convenient
131Feynman diagram — The Wick s expansion of the integrand gives (among others) the following termNarpsi(x)gamma^mupsi(x)arpsi(x )gamma^ upsi(x )underline{A mu(x)A u(x )};,whereunderline{A mu(x)A u(x )}=int{d^4pover(2pi)^4}{ig {mu u}over k^2+i0}e^{ k(x x )}is the… …
132Power law — A power law is any polynomial relationship that exhibits the property of scale invariance. The most common power laws relate two variables and have the form:f(x) = ax^k! +o(x^k),where a and k are constants, and o(x^k) is of x. Here, k is… …
