Influence of Additional Fermions and Gauge Bosons on $Re(\epsilon'/epsilon)$

Abstract

The CP violation parameter $Re(\epsilon'/\epsilon)$ has previously been calculated in the standard model and the result depends on the top quark mass in an exciting way. We consider how the result is modified in two specific extensions of the standard model. The first adds only fermions, an extra vector-like quark doublet, and tends to reduce $Re(\epsilon'/\epsilon)$. The second contains three extended families with the third family treated differently and additional gauge bosons - the 331 model - and can accommodate larger values of $Re(\epsilon'/\epsilon)$ for a given $m_t$. When the experimental values of $m_t$ and $Re(\epsilon'/ \epsilon)$ are known more accurately, it will allow discrimination between theories. If the lower experimental number $Re(\epsilon'/\epsilon) = (0.74 \pm 0.60) \times 10^{-3}$ (Fermilab, E731) is confirmed and $m_t$ is near the value 175GeV the standard model is acceptable. But, if the higher value $Re(\epsilon'/\epsilon) = (2.3 \pm 0.65) \times 10^{-3}$ (CERN, NA31) persists, a dynamics like the 331 model where the third family is treated differently from the first two and there exist additional gauge bosons seems to be favored.