58 of 58 people found the following review helpful:
4.0 out of 5 stars
A first step to QFT, April 21, 2008
This review is from: Quantum Field Theory Demystified (Paperback)
I find it humorous to read some of the criticisms made of this book. It's clear that the people that have criticised it harshly were expecting a completely different book, perhaps McMahon's recommended next-step book "QFT in a Nutshell" by A. Zee. David McMahon, in my view, didn't set out to rewrite Zee's classic, so it's ridiculous to criticise him for not doing so.
In my view, McMahon set out to write a book to bridge the wide gap between QM and QFT. Many undergraduates come out of a QM course eager to learn QFT, but fall flat on their faces when confronted with some of the more inpenetrable graduate-level texts. Zee has done a good job of bridging some of that gap, but even Zee is a formidable read for someone who has just come out of a QM course. This is where I think McMahon has done a terrific job.
QFT Demystified is wonderful for those people that know QM and have attempted to read Zee but were still having trouble. "Demystified" will not explain everything in detail, but will paint the landscape with a broad brush so that you don't get mired in the detail. It will not explain every step presented, but if you can persevere and simply assume some of the results to be true, you'll find that in your next text (probably Zee) it will get derived in detail.
My main problem with the book (indeed, with all the Demystified books) is the rushed feel they have to them - it doesn't appear that enough time has been spent editing them, and the book is filled with typos that can be confusing to the beginner. This is unfortunate, since it is this sort of beginner that the book is targeted at in the first place.
In short - if you're a novice keen to start with QFT, and find even the beginner's books heavy going, you can't go wrong with McMahon. If you can overlook the typos, this book fills a niche that desperately needed to be filled.
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34 of 34 people found the following review helpful:
4.0 out of 5 stars
at least it's a start, June 14, 2008
This review is from: Quantum Field Theory Demystified (Paperback)
I ordered this book after I went through the first seven chapters of David Griffiths' "Introduction to Elementary Particles" and decided I wanted something that concentrated a little more on the theoretical side. Of course I didn't expect this book to be more than a peek into the mysteries of QFT, and the author is careful in the Preface to outline its limitations ("By design, this book is not thorough or complete....after completing this book, you will find that studying other quantum field theory books will be easier.") I hope he's right! I'm going to try tackling Zee next.
Anyway, I think the book is OK given the obvious challenges of trying to present QFT in an understandable way to a novice. I certainly didn't get everything, but I did manage to understand most of the material and get most of the problems in the Quizzes. But I wonder if I would have found it intelligible if I had not already read Griffiths as well as Schutz's "A First Course in General Relativity", which gave me some familiarity with special relativity, the metric, the Einstein summation convention, the covariant derivative, etc. This would seem to be considerably more than than a background in "basic special relativity" which the author lists in the Preface as one of the prerequisites for understanding his book. In some sections it was only by cross-referencing Griffiths that I was able to be sure I understood the material, and to correct errors in the text.
There are unfortunately plenty of errors, not as many as in "Quantum Mechanics Demystified" but still enough to give the strong impression that the author is either not putting much effort into proofreading, or delegating the task to less-than-fully-qualified individuals. McGraw-Hill should really do its readers/customers a favor and set up an erratum website. The author refers to one in his own website but it is not set up. The majority of the errors are minor arithmetical ones, but even these can often cause considerable confusion while the reader struggles to be sure it's not himself who is in the wrong. (Or are they a deliberate, diabolical strategy to force the reader to actually go through all the calculations?) But some are substantive and seriously interfere with comprehension. There's also an annoying tendency to be sloppy with the notation (or is the author trying to get the reader used to "sloppy physicist's notation"?) and to misplace superscripts and subscripts.
For learning the Feynman rules, Griffiths Chapter 7 is much clearer. But after cracking my skull fruitlessly for hours on Griffiths problem 7.24, I was delighted to find it worked (albeit erroneously, see below) on pages 179-83, so I was able to find where I had gone wrong (just one wrong minus sign in the momenta, durn it!) The exposition of spontaneous symmetry breaking, the Higgs mechanism, and electroweak theory are nice for a beginner (now I'll do Griffiths Chapter 10 and 11).
