Light Higgs decay modes of Z-boson in the left–right twin Higgs model

The left–right twin Higgs model predicts a light pseudoscalar boson ϕ0ϕ0 and opens up some new decay modes for Z  -boson, such as Z→f¯fϕ0 and Z→ϕ0γZ→ϕ0γ. We examine these decay modes in the parameter space allowed by current experiments, and find that the branching ratios can reach 10−810−8 for Z→b¯bϕ0, which should be accessible at the GigaZ option of the ILC. However, the branching ratios can reach 10−910−9 for Z→τ¯τϕ0 and Z→ϕ0γZ→ϕ0γ, which are hardly accessible at the GigaZ option.