Light Charged Higgs and Lepton Universality in W boson Decays

We study the effect of a light charged Higgs appearing in supersymmetric models containing two Higgs doublets on the measurement of leptonic branching ratios of the W boson at LEP. We show that the $2.8 \sigma$ excess of the branching ratio $W \to \tau \nu$ with respect to the other leptons correlates well with the existence of charged Higgs with mass close to the mass of the W boson which dominantly decays into $W^\star$ and a light CP odd Higgs boson $A$ with mass below $2m_b$, so that it decays into $\tau^+ \tau^-$ and $c \bar c$. There are no searches for the charged Higgs in this channel and thus it could be discovered in LEP data or at the Tevatron where it would be frequently produced in top quark decays.