Increasing R_b and Decreasing R_c with New Heavy Quarks

If the b and c quarks mix with new heavy quarks of weak isospin I_3 = -1 and 0 respectively, then the Z -> b b(bar) (c c(bar)) rate is necessarily greater (smaller) than that of the standard model. This may be the reason for the R_b excess and R_c deficit observed at LEP. A possible consequence of this scenario is the prospective discovery of a new quark x with the dominant decay x -> c h, then h -> b b(bar), where h is a neutral Higgs boson.