What are your opinions on Zeidler's QFT books? I am interested in mathematically rigorous treatment of quantum field theory, constructive QFT in particular.
I have read 'QFT, A Tourist Guide for Mathematicians' and am going to read "Quantum Physics, A functional integral point of view'. But I want something encyclopedic to refer to.
And I have come across the series of books by Zeidler. They are expensive to purchase.. so I ask opinions on the books in terms of the rigor achieved.
Are the books as rigorous as math books and papers? And would they be good reference for reading the book "Quantum Physics, A functional integral point of view'?
I welcome any feedback!!
 A: In general reading entire textbooks in QFT is not the best way to learn QFT (or any subject in science and mathematics).  I have not heard of the books, but my guess is that they are not going to be as rigorous as math books and papers as there is not a mathematically rigorous formulation of QFT (I'm sure you are aware that the basic problem of Yang-Mills existence and the mass gap is a Clay Institute Millennium Problem).
Also to be honest it has been a while since anyone has done anything in algebraic or axiomatic QFT which the wider community of field theorists really cares about.  This is my personal opinion on the matter, but one which is also expressed by some other theoretical physicists (see for example Modern Quantum Field Theory by Tom Banks).
Edit: If I remember rightly, you can find Steven Weinberg's lecture where he reflects on the fiftieth anniversary of his classic paper 'A Model of Leptons' and at the end he expresses similar sentiments about a mathematically rigorous formulation of QFT (ie. that it is important and desirable, but that he does not particularly care as such a formulation is unlikely to inspire any actual new physics).
A: In my opinion, Zeidler's books are good for getting a detailed overview of a lot of the different mathematical ideas and concepts undergirding modern efforts in QFT, if one already knows a fair bit of QFT. They are (again in my opinion) no good at all for learning QFT.
One major problem with the books is that they are often rather disorganized (the same concept is discussed twice in different chapters, different notation for the same thing is introduced in different places, etc.). The other major problem is that there are a lot of errors that indicate that proofreading and copyediting did not take place at all (e.g. some of the Feynman diagrams for QED are hilariously wrong). There are also lots of more minor problems. So unless you have a good idea of what precisely you want to learn, I'd advise you to stay away from these books.
