Fourth-generation quark masses and Fritzsch mass matrices from Abelian family symmetry

We examine possible mass relations resulting from Fritzsch-type mass matrices for quarks in left-right-symmetric models with an Abelian family symmetry. While the three-generation model predicts no realistic mass relation, six possible schemes exist in the presence of a fourth generation of quarks (t’,b’), with realistic constraints on the quark masses. The most attractive scheme predicts ($m_{b\mathcal{’}}$-$m_b$)($m_{t\mathcal{’}}$-$m_t$)≃($m_{\mathrm{sb}}$ $m_b$ ${\mathcal{’}}_{\mathrm{ct}\mathcal{’}}^{13}$@B. When combined with the experimental constraints on the ρ parameter, this leads to $m_t$≤68 GeV, $m_{b\mathcal{’}}$≤46 GeV, and 145 GeV≤$m_{t\mathcal{’}}$≤310 GeV.