Precision measurements at the Z resonance agree well with the standard
model. However, there is still a hint of a discrepancy, not so much in Rbβ by
itself (which has received a great deal of attention in the past several years)
but in the forward-backward asymmetry AFBbβ together with Rbβ. The two
are of course correlated. We explore the possibilty that these and other
effects are due to the mixing of bLβ and bRβ with one or more heavy quarks.Comment: 11 pages, 1 Figure, LaTex fil