e**********n
发帖数: 359 | 1 I'll try to use as few words as possible.
The difficulty in QFT is untra-violet divergence, which is caused by the
point particle model that contains infinitely high momentum. Suppose we have
a QFT T(e), where e is a parameter(e.g. the fine structure constant or
electron mass). T(e) gives a perturbation expansion of some quantity S. Due
to the altra-violet divergence, high order terms of S diverge, T(e) is thus
useless.
Step 1: impose a momemtum cut-off L so that the QFT becomes T(e,L). Note
t |
|