The following are a list of the most significant errors I've found that I'm relatively certain of (whenever possible by cross-referencing with Griffiths).
pages 16-17: charges of strange and charmed quark switched
page 32-34: in example 2.3, what happened to finding the Hamiltonian?
page 37: the equation representing conservation of energy at the bottom of the page is wrong: it should read d(mu)T(superscript mu)(subscript 0) equals 0.
page 43: equation just before section on Gauge Transformations should have "J(superscript nu)", not "J(superscript mu)".
page 87: second equation is described as "using the notation of Chap. 1" when in fact the notation for unit vector "e carat" was not introduced in Chap. 1 and makes its first unexplained appearance here.
page 103: first equation (p-m)(p+m) should read (pslash-m)(pslash+m) and third equation (p-m)u(p)=(p-m)(p+m)u(0) p should also be pslash.
page 104 helicity operator is sigma vector dot p carat, not sigma vector dot p vector (I think).
page 118 statement the "we..demote position and momentum from their lofty status as operators" would appear to contradict statement on bottom of page 4 that "momentum continues to play a role as an operator".
page 150: Figure 7.7 has errors in labelling of incoming and outgoing particle lines.
page 157: first 4 equations should have delta(q-p3-p4), not delta(q-p3+p4).
page 159: last equation should omit (2pi)^4 delta(p1-p2-p3-p4) term.
page 161: Figure 7.17 is for Question 2, not Question 1.
page 169:last 3 equations denominator should be sqrt(2p0)(2pi)^3/2 (see page 135).
page 177: in third and following equations, the second gamma matrix should be gamma(superscript nu), not gamma(superscript mu). Also, there should be another delta function term for the other vertex: (2pi)^4 delta(q+p2-p4), and an integration factor d4q/(2pi)^4. In general, Chapter 8 would greatly benefit from a clear, simple listing of the Feynman rules as Griffiths does in Chapter 7 section 5 of his book.
page 179: according to Griffiths, sqrt(E+m) IS the normalization factor.
page 183: second set of equations is for the RIGHT term of Equation 8.19, and should end up equalling 2p(i-1), not 2p(1-i), because g11=g22=-1. This gives M=-2g(subscript e)^2 which is the correct answer according to Griffiths (page 253 problem 7.24). But regardless, this is not the correct approach to solving the equation. It does not use the Einstein summation convention for the gamma matrices. See next note.
page 185: this equation for absolute value of M squared is wrong and would have rendered the whole section incomprehensible if I didn't have Griffiths to refer to. The equation should read g(subscript e)^4/4q^4[Tr(pslash3+m)(gamma(superscript mu))(pslash1+m)(gamma(superscript nu))]x[Tr(pslash4+m)(gamma (subscript mu))(pslash2+m)(gamma(subscript nu))].
page 202: first equation leaves out term -1/4(phi1^4+phi2^4) on left side and -3/2m2chi2 on right side, which would make correct final form
-m^2chi^2. Then we get "a field chi with mass m and a field PSI (not chi) that is massless".
page 212: first equation: delete "1/2". Second equation is gamma (subscript 5)^2, not ^5.
page 216: first equation, unclear where last term (i Lbar gamma (superscript mu) d(subscript mu)L" comes from. Also first term should be preceded with i.
page 217: second sentence missing a word: "preserve _____ of the action..."
page 220: according to calculations on page 212, term 10.30 should equal zero!
page 226: first line: where does the term (Dsubscriptmu phi)dagger (Dsubscriptmu phi) come from? In any event this should be (Dsubscript mu phi)dagger (Dsuperscriptmu phi).
page 237: integrand in second equation should be exp[-ax^2/2+bx].
