CP violation in the rare Higgs decays via exchange of on-shell almost degenerate Majorana neutrinos, $H \to \nu_k N_j \to \nu_k \ell^{-} U {\bar D}$ and $H \to \nu_k N_j \to \nu_k \ell^{+} {\bar U} D$

TL;DR

This paper explores CP violation in rare Higgs decays mediated by nearly degenerate Majorana neutrinos, analyzing potential observability at the ILC through decay asymmetries involving quark channels.

Contribution

It introduces a detailed analysis of CP violation in Higgs decays via on-shell Majorana neutrinos, including oscillation effects and potential detection prospects.

Findings

CP asymmetries can be significant in certain parameter ranges.

Decays with open quark channels could be detectable at the ILC.

Oscillation effects influence the CP violation signals.

Abstract

We investigate rare decays of Higgs via exchange of two almost degenerate heavy on-shell Majorana neutrinos $N_j$ ($j=1,2$): $\Gamma_{\pm} = \Gamma(h \to \nu_k N_j \to \nu_k \ell^{\pm} \pi^{\mp})$, and into the open quark channels $\Gamma_{\pm} = \Gamma(h \to \nu_k N_j \to \nu_k \ell^{\pm} U D)$, where $U D$ are two jets of open quarks (${\bar U} D$, or $U {\bar D}$, where $U=u, c$ and $D=d, s$). The related CP violation asymmetry $A_{\rm CP} = (\Gamma_{-} - \Gamma_{+})/(\Gamma_{-} + \Gamma_{+})$ is studied in detail. We take into account the $N_1$-$N_2$ overlap and oscillation effects. We can see that for certain, presently acceptable, range of input parameters, such decays with open quark channels, and their asymmetries, could be detected in the International Linear Collider (ILC).