C. Jarlskog

A New Lepton - Quark Mass Relation in a Unified Theory

Abstract We argue that the observed quark and lepton masses are related at momenta larger than 1015 GeV as follows: mb = mτ, mμ = 3ms and me = md/3. We construct a model in which these factors of three arise naturally — because quarks come in three colors.

Neutrinoless double electron capture as a tool to measure the electron neutrino mass

A nucleus (Z, A) may capture two atomic electrons to become (Z − 2, A). For Majorana neutrinos this may occur with no neutrino emission, the process is a virtual mixing of the parent atom and the daughter atom with two electron holes. The process becomes real as the daughter atom de-excites. In some cases where the daughter nucleus is excited, the neutrinoless decay may be enhanced by its proximity to a virtual resonance. We identify the 112Sn → 112Cd transition as a good case. The no-neutrino lifetime for mν = 30 eV ranges from 1022 to 1027 years as a function of the insufficiently well determined distance to resonance. The signatures of the two- or no-neutrino modes are very different.

Matter instability in the SU(5) unified model of strong, weak and electromagnetic interactions

Abstract Previous estimates for the stability of matter through baryon-number violating nucleon decays are refined by taking into account all possible diagrams that contribute to the process. As a result, we obtain τ (p) ∼ τ (n) ∼ 10 33 y, not quite one order of magnitude smaller than previous estimates. Most of the decays will produce mesons, but no direct muon. Muon-producing decays are only ∼ 10% of all decays. Although the theoretical errors are large (about one order of magnitude) we conclude that, if the effect is there, and experiments sensitive to detection of mesons (and not only muons) are devised, an increase of two to three orders of magnitude in the present experimental accuracy may reveal it.

Parity violations by neutral currents in muonic atoms

Abstract The 2S-1S transition in low Z muonic atoms is shown to be extremely sensitive to possible parity violation, such as may introduced by neutral currents. The most striking effects of parity violation are found in the case of muonic Li and Be where they are estimated to be of the order of 10% on the basis of current models.

Neutrino counting at the Z-peak and right-handed neutrinos

Abstract We consider the implications of extending the minimal standard model, with n families of quarks and leptons, by introducing an arbitrary number of right-handed neutrinos, for neutrino-counting via the “invisible width” of the Z. It is shown that the effective number of neutrinos, 〈 n 〉, satisfies, the inequality 〈 n 〉 ⩽ n , where 〈 n 〉 is defined by Γ ( Z →neutrinos) ≡ 〈 n 〉 Γ 0 and Γ 0 is the standard width for one massless neutrino. Thus, in the case of three families, the neutrino-counting can give a result which is less than three, if there are right-handed neutrinos.

Muon capture at large energy transfer

Abstract A novel and parameter free approach to μ capture is introduced. The inclusive capture rate at maximal energy transfer is connected with the off-mass shell s and p wave scattering lengths for pions. Inside PCAC a rigorous lower bound for the rate results. The vector current contributions are shown to be insignificant. In a numerical illustration it is shown that this picture qualitatively explains the high energy nucleons emitted in μ capture.

Implications of gauge theories for heavy leptons

Abstract General features of heavy lepton production and decay are studied in the framework of a large number of gauge models. A convenient classification into SU(2) type and SU(3) type models is made according to the leptonic multiplets and allowed transitions. Striking differences are expected for the production and decay mechanisms of the two types of models. Associated strange particle production and the decay branching ratios should serve as helpful guidelines in searching for the correct gauge model.

Polarizability contributions to the neutron-lepton amplitude at threshold

Abstract Motivated by recent interest in the neutron-electron scattering amplitude at threshold, a detailed investigation of the two-photon exchange contribution, commonly known as the polarizability correction, to this amplitude is made, for general lepton mass. The contributions is related to the amplitude describing forward virtual Compton scattering on neutrons. To calculate it, we write dispersion relations for the Compton amplitudes and make use of the present knowledge of the neutron structure functions as well as the scaling hypothesis. The correction is much larger for muons than for electrons. Further, we discuss the region of validity of the extreme relativistic and the classical approximations treated in the literature by giving the relevant parameter which leads naturally from one case to the other.

Weak interaction corrections to e+e− annihilation processes and tests of unified theories of weak, electromagnetic and strong interactions

Abstract We calculate weak interaction corrections to R = σ( e + e − → all ) σ( e + e − → μ + sm − ) at high energies, using a quark parton model. We show that the correction due to interference between γ and Z mediated annihilations (which would make itself manifest by a variation linear in the square of the centre-of-mass energy) is strongly model dependent. In particular the γ-Z interference contribution to R vanishes identically (to the order g s 4 in the gluon coupling constant) in unified theories of weak, electromagnetic and strong interactions provided the lepton and quark masses are neglected as compared with the energy, and if perturbation theory is valid.

Neutral currents and the circular polarization of bremsstrahlung

Abstract Bremsstrahlung from lepton-nucleus scattering has a small circular polarization if the weak neutral currents are vector and axial vector. The magnitude of the effect is calculated for low incident lepton energies where the nuclear excitation may be neglected.