QED: Vertex renormalisation; Please have Peskin and Schroeder book handy!
I have a question regarding a point in the QFT book of peskin and schroeder. Iv been working through renormalisation in QED, The 2-point corrections are simple enough, however in this book the 3-point function is a little more involved and I have some issues. Essentially id to produce the result of page 334, equation 10.45. Im happily standing at page 192, equation 6.47. Now however; I dont want to regularize with Pauli-Villas, but use the dimensional regularization. The parts that i really dont get are buts of page 334 equation that have epsilonxy, for example, i dont reallly understand where this is coming from. I know that anything with an index can be altered to involve informatino about dimension, but i dont see this part... equivalently I dont see why we need the -epsilon(1-z)^2 part....same sort of issue crops in equation 10.41 page 333; where 4--> 4-epsilon, In desperation i reason this via 4 being a the original dimension; then making this expansion, but its unsettling and probably wrong reasoning, can any please eludicate what going on here?
p.s. real sorry for the lack of latex use, last time I used this program seriously was long ago, Iv forgotten how it works, and tried to use it to no avail...sorry:(