-like amplitude of spin operator in spin space and consider that the vibration of this spin operator amplitude causes the vibration in azimuthal angle space, which causes the anomalous magnetic moment of leptons and generates masses of flavor state neutrino. Under this consideration, we can estimate neutrino masses using anomalous magnetic moment of leptons instead of using conventional seesaw mechanism. Electron anomalous magnetic moment and muon anomalous magnetic moment have been measured precisely so that we can estimate the masses of electron and muon neutrino systemically in our consideration. For tau neutrino mass case, we cannot estimate it in our consideration because tauon anomalous magnetic moment has not been measured. Instead, we use the squared mass splitting data to estimate tau neutrino mass in this paper. These are not mass eigenstates masses but flavor states masses, however, the sum of these masses, which should be equal to the sum of mass eigen states masses, is consistent to the current upper and lower bound of the sum of neutrino masses for both cases of normal hierarchy and inverted hierarchy.

VectorlikeW±-boson coupling at TeV and third family fermion masses

In the third fermion family and gauge symmetry of the Standard Model, we study the quark-quark, lepton-lepton and quark-lepton four-fermion operators in an effective theory at high energies. These operators have nontrivial contributions to the Schwinger-Dyson equations for fermion self-energy functions and the ${W}^{\ifmmode\pm\else\textpm\fi{}}$-boson coupling vertex. As a result, the top-quark mass is generated via the spontaneous symmetry breaking of $⟨\overline{t}t⟩$-condensate and the ${W}^{\ifmmode\pm\else\textpm\fi{}}$-boson coupling becomes approximately vectorlike at TeV scale. The bottom-quark, tau-lepton and tau-neutrino masses are generated via the explicit symmetry breaking of ${W}^{\ifmmode\pm\else\textpm\fi{}}$-contributions and quark-lepton interactions. Their masses and Yukawa couplings are functions of the top-quark mass and Yukawa coupling. We qualitatively show the hierarchy of fermion masses and Yukawa couplings of the third fermion family. We also discuss the possible collider signatures due to the vectorlike (parity-restoration) feature of ${W}^{\ifmmode\pm\else\textpm\fi{}}$-boson coupling at high energies.

Properties of the Tau-Neutrino

The ν τ was postulated to exist after the discovery of the tau-lepton in 1975. First ν τ CC interactions was observed in 2000 by the DONuT experiment at Fermilab, which also set a limit on the magnetic moment. Electron positron collider experiments have studied the tau-lepton decays and measured the Michel parameters, the tau lifetime, and the number of the light neutrino species. In addition a direct upper limit of the tau-neutrino mass was measured. This paper gives a short review of the known properties of the tau-neutrino, along with preliminary results from DONuT on the measurement of the ν τ CC DIS cross section.

Hadronic EDMs in SUSY SU(5) GUTs with right-handed neutrinos

We discuss hadronic EDM constraints on the neutrino sector in the SUSY SU(5) GUT with the right-handed neutrinos. The hadronic EDMs are sensitive to the right-handed down-type squark mixings, especially between the second and third generations and between the first and third ones, compared with the other low-energy hadronic observables, and the flavor mixings are induced by the neutrino Yukawa interaction. The current experimental bound of the neutron EDM may imply that the right-handed tau neutrino mass is smaller than about 10 14 GeV in the minimal supergravity scenario, and it may be improved furthermore in future experiments, such as the deuteron EDM measurement.

Neutrinos in 5D SO(10) unification

We study neutrino physics in a 5D supersymmetric SO(10) GUT. We analyze several different choices for realizing the See-Saw mechanism. We find that the "natural" scale for the Majorana mass of right-handed neutrinos depends critically on whether the right-handed neutrinos are located in the bulk or localized on a brane. In the former case, the effective Majorana mass is "naturally" of order the compactification scale, about 10^{14} GeV. Note, this is the value necessary for obtaining a light tau neutrino mass approximately 10^{-2} eV which, within the context of hierarchical neutrino masses, is the right order of magnitude to explain atmospheric neutrino oscillations. On the other-hand when the right-handed neutrino is localized on the brane, the effective Majorana mass is typically larger than the compactification scale. Nevertheless with small parameters of order 1/10 - 1/30, an effective Majorana mass of order 10^{14} GeV can be accommodated. We also discuss the constraints on model building resulting from the different scenarios for locating the right-handed neutrinos.

CLEO contributions to tau physics

We review many of the contributions of the CLEO experiment to tau physics. Topics discussed are: branching fractions for major decay modes and tests of lepton universality; rare decays; forbidden decays; Michel parameters and spin physics; hadronic sub-structure and resonance parameters; the tau mass, tau lifetime, and tau neutrino mass; searches for CP violation in tau decay; tau pair production, dipole moments, and CP violating EDM; and tau physics at CLEO-III and at OLEO-c.

