Customer Reviews

Quantum Field Theory Demystified

5 star:		(3)
4 star:		(5)
3 star:		(7)
2 star:		(1)
1 star:		(2)

 

 

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.

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!

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.

By reading this book alone, you will not master quantum field theory. You probably won't learn much except for some lingo and a few equations. However, if you pair this book with Griffiths Intro to Elementary Particles, or Zee's Quantum Field Theory in a Nutshell, then you will get great results! This helpful little book cuts straight to the important material. It is very much like an outline of basic quantum field theory, so the more you know all around (i.e. from lectures, other books, etc) the more use you will get from this book. I would especially recommend this book to anyone trying to self-study quantum field theory.

This is not the first book from which I try to completely understand QFT. A awaited the coming out of this book with a huge anticipation, because I already owned two other books written by the same author - about the non-relativistic quantum mechanics and about the general relativity, and I consider them great. Unfortunately, this book doesn't quite fit the bill. The reasons:

1. The connection between the Lagrangians and the Feynman rules is unclear (for instance, there is nothing mentioned about the Wick's theorem).

2. There is essentially nothing about the divergences and renormalization.

The reasons, why I don't criticize this book more harshly, are:

1. There seems to be no really good "introduction" level book about QFT

(the closest ones are Lahiri, "A First Book of QFT", Harris, "A Pedestrian Approach to QFT (out of print, used books expensive!), Greiner, "Field Quantization" and Hatfield, "QFT of Point Particles and Strings". But don't even approach any of these, if you hadn't mastered the Griffiths book about the elementary particles and the full-blown non-relativistic QM in Dirac's bra-ket notation !).

2. Lots of derivations present in this book are either completely omitted or "left for the reader" in other QFT books.

In other words, considering that QFT is the most difficult of the "ortodox", i.e. well established, physical theories, don't expect any "silver bullet" here. There is no such a bullet!

This book has been reviewed for content by several others. In that regard I agree with those who say that despite its warts (various typos and lapses in explanation) it is a good investment and valuable for those seeking to make sense of the usual scattered and disconnected treatments of QFT at the introductory level.

But I mean this review to be primarily about the Kindle version as the content has been reviewed by others. I strongly suggest you do not buy the Kindle version. The conversion from the book to the Kindle format was obviously made without ever looking at the result! It shows complete lack of editorial control (or self-respect) that this book would be offered for the Kindle.

As might be expected of a book on QFT, this book is filled with equations. Those equations that appeared "set off" from the text, that is between sections of text, were apparently converted to images and hence can be read, albeit in many cases the resulting symbols are incredibly small and cannot be enlarged by the Kindle. However, the approximately 25% of the equations that are "in-line" with the text cannot be read at all - any greek letters, mathematical symbols, etc. appear as boxed question marks. If you know your QM and QFT pretty well, you can read around and imagine what should be there, but its not pleasant and woe to the beginner.

Unfortunately this experience will make me leery of purchasing any Kindle book on a mathematical topic.

Sadly, this book is almost completely useless to learn quantum field theory.

There is actually very little quantum field theory discussed at all!

For example,

- Wick's theorem is not even mentioned!

- There is no mention of the LSZ reduction formula!

At this point, you might wonder how can the author derive the Feynman rules at all.

Good question. After writing the time evolution as a Dyson series, the author writes, I quote:

"Confused? Who wouldn't be. Luckily Feynman understood well enough this stuff to distill

it down to a simple recipe. We will forget everything we've done so far and use the Feynman rules

to calculate amplitudes"

He then just throws in the Feynman rules.

This is unacceptable given that the purpose of the book is supposedly to demystify

quantum field theory!

But it does not stop there. Feynman rules are only given for tree level processes.

There is no discussion of loop diagrams anywhere in the book! And therefore, no

discussion of regularization, renormalization, the renormalization group, Fadeev-Popov ghosts

and all the subtleties associated to loop dagrams.

Even worse, there are no explanations of how to calculate decay rates and cross sections!!

