We study the time evolution of decaying particles in renormalizable models of
Relativistic Quantum Field Theory. Significant differences between the latter
and Non Relativistic Quantum Mechanics are found -in particular, the Zeno
effect seems to be absent in such RQFT models. Conventional renormalization
yields finite time behavior in some cases but fails to produce finite survival
probabilities in others.Comment: Revised version of the paper Time evolution and Zeno effect in
relativistic quantum field theory. To appear in Phys. Lett.