The top quark mass and flavour mixing in a seesaw model of quark masses

The top quark mass and the flavour mixing are studied in the context of a seesaw model of quark masses based on the gauge group SU(2)_L × SU(2)_R × U(1). Six isosinglet quarks are introduced to give rise to the mass hierarchy of ordinary quarks. In this scheme, we reexamine a mechanism for the generation of the top quark mass. It is shown that, in order to prevent the seesaw mechanism to act for the top quark, the mass parameter of its isosinglet partner must be much smaller than the breaking scale of SU(2)_R. As a result the fourth lightest up quark must have a mass of the order of the breaking scale of SU(2)_R, and a large mixing between the right-handed top quark and its singlet partner occurs. We also show that this mechanism is compatible with the mass spectrum of light quarks and their flavour mixing.