Importance of unitarity in the search for heavy neutrinos in $e^{+}{e}^{-}\to W^{+}{W}^{-}$

Abstract

We study the process $e^{+}{e}^{-}\to W^{+}{W}^{-}$ with the aim of estimating the prospects for observing heavy neutrinos contributions at future $e^{+}{e}^{-}$-colliders. In this work, we consider two implementations of heavy-light neutrino mixing: a linearized mixing approximation applied in popular models and an exact unitary mixing scheme. We conclude that the approximate realization leads to physically incorrect results for this process, while exact unitary mixing provides some signatures that can be experimentally checked.

Comments: 27 pages, 20 figures; major update, new section added; published version