CP violation from new quarks in the chiral limit

We characterize CP violation in the $SU(2) \times U(1)$ model due to an extra vector-like quark or sequential family, giving special emphasis to the chiral limit $m_{u,d,s}=0$. In this limit, CP is conserved in the three generation Standard Model (SM), thus implying that all CP violation is due to the two new CP violating phases whose effects may manifest either at high energy in processes involving the new quark or as deviations from SM unitarity equalities among imaginary parts of invariant quartets (or, equivalently, areas of unitarity triangles). In our analysis we use an invariant formulation, independent of the choice of weak quark basis or the phase convention in the generalized Cabibbo-Kobayashi-Maskawa matrix. We identify the three weak-basis invariants, as well as the three imaginary parts of quartets $B_{1-3}$ which, in the chiral limit, give the strength of CP violation beyond the SM. We find that for an extra vector-like quark $|B_i| \leq 10^{-4}$, whereas for an extra sequential family $|B_i| \leq 10^{-2}$