No Arabic abstract
Absorption of high-energy $bar{ u}_e$ over electrons above the W boson production threshold is reexamined. It is pointed out that, in the case of photon emissions along the direction of incident high-energy $bar{ u}_e$, the kinematically allowed average energy carried by the final state hard photon can be $leq 1%$ of the incident $bar{ u}_e$ energy above the W boson production threshold. The differential energy spectrum for the final state hard photon is calculated. We also discuss implications of our results for the prospective search of high-energy $bar{ u}_e$ through this final state hard photon.
We discuss some motivations for detecting high-energy neutrinos through the pure electroweak processes such as $bar{ u}_e e^-to W^- $ and $bar{ u}_e e^-to W^-gamma$. We argue that the latter process can be viewed as an enhancement to the former one. The event-rate enhancement is estimated.
The processes of neutrino production of electron-positron pairs, $ u bar u to e^- e^+$ and $ u to u e^- e^+$, in a magnetic field of arbitrary strength, where electrons and positrons can be created in the states corresponding to excited Landau levels, are analysed. The results can be applied for calculating the efficiency of the electron-positron plasma production by neutrinos in the conditions of the Kerr black hole accretion disc considered by experts as the most possible source of a short cosmological gamma burst.
We calculate the Doppler broadening of the $W^-$ resonance produced in $bar{ u}_e e^-$ collisions of cosmic anti-neutrinos with $E_{ u}approx 6.3 PeV$ with electrons in atoms up to Iron. Revisiting this issue is prompted by recent observations of PeV neutrinos by Ice-Cube. Despite its poor energy resolution, the $20%$ Doppler broadening of the resonance due to electronic motions can produce observable effects via non-linear neutrino absorption near the resonance. The attendant suppression of the peak cross section allows $bar{ u}_e$ to travel correspondingly longer distances. While this effect is unlikely to be directly detected in the near future, it may facilitate terrestrial tomography at depths of $sim 10 km$, complementing deeper explorations using the more frequent nuclear interactions at lower energies.
Distinguishing the Dirac and Majorana nature of neutrinos remains one of the most important tasks in neutrino physics. By assuming that the $tau^- to pi^- mu^- e^+ u$ (or $bar{ u}$) decay is resonantly enhanced by the exchange of an intermediate mass sterile neutrino $N$, we show that the energy spectrum of emitted pions and muons can be used to easily distinguish between the Dirac and Majorana nature of $N$. This method takes advantage of the fact that the flavor of light neutrinos is not identified in the tau decay under consideration. We find that it is particularly advantageous, because of no competing background events, to search for $N$ in the mass range $m_e + m_{mu} leqslant m_N leqslant m_{mu} + m_{pi}$, where $m_X$ denotes the mass of particle $X in { e, mu, pi, N }$.
QCD one-loop corrections to the semileptonic process $e^+ e^- to mu^- bar u_mu u bar d$ are computed. We compare the exact calculation with a ``naive approach to strong radiative corrections which has been widely used in the literature and discuss the phenomenological relevance of QCD contributions for LEP2 and NLC physics.