Limits on the neutrino mass and mixing angle from pion and lepton decays

Abstract

Motivated by a recent rather surprising conclusion based on the 1992 PDG data on the pion, kaon and lepton decays that if three generations of neutrinos are assumed to be massive and mixed, the heaviest neutrino, ν 3 , could have a mass in the range, 155 MeV < ∼ m 3 < ∼ 225 MeV, we have analyzed the latest 1995 data on the leptonic decays of pion, µ and τ with the assumption that three generations of neutrinos are massive and mixed. It is shown that when the radiative corrections are included and the constraint from partial decay widths is imposed, the 1995 data are consistent with three massless neutrinos with no mixing. Various limits on the neutrino mass and mixing angle implied by the 1995 data are presented together with a critique of the previous analysis.14.60.Pq, 13.35.-r Typeset using REVT E X *

Supersymmetry withoutRparity: Constraints from leptonic phenomenology

“…However, these restrictions were always found to be weaker than the constraints from the ratios (in contrast to Ref. [31]).…”

“…These (together with radiative corrections) would re-introduce trilinear RPV terms; however, as already noted, since supersymmetric scalar particles must be considerably more massive than the gauge bosons, their contributions can be expected to be very small. Partial decay widths for these processes are then given by 4.4) and Standard parameters are the Fermi constant G (see [31] for minor subtleties), the pion decay constant f π , and V ud CKM = the ud-component of the CKM quark-sector mixing matrix. R πℓ and R ℓ ′ are leading radiative corrections to the processes.…”

“…Neutrino mass bounds in this more general case are more complicated, and better constraints are in fact obtainable from analysis of charged current processes (to be discussed in detail in the next section) than from direct mass bounds on ν τ (or ν µ ) [30]. Based on such an analysis, Bottini et al [31] gave a general neutrino mass bound of 149 MeV for a massive neutrino that was an admixture of ν e , ν µ and ν τ . The present case differs from theirs since in the RPV framework the massive neutrino can also have gaugino and higgsino contributions.…”

Could the τ be substantially different from e and μ in the supersymmetric standard model?

“…(11) is borne out by exact numerical results from diagonalizing the neutral fermion mass matrix, as illustrated in Fig. 2, where the machine ν τ bound of 18.2 MeV [5] and the generic neutrino mass bound of 149 MeV, from charged current data [6]. The dependence of There are potentially much stronger bounds on neutrino masses from cosmological considerations which however depend on the decay modes and other assumptions so that a neutrino mass above an MeV is not definitely ruled out.…”

An upper limit on the

“…Indirect bounds on the mass of can also be derived from the decay rates of the tau. The most stringent of these limits is m < 48 MeV=c 2 at 95% condence level (CL) [6]. Direct bounds have been derived from the reconstruction of multi-hadronic decays of the tau and several experiments [7,8,9] have obtained similar limits of about 30 MeV=c 2 .…”