Light pseudoscalar η and H → ηη decay in the simplest little Higgs mode

The SU(3) simplest little Higgs model in its original framework without the so-called μ term inevitably involves a massless pseudoscalar boson η, which is problematic for b -physics and cosmological axion limit. With the μ term introduced by hand, the η boson acquires mass mη ∼ μ, which can be lighter than half the Higgs boson mass in a large portion of the parameter space. In addition, the introduced μ term generates sizable coupling of H-η-η. The Higgs boson can dominantly decay into a pair of η’s especially when mH below the WW threshold. Another new decay channel of H → Zη can be dominant or compatible with H → W+W− for mH above the Zη threshold. We show that the LEP bound on the Higgs boson mass is loosened to some extent due to this new H → ηη decay channel as well as the reduced coupling of H-Z-Z. The Higgs boson mass bound falls to about 110 GeV for f = 3− 4 TeV. Since the η boson decays mainly into a bb̄ pair, H → ηη → 4b and H → Zη → Zbb̄ open up other interesting search channels in the pursuit of the Higgs boson in the future experiments. We discuss on these issues.