Probing light pseudoscalar, axial vector states through η_(b) toτ⁺τ⁻

In this paper we explore the decay $\eta_b --> \tau^+ \tau^-$ as a probe for a light pseudoscalar or a light axial vector state. We estimate the standard model branching ratio for this decay to be $~4\times 10^{-9}$. We show that considerably larger branching ratios, up to the present experimental limit of ~8%, is possible in models with a light pseudoscalar or a light axial vector state. As we do not include possible mixing effects between the light pseudoscalar and the $\eta_b$, our results should be reliable when the pseudoscalar mass is away from the $\eta_b$ mass.