  We analyze CP asymmetries of B \to \phi K_S and B \to \eta' K_S in a
supersymmetric grand unified theory in which only the third generation
sfermions contained in 10(Q, U^c, E^c) of SU(5) can have a different mass from
the others. One of the advantages of this nonuniversal mass model is that the
first two generation sfermion masses can be large whereas both (left and right
handed) stops are light so as to stabilize the weak scale. Therefore, we
studied a minimal supersymmetric standard model parameter region in which a
fine tuning in Higgs sector is relaxed owing to light masses of stops, gluino
and higgsinos. In such a parameter region, the chargino contribution is as
important as the gluino one. We show that the CP asymmetries of B \to \phi K_S
and B \to \eta' K_S can deviate from their standard model predicted values by
O(0.1) because of constructive interference between gluino and chargino
contributions.

High Energy Physics - Phenomenology