Hi
I am struggling to justify
D(x-y) \approx e^{-i m t} as t \rightarrow \infty
from
\int dE \sqrt{E^2-m^2} e^{-i E t} .
I thought I might get some insight from discretizing, as
e^{-i m t} \sum_{n=0}^{\infty} \epsilon \sqrt{ n \epsilon ( 2 m + n \epsilon ) } e^{-i...