Limits on charged-scalar Yukawa couplings from $\tau$ and $B$ decays are discussed. They (and other existing limits) are consistent with "strong" couplings (∼1 for the third generation) even if the lightest scalar mass is in the range $20 \mathrm{GeV}\lesssim M_{\phi }\lesssim 100 \mathrm{GeV}$ but saturated in this case. $B(B\to \tau \nu X)$ and (for $M_{\phi }>m_t$) $B(T\to \tau \nu X)$ may be then as large as 30% and 70%, respectively. Both for $M_{\phi }<m_t$ and $M_{\phi }>m_t$ the potentially possible top-quark signature in $p\overline{p}$ collisions is $\tau +2\mathrm{}$ jets final state. The upper limit for $\tau \to \nu \eta \pi \mathrm{is}\simeq 0.003\%$.

• Received 24 August 1987

DOI:https://doi.org/10.1103/PhysRevLett.60.182