Michel parameters in the presence of massive Dirac and Majorana neutrinos

Abstract

We analyse the effects of Dirac and Majorana neutrinos on leptonic decays of muon and tau leptons using the most general four-lepton effective interaction Hamiltonian of dimension six. We calculate the specific energy and angular distribution of the final charged lepton, including the polarizations of the initial and final charged leptons. We discuss the new generalized Michel parameters and focus on the effects of the heavy neutrino masses that would lead to sizable contributions on scenarios where the new sterile neutrinos have non-negligible mixing. Specifically, the most promising scenario is found for the case of $\tau$ decay with one heavy final-state neutrino with a mass around $10^2-10^3$ MeV, where the linear term suppression could be of order $10^{-4}$, low enough to be measured in current and forthcoming experiments.

37 pages, 6 figures. Matches published version, wording corrections were made and a realistic example was added, (see new Fig. 5)

References in corpus (10)

• The anomalous magnetic moment of the muon in the Standard Model
• Third order corrections to the semi-leptonic \boldmath{$b\to c$} and the muon decays
• Heavy Neutrinos and the Kinematics of Tau Decays
• Effects of heavy Majorana neutrinos on lepton flavor violating processes
• Three-loop corrections to the muon and heavy quark decay rates
• Michel decay spectrum for a muon bound to a nucleus
• Inferring the nature of active neutrinos: Dirac or Majorana?
• Muon decay spin asymmetry
• Majorana neutrinos with effective interactions in B decays
• A new method for measurement of the Michel parameters that describe the daughter muon polarization in the ${\tau }^{-}\to {\mu }^{-}{\bar{\nu }}_{\mu }{\nu }_{\tau }$ decay

Cited by in corpus (4)

• Study of the muon decay-in-flight in the ${\tau }^{-}\to {\mu }^{-}{\bar{\nu }}_{\mu }{\nu }_{\tau }$ decay to measure the Michel parameter ${\xi }^{\prime }$
• Dirac-Majorana neutrinos distinction in four-body decays
• General Signals for Charged Lepton Flavor Violating Decays
• Can a Nonstandard Invisible Pair Mimic the Michel Distribution?