Why they often consider zero mass limit when considering mass evolution(renormaliztn)

ndung200790

Please teach me this:
Why some books only consider zero mass limit when they consider the renormalization group.I have been wondered this because the mass parameter multiplying with relevent operator,it become growth when momentum grows.
Thank you very much in advance.

ndung200790

It seem that in high energy physics,we can consider the mass of particle is small.But how about the other physics?

ndung200790

''Zero mass limit'' I mean that we could use perturbative theory with mass parameter.