Rare Z-decay into light CP-odd Higgs bosons: a comparative study in different new physics models

TL;DR

This study compares predictions of rare Z-boson decays into light CP-odd Higgs bosons across various new physics models, highlighting potential observability at the GigaZ collider and their use in model discrimination.

Contribution

It provides a comparative analysis of rare Z decay modes into light CP-odd Higgs bosons in multiple new physics models, with predictions on branching ratios and experimental prospects.

Findings

Branching ratios can reach 10^{-4} for Z→f̄fa in some models

Decays Z→aγ have branching ratios around 10^{-9}

Decays Z→aaa can have branching ratios up to 10^{-3}

Abstract

Various new physics models predict a light CP-odd Higgs boson (labeled as $a$) and open up new decay modes for Z-boson, such as $Z \to \bar{f} f a$, $Z\to a\gamma$ and $Z\to aaa$, which could be explored at the GigaZ option of the ILC. In this work we investigate these rare decays in several new physics models, namely the type-II two Higgs doublet model (type-II 2HDM), the lepton-specific two Higgs doublet model (L2HDM), the nearly minimal supersymetric standard model (nMSSM) and the next-to-minimal supersymmetric standard model (NMSSM). We find that in the parameter space allowed by current experiments, the branching ratios can reach $10^{-4}$ for $Z \to \bar{f} f a $ ($f=b,\tau$), $10^{-9}$ for $Z\to a\gamma$ and $10^{-3}$ for $Z\to aaa$, which implies that the decays $Z \to \bar{f} f a$ and $Z \to a a a$ may be accessible at the GigaZ option. Moreover, since different models predict different patterns of the branching ratios, the measurement of these rare decays at the GigaZ may be utilized to distinguish the models.