From Fermion Mass Matrices to Neutrino Oscillations

We present an ansatz for the quark and lepton mass matrices, derivable from SO(10) type GUTs, which accommodates a heavy $(> 92 GeV)$ top quark and permits large mixings in the $\nu_\mu \leftrightarrow \nu_\tau$ sector (as suggested by the recent Kamiokande and IMB data on the atmospheric neutrinos). The well known asymptotic relations $m_b = m_\tau$, $m_s = \frac{1}{3} m_\mu$ and $m_dm_s = m_e m_\mu$ all hold to a good approximation. Depending on $\nu_\mu \leftrightarrow \nu_\tau$ mixing which can even be maximal, the mixing angle relevant for solar neutrino oscillation lies in the range $7.8 \times 10^{-3} \stackrel{_<}{_\sim} \sin^2 2\theta_{e\mu} \stackrel{_<}{_\sim} 2.1 \times 10^{-2}$. For the $^{71}$Ga experiment the event rate, normalized against the standard solar model prediction of 132 SNU, is estimated to be between 80 and 20 SNU.