Non-exponential Decays in Quantum Field Theory

We discuss the decay law of an unstable particle in a quantum fieldtheoretical framework, concentrating our attention on the short-timeregion.The frequency cut-off plays a remarkable role, both in thesuperrenormalizable and renormalizable case.Deviations from the exponential law are found at very short times,but the temporal scales involved are so short that no experimentalrealization seems realistic.