Sorry for my questions, (it does seem like QFT triggers quite a lot of questions :-D). Anyway, on page 103 (it has a preview in google books), I am not sure how did he get equation (14.40), obviously it should follow from (14.39), but I don't understand where did -ln(m^2) disappear ? Shouldn't we have an expression like (14.40) but the term (linear in k^2 and m^2) be instead: (linear in k^2,m^2 and ln(m^2)). Cause as far as I can tell from (14.39) [tex]\Pi(k^2)[/tex] depends also on ln(m^2), and thus the term "linear in..." should be replaced with "linear also in ln(m^2)", cause as far as I can tell ln(m^2) isn't linear function of m^2, right? Hope someone can enlighten me.