ABSTRACT
Sources are introduced to give an idealized description of the creation and the detection of particles. But the purpose of this activity is to study the properties of the particles, and this takes place in some region intermediate between the locations of the terminal acts of creation and detection. Thus one needs a convenient measure of the strength of the excitation that is produced in a region that may be far from its sources. The natural way to obtain such a measure is by investigating the effect on a probe or test source that is introduced into the region of interest. Accordingly, considering spin 0 particles and their real scalar sources, as represented by () W ( K ) = 1 2 ∫ ( d x ) ( d x ′ ) K ( x ) Δ + ( x − x ′ ) K ( x ′ ) , https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780429498480/0309ba2e-b9c4-492d-845b-8317c86c1176/content/eq1226.tif"/>
