ABSTRACT
The definition of the decay rate (also called decay width) of an unstable particle is best defined by considering its self-energy, () https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780429073601/03ca065d-1bf0-4218-811d-2f95276252a3/content/math_111.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/>
