  A non-standard light CP-odd Higgs boson could induce a slight (but
observable) lepton universality breakdown in Upsilon leptonic decays. Moreover,
the mixing between such a pseudoscalar Higgs and $\eta_b$ states might shift
the mass levels of the latter, thereby changing the values of the
$m_{\Upsilon(nS)}-m_{\eta_b(nS)}$ splittings predicted in the standard model.
Besides, also the $\eta_b$ width could be broader than expected, with
potentially negative consequences for its discovery in both $e^+e^-$ and hadron
colliders.
