Realistic quark and lepton masses through SO(10) symmetry

In a recent paper a model of quark and lepton masses was proposed. Without any family symmetries almost all the qualitative and quantitative features of the quark and lepton masses and Kobayashi-Maskawa mixing angles are explained, primarily as consequences of various aspects of SO(10) symmetry. Here the model is discussed in much greater detail. The threefold mass hierarchy as well as the relations $m_{\tau }^0\simeq m_b^0,$ $m_{\mu }^0\simeq {3m}_s^0,$ $m_e^0\simeq \frac{1}{3}{m}_d^0,$ $m_u^0{/m}_t^0\ll m_d^0{/m}_b^0,$ $\tan {\theta }_C\simeq \sqrt{m_d^0{/m}_s^0},$ $V_{\mathrm{cb}}\ll \sqrt{m_s^0{/m}_b^0},$ and $V_{\mathrm{ub}}\sim V_{\mathrm{us}}{V}_{\mathrm{cb}}$ follow from a simple Yukawa structure at the unification scale. The model also gives definite predictions for $\tan \beta ,$ the neutrino mixing angles, and proton decay branching ratios. The $\left({\nu }_{\mu }-{\nu }_{\tau }\right)$ mixing angle is typically large, $\tan \beta$ is close to either $m_t^0{/m}_b^0$ or $m_c^0{/m}_s^0,$ and proton decay is in the observable range, but there is a group-theoretical suppression factor in the rate.