0000000000297619
AUTHOR
Cecilia Jarlskog
Neutrinoless double electron capture as a tool to measure the electron neutrino mass
Abstract 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 112 Sn → 112 Cd 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 di…
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.
Phenomenology of supersymmetry with broken R-parity
Abstract In some phenomenological supersymmetric models R -parity (+1 for particles, −1 for sparticles) is spontaneously broken along with tau-lepton number L τ by a vacuum expectation value υ τ of the tau sneutrino ν τ . To avoid excess stellar energy loss through majorons, there should also be explicit L τ violation through right-handed neutrinos. To have a sufficiently light ν τ , either υ τ is very small which is unnatural and boring, and/or the Higgs mixing parameter ϵ is very small. We find that in the limit ϵ → 0: -both the forward-backward asymmetry in e + e − → τ + τ − and the τ lifetime are unchanged, -Z 0 → ggν⊥ decays are possible where ν τ is an extra neutrino, -squarks and glu…
Polarizability contribution to energy-levels of muonic helium (mu4he)
An experiment measuring the 2S-2P separation in the ion ( mu /sup 4 /He)/sup +/ is in progress at CERN. Comparison of the outcome of this experiment with the prediction of quantum electrodynamics requires the knowledge of the hadronic correction due to the two-photon exchange mechanism. Therefore, the authors have calculated the correction to the energy levels of the ion ( mu /sup 4/He)/sup +/ due to this mechanism. The hadronic contribution to the 2S-2P separation is found to be approximately 16 AA which is about three times larger than the expected experimental uncertainty.
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…
Origin of discrepancy in theoretical value of polarizability correction to (mu-he-4)+ energy-levels
Different approaches in calculating the polarizability correction to the energy levels of the muonic 4 He ion are compared. These calculations disagree with each other by giving results 3 to 10 times larger than the experimental uncertainty. The origin of the major discrepancy is traced to the treatment of the nuclear excitations. It is shown that the experimental value of the electric polarizability of 4 He provides a crucial restriction on model calculations.
Non-decoupling of Heavy Neutrinos and Lepton Flavour Violation
We consider a class of models predicting new heavy neutral fermionic states, whose mixing with the light neutrinos can be naturally significant and produce observable effects below the threshold for their production. We update the indirect limits on the flavour non-diagonal mixing parameters that can be derived from unitarity, and show that significant rates are in general expected for one-loop-induced rare processes due to the exchange of virtual heavy neutrinos, involving the violation of the muon and electron lepton numbers. In particular, the amplitudes for $\mu$--$e$ conversion in nuclei and for $\mu\to ee^+e^-$ show a non-decoupling quadratic dependence on the heavy neutrino mass $M$,…
CP violation in decay rates of charged bottom mesons
In the standard theory we discuss a mechanism of interference between two different tree-level charged current amplitudes to induce CP violation. The asymmetry between conjugate Cabibbo disfavoured modes of charged bottom meson decays is considered. Estimates for two-body decays ofB u andB c are presented. We find thatB u − →D −+D 0 * , for instance, can give a big CP asymmetry with values ≈1–50%, depending on the angle and phase parameters.