Limits on ντ mass by DELPHI

A limit on the tau neutrino mass is obtained using all the Z 0 → τ + τ − data collected at LEP by the DELPHI detector between 1992 and 1995. In this analysis events in which one of the taus decays into one charged particle, while the second τ decays into five charged pions (1–5 topology) have been used. The neutrino mass is determined from a bidimensional fit on the invariant mass m 5π ∗ and on the energy E 5 π of the five π ± system. The result found is m ν τ < 48.0 MeV/c 2 at 95% confidence level.

A biased review of tau neutrino mass limits

After a quick review of astrophysically relevant limits, I present a summary of MeV scale tau neutrino mass limits derived from accelerator based experiments. I argue that the current published limits appear to be too consistent, and that we therefore cannot conclude that the tau neutrino mass limit is as low as usually claimed. I provide motivational arguments calling into question the assumed statistical properties of the usual maximum likelihood estimators, and provide a prescription for deriving a more robust and understandable mass limit.

Review of the tau neutrino mass

The general techniques used in direct measurements of the tau neutrino mass, m ν τ , are introduced. This is followed by a review of the most recent experimental limits from the γ (4s) and LEP with a focus on the most recent measurement, that from CLEO using a new four-pion decay mode. A new ‘world average’ limit obtained by combining the likelihood functions of the CLEO, ALEPH and OPAL results is presented. The paper concludes with projections for potential results on this topic from the recently commissioned B-factory experiments, BABAR and BELLE.

Unification of gauge couplings and the tau-neutrino mass in supergravity without R parity

Minimal R-parity violating supergravity predicts a value for $alpha_s(M_Z)$ smaller than in the case with conserved R-parity, and therefore closer to the experimental world average. We show that the R-parity violating effect on the $alpha_s$ prediction comes from the larger two-loop b-quark Yukawa contribution to the renormalization group evolution of the gauge couplings which characterizes R-parity violating supergravity. The effect is correlated to the tau neutrino mass and is sensitive to the initial conditions on the soft supersymmetry breaking parameters at the unification scale. We show how a few percent effect on $alpha_s(M_Z)$ may naturally occur even with tau neutrino masses as small as indicated by the simplest neutrino oscillation interpretation of the atmospheric neutrino data from Super-Kamiokande.

Technique for direct eV-scale measurements of the Mu and tau neutrino masses using supernova neutrinos

Early black hole formation in a core-collapse supernova will abruptly truncate the neutrino fluxes. The sharp cutoff can be used to make model-independent time-of-flight neutrino mass tests. Assuming a neutrino luminosity of 10(52) erg/s per flavor at cutoff and a distance of 10 kpc, Super-Kamiokande can detect an electron neutrino mass as small as 1.8 eV, and the proposed OMNIS detector can detect mu and tau neutrino masses as small as 6 eV. We present the first technique with direct sensitivity to eV-scale mu and tau neutrino masses.

Erratum:CPviolation and matter effect in long baseline neutrino oscillation experiments [Phys. Rev. D 56, 3093 (1997)

We show simple methods how to separate pure CP violating effect from matter effect in long baseline neutrino oscillation experiments with three generations of neutrinos. We give compact formulae for neutrino oscillation probabilities assuming one of the three neutrino masses (presumably tau-neutrino mass) to be much larger than the other masses and the effective mass due to matter effect. Two methods are shown: One is to observe envelopes of the curves of oscillation probabilities as functions of neutrino energy; a merit of this method is that only a single detector is enough to determine the presence of CP violation. The other is to compare experiments with at least two different baseline lengths; this has a merit that it needs only narrow energy range of oscillation data.

Basis independent study of supersymmetry withoutRparity and the tau neutrino mass

In the most general R-parity violating model, including both bilinear and trilinear terms, the sneutrino receives a vacuum expectation value. We investigate the constraints on this vev following a basis independent approach, highlighting the relations between the three most popular basis. We study the prediction for the tau neutrino mass which follows from the minimization of the scalar potential in a SUGRA model with universality of the soft parameters at the GUT scale. Finally we show that the tau neutrino mass controls the R-parity violating effects both in the fermionic and scalar sectors.

L/ E-flatness of the electron-like event ratio, in Super-Kamiokande and a degeneracy, in neutrino masses

We show that the L/ E-flatness of the electron-like event ratio in the Super-Kamiokande atmospheric neutrino data implies the equality of the expectation values for the muon and tau neutrino masses. We establish this result by obtaining a set of three constraints on the neutrino-oscillation mixing matrix as contained in the indicated flatness. The resulting 3×3 neutrino-oscillation matrix depends only on one angle. A remarkable result that follows directly from this matrix is the consistency between the mixing angles observed by LSND and Super-Kamiokande.

