One-loop contributions to $WWZ$ from a seesaw variant with radiatively-induced light-neutrino masses

Abstract

The experimental confirmation of neutrino mass and mixing disagrees with the picture of the Standard Model, and thus provides a good motivation to look for unknown physics. A seesaw variant in which neutrino masses are radiatively generated, with neutrinos characterized by Majorana fields and where a set of three hypothetical neutral heavy leptons are present, has been considered in the present work. We have calculated, estimated, and analyzed the contributions from virtual light and heavy neutrinos to the gauge vertex $WWZ$, in the context of a future electron-positron collider. We have found that contributions to both $CP$-even and $CP$-odd anomalous couplings are generated. Our estimations indicate that contributions as large as $~10^{-3}$ can be achieved in both cases. This is particularly interesting for the $CP$-odd effects, which are expected to appear in the framework of the Standard Model since the three-loop order, thus being quite suppressed. By considering the expected sensitivity of the International Linear Collider to this gauge vertex, we conclude that these new-physics effects would be within its reach for $e^+e^-$ collisions taking place at a center-of-mass energy of $800\,{\rm GeV}$.