Finite-size corrections to Fermi's golden rule: I. Decay rates

TL;DR

This paper investigates finite-size effects on decay rates in quantum systems, revealing universal corrections to Fermi's golden rule that impact precision measurements in particle decay experiments.

Contribution

It introduces finite-size corrections to Fermi's golden rule, accounting for wave packet effects and their universal properties in relativistic quantum systems.

Findings

Decay probability depends on wave packet size and overlap.

Corrections distort energy distribution of decay products.

Universal properties applicable to relativistic systems.

Abstract

A quantum mechanical wave of a finite size moves like a classical particle and shows a unique decay probability. Because the wave function evolves according to the Schr\"{o}dinger equation, it preserves the total energy but not the kinetic energy in the intermediate-time region of a decay process where those of the parent and daughters overlap. The decay rate computed with Fermi's golden rule requires corrections that vary with the distance between the initial and final states, and the energy distribution of the daughter is distorted from that of plane waves. The corrections have universal properties in relativistically invariant systems and reveal macroscopic quantum phenomena for light particles. The implications for precision experiments in beta decays and various radiative transitions are presented.