Searching for heavy neutrinos in $e^+ e^- \to W^+ W^-$: it is all about unitarity

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.

Figures (11)

• Figure 1: Feinman diagrams of the process $e^+ e^- \to W^+ W^-$ in toy model.
• Figure 2: The dependence of differential cross section at $\cos\theta = 0$ on the value of $\sqrt{s}$ for different masses $M_N$. Here, solid lines correspond to exactly unitary mixing, while dashed lines correspond to linearized mixing.
• Figure 3: Feinman diagrams of the process $e^+ e^- \to W^+ W^-$.
• Figure 4: The dependence of differential cross section at $\cos\theta = 0$ on the value of $\sqrt{s}$ for different masses $M_N$. Here, solid lines correspond to SM extension, while dashed lines correspond to toy model.
• Figure 5: The dependence of differential cross section at $\cos\theta = 0$ on the value of $\sqrt{s}$ for different masses $M_2$. Here, solid lines correspond to SM extension with three heavy neutrinos, dashed lines correspond to toy model with one heavy neutrino, dotted lines correspond to HeavyN model with three heavy neutrinos.