Other suggestions to improve comprehension:
page 78: a statement that A(superscript mu) is the wavefunction of the photon would be useful here rather than waiting until page 166.
page 86: statement made that "In Chap. 4 we saw that this was due to ... " Show me where this is discussed in Chap. 4!
page 141: discussion of the interaction picture is garbled. Which picture is in the middle? And why?
page 151: it should be made explicitly clear that signs of momentum are opposite signs of direction for external antiparticle lines.
page 154: some explication of equation 7.18 would be nice: I found it in Griffiths.
page 155: some note that k is equivalent to q would be demystifying.
page 174: are we supposed to just accept equations 2 and 3 as given, or be able to derive them ourselves?
page 202: would help to put the term "vector bosons" in the Index and/or reference definition on page 76.
Too bad the answers to the quiz and final exam questions aren't worked out for the reader's benefit.
All in all though, it's a nice start!
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75 of 87 people found the following review helpful:
2.0 out of 5 stars
a sloppy workbook in QFT and Elementary particles, March 24, 2008
This review is from: Quantum Field Theory Demystified (Paperback)
The biggest sin of this text, forgetting for a moment the numerous typos and some apparent gray spots in the author's understanding, is the fact it doesn't 'demystify' anything. Quite the opposite, it turns QFT and the Standard Model into some kind of underexplained set of rules that one has to memorize - good for organizing your memory, bad for understanding. Basically this is how one teaches a parrot how 'to talk'. The text is only valuable as a workbook during the first quarter of QFT and Elementary particle courses, provided one follows the algebra manipulations without reading too much in the author's explanations. Just relying on this book to 'grasp QFT' will simply turn you into a parrot that can repeat a phrase precisely but has no clue what it means.
Renormalization or Quantum Chromodynamics are not discussed - those are a logical mess by themselves, I can imagine how less sense they would make in the hands of this author. I was planning on getting his 'String theory demystified' but after seeing how well he 'demystified' the simpler QFT I will pass on that. I simply don't believe mindless manipulations lead to understanding.
The book is full of typos: wrong signs clashing with the text just before the formula, mixing up upper and lower indices. Some of the intermediate manipulations are wrong too, while the final answers are almost always 'mysteriously' right lol The duplicate figures everywhere make it apparent that neither the author nor the editor cared enough about the readers to proof-read the text even once.
Some of the sloppy 'derivations' are so wrong it's mind-boggling. On page 6, McMahon 'proves' ct^2 - x^2 - y^2 - z^2 = ct'^2 - x'^2 - y'^2 - z'^2 by considering the particular case of light signal emitted from the origin for which both sides are zero. You won't see such a 'derivation' anywhere else because a particular case cannot prove a general case lol The 'derivation' of Noether's theorem for coordinate transformations on page 36 doesn't make sense at all if you try to follow it carefully because the notation is so imprecise it manages to fog the logic.
Some statements are simply put wrong, or the language is so sloppy it makes them wrong. Examples:
- page 37, according to McMahon, the conservation of energy means that the energy density remains constant with time. Yeah right ...
- page 45, he claims that we consider local gauge transformations vs. global because the local ones "satisfy special relativity that no signal can travel faster than the speed of light". Gauge transformations, local or global, have nothing to do with propagation of signals though ...
- page 81, "If the laws of physics are unchanged under time reversal, they are a symmetry of the system". How exactly a law of physics is 'a symmetry of the system'?!?
- page 171, the necessity of local gauge invariance is explained by "Physically (and experimentally) we find invariance in nature and so we will insist our theory also has invariance". Thats is as 'deep' as claiming that just because some systems in nature are rotationally invariant then all systems we ever happen to study must be rotationally invariant. The gauge invariance of Standard model is a guess by analogy with electromagnetism consistent with the experimental data, it doesn't mean all new theories have to be gauge invariant.
- page 188, he claims that local gauge symmetries which 'preserve causality as required by special relativity' are necessary to ensure local conservation of charge. News flash: a global gauge symmetry leads to local conservation of charge.
- page 203, he says a gauge field is 'invariant'(not changing) under a gauge transformation when he meant 'covariant'(transforming in a certain way).
Such a sloppy usage of the words 'invariant' and 'symmetry' all over the place is not helping beginners understand their meaning. Publishing a text like that, with so many typos, logical omissions or misconceptions, at the same type promising to 'demystify' is simply put inconsiderate to the readers. And god knows there are enough bad textbooks in QFT to add one more.
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