Z -> b b-bar Excess from R-Parity Violation

Abstract

The $\text{Zbb}$ excess, $\text{Zcc}$ deficit, and low left-right asymmetry $A_b$ may be explained by a single term $\text{lam}{C}^c{B}^c{B}^{\prime c}$ in the superpotential. This operator violates R-parity and requires a sequential 4th generation. 1-loop diagrams involving squark exchange interfere with the tree-level processes to give an excess of right-handed $b$ quarks, and a deficit of right-handed $c$ quarks. Though the coupling must be large ($\text{lam}\approx 2$ or $3$), the model is phenomenologically and cosmologically acceptable.

Comments: 4 pages, LaTeX, 1 figure (using epsf). Running of lambda added, typos fixed