Top-quark phenomenology in models with bilinearly and spontaneously broken R-parity

We study unconventional decays of the top-quark in the framework of SUSY models with spontaneously broken R-parity. In particular we discuss an effective theory which consists of the MSSM plus bilinearly broken R-parity. We demonstrate that the decay modes t→ τ ̃ + 1 b and t→τ + b ̃ 1 can have large branching ratios even in scenarios where the tau-neutrino mass is very small. We show that existing Tevatron data already probe the theoretical parameters, with promising prospects for further improvement at the Run 2 of the Tevatron.

Constraints on anomalous charged current couplings, tau neutrino mass and fourth generation mixing from tau leptonic branching fractions

We use recent experimental measurements of tau branching fractions to determine the weak charged current magnetic and electric dipole moments of the tau and the Michel parameter η with unprecedented precision. These results are then used to constrain the tau compositeness scale and the allowed parameter space for Higgs doublet models. We also present new constraints on the mass of the tau neutrino and its mixing with a fourth generation neutrino.

Implications of the νμ → νs solution to the atmospheric neutrino anomaly for early Universe cosmology

By numerically solving the quantum kinetic equations we compute the range of parameters where the ν μ → ν s oscillation solution to the atmospheric neutrino anomaly is consistent with a stringent big bang nucleosynthesis (BBN) bound of N eff BBN ≲ 3.6. We show that this requires tau neutrino masses in the range m ν τ ≳ 4 eV (for | δm atm 2| = 10 −2.5 eV 2). We discuss the implications of this scenario for hot+cold dark matter, BBN, and the anisotropy of the cosmic microwave background.

Atmospheric and solar neutrinos with a heavy singlet

We follow a minimalistic approach to neutrino masses, by introducing a single heavy singlet N into the standard model (or supersymmetric standard model) with a heavy Majorana mass M, which couples as a single right-handed neutrino in a Dirac fashion to leptons, and induces a single light see-saw mass m ν ∼5×10 −2 eV, leaving two neutrinos massless. This trivial extension to the standard model may account for the atomospheric neutrino data via ν μ → ν τ oscillations with near maximal mixing angle θ 23∼ π/4 and Δ m μτ 2∼2.5×10 −3 eV 2. In order to account for the solar neutrino data the model is extended to SUSY GUT/ string-inspired type models which can naturally yield an additional light tau neutrino mass m ν τ ∼few×10 −3 eV leading to ν eL →(cos θ 23 ν μL −sin θ 23 ν τL ) oscillations with Δ m e1 2∼10 −5 eV 2 and a mixing angle sin 22 θ 1≈10 −2 in the correct range for the small angle MSW solution to the solar neutrino problem. The model predicts ν eL →(sin θ 23 ν μL +cos θ 23 ν τL ) oscillations with a similar angle but a larger splitting Δ m e2 2∼2.5×10 −3 eV 2.

Three neutrinoΔm2scales and the singular seesaw mechanism

It is shown that the singular seesaw mechanism can simultaneously explain all the existing data supporting nonzero neutrino masses and mixing. The three mass-squared differences that are needed to accommodate the atmospheric neutrino data (through $\nu_\mu - \nu_s$ oscillation), the solar neutrino data via MSW mechanism (through $\nu_e - \nu_\tau$ oscillation), and the positive result of $\nu_\mu - \nu_e$ oscillation from LSND can be generated by this mechanism, whereas the vacuum oscillation solution to the solar neutrino problem is disfavored. We find that the electron and tau neutrino masses are of order $10^{-3}$ eV, and the muon neutrino and a sterile neutrino are almost maximally mixed to give a mass of order 1 eV. Two heavy sterile neutrinos have a mass of order 1 keV which can be obtained by the double seesaw mechanism with an intermediate mass scale $\sim 10^5$ GeV. A possible origin of such a scale is discussed.

Minimal supergravity with R-parity breaking

We show that the minimal R-parity breaking model characterized by an effective bilinear violation of R-parity in the superpotential is consistent with minimal N = 1 supergravity unification with radiative breaking of the electroweak symmetry and universal scalar and gaugino masses. This one-parameter extension of the MSSM-SUGRA model provides therefore the simplest reference model for the breaking of R-parity and constitutes a consistent truncation of the complete dynamical models with spontaneous R-parity breaking proposed previously. We comment on the lowest-lying CP-even Higgs boson mass and discuss its minimal N = 1 supergravity limit, determine the ranges of tanβ and bottom quark Yukawa couplings allowed in the model, as well as the relation between the tau neutrino mass and the bilinear R-parity violating parameter.