Radiative Corrections to $\text{zbb}$ from Colored Scalars in a Model with Dynamical Symmetry Breaking

Abstract

Isodoublet color-octet scalar bosons appear in the low-energy limit of a natural extension of the Standard Model in which the electroweak symmetry is broken by a $t\bar{t}$ condensate. We briefly discuss the model and show that radiative corrections (involving these scalars) to the branching ratio $R_b=\Gamma (Z\to b\bar{b})/\Gamma (Z\to \mathrm{hadrons})$ are negative and thus place a stringent lower bound on the masses of the colored scalars. This turns out to be $\sim 400$ GeV with $m_t=150$ GeV and increases quadratically with $m_t$. It is emphasized that $R_b$ is a parameter that is well-determined experimentally and that theoretical estimates are relatively free from uncertainties emanating from hadronic corrections and are comparatively insensitive to the value of the top mass.

Comments: 9 pages + 3 figures (available upon request), TeX file. Saha Institute Preprint no. SINP-TNP/93-22 (December 1993)