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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?

Cheers!

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:(