So there is not a single example of cross section or decay rate calculations in the book, not even

for tree level processes!

There are about 10 pages on path integrals and it is only in the context of quantum mechanics.

(And 3 of these pages are devoted to showing how to integrate x^n e^(-a x^2)!)

Some space is devoted to the electroweak theory and the Higgs mechanism, as well as a short chapter on

SUSY, but this is a strange choice of topics when there are such huge gaps in the sections on

quantum field theory, supposedly the main topic of the book. To learn quantum field theory, QFT Demystified

is useless, I am sorry to say.

Even the little material that is covered contains mistakes, and not just typos.

For example, he defines a group G as something obeying four axioms, one of which is

"Axiom 4. Order: The order of the group is the number of elements that belongs to G."

Obviously, this does not make sense as an axiom!

If you want a nice and pedagogical introduction to both quantum field theory and to

particle physics, save your money and get Griffiths' book (An Introduction to Elementary Particles) is infinitely better.

After Griffiths I woudl suggest any of the following books: Srednicki, Maggiore, Mandl and Shaw,

Aithchison and Hey, Halzen and Martin, Ryder, Peskin and Schroeder, Hatfield or Greiner, etc.

To conclude, if you know even a tiny bit about QFT, you won't learn anything new. If you have no background in QFT, you might feel that you have learned a little, but as soon as you look at other books or try to do a calculation, you will realize that the book did not teach you much.

When I was first trying to learn Quantum Field Theory (QFT), at the end of my college years and at the beginning of the graduate schools, the jump from the "regular" quantum mechanics seemed almost insurmountable. Even with a full year of graduate quantum mechanics, the kinds of concepts and calculations that are the staple of the QFT seemed beyond anything that I had encountered in Physics before. Unfortunately to this day there aren't many QFT textbooks that will give you the benefit of the doubt when first learning the subject. Most of them aim to be comprehensive, rather than pedagogical. Which is unfortunate because many more basic concepts and results are not beyond the ability of a more motivated undergraduate to grasp. In the light of that, I wish that David McMahon's book had been published earlier. There clearly is a need for book of this type, for both those who are interested in preparing themselves for a full-fledged course on QFT, as well for many practicing Physicist who could benefit from knowing the bare essentials of QFT for their own line of research (particle physicists, astrophysicists, etc.). As correctly pointed out by other reviewers, the book has its flaws. The ones that I find particularly prominent are 1. Many mistakes, 2. It can be conceptually fuzzy and less than accurate when it comes to some key concepts. 3. Non-inclusion of non-relativistic QFT (important for condensed matter applications) 4. Inclusion of Supersymmetry, which is a non-standard topic for most textbooks, and not even a verified concept, and 5. Poor typesetting. However, even with those flaws, the book is an important text for everyone who is interested in learning about QFT on their own for the first time. But it is not meant for everyone: one year of college-level quantum mechanics and familiarity with the modern tensor notation would be the minimal requirement s for taking a fool advantage of this book.

After reading this book, I am perhaps more mystified than before. I would at best regard this book as a primer to advanced quantum mechanics and a beginner's introduction to elementary particles. There is very little quantum field theory to be found. So, even neglecting the score or errata in the book, you will find that the author fails in his primary objective.

No, I was not expecting an intensive mathematical treatment with in-depth and rigorous derivations. I was expecting something along the lines of 'Relativity Demystified', which I thought served its purpose (even though that, too, is riddled with errata). For more in depth explanation of the specific problems, see the 1-star review of this book by Gen. He nailed my thoughts precisely. Avoid this book - even as a study guide.

I'm taking a module in QFT and I found it tough.But after reading this little book,it helps to unlock some of my brain-jam on the abstract concepts.The mathematical details are highlighted sequentially with clear explanations given.This book is really one of the gems among other QFT books.How I wish that all books in the world are written with such clarity!! Another wish is that hopefully the author can go on to write an in-depth advanced QFT textbook retaining the features found in "Quantum Field Theory Demystified"..That would indeed be great as a life-saver to all students struggling with understanding QFT.