Solutions to the R_b, R_c and alpha_s puzzles by Vector Fermions

Abstract

We propose two minimal extensions of Standard Model, both of which can easily accommodate the recent puzzling observations about the excess in $R_b$, the deficit in $R_c$ and the discrepancy in the low energy and high energy determinations of ${\alpha }_s$. Each model requires three additional heavy vectorial fermions in order to resolve the puzzles. The current phenomenological constraints and the new potential phenomena are also discussed.

12 pages, in LaTeX, postscript file also appear http://www.uic.edu/~keung/pub/rbrc.ps