THE TOP-QUARK MASS AND FLAVOR MIXING IN A SEESAW MODEL OF QUARK MASSES

The top quark mass and the flavour mixing are studied in the context o f a seesaw model of quark masses based on the gauge group SU(2)(L) X S U(2)(R) X U(1). Six isosinglet quarks are introduced to give rise to t he mass hierarchy of ordinary quarks. In this scheme, we reexamine a m echanism for the generation of the top quark mass. It is shown that, i n 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 partn er occurs. We also show that this mechanism is compatible with the mas s spectrum of light quarks and their flavour mixing. (C) 1997 Elsevier Science B.V.