Qft Definition and 981 Threads

Hi, Today in QFT class, we examined an infinitesimal Lorentz transformation. From this we showed that a LT is represented by an anti-symmetric matrix. But this means that the diagonal elements should all be zeros. My question is how this reduces to the standard LT with gamma, gamma...

Hi, I have a question regarding normal ordering in QFT. I know that it moves dagger operators to the right and that it gets rid of infinite constants turning up and that 'with observables defined in normal products their vacuum expectations vanish.' (Mandl and Shaw) I have a couple...

Is string theory the (more-or-less) only way of dealing with 'extended bodies' in a theory like QFT? Or does it only deal with very specific actions, or ones representing 'particles' with special dimensionalities (e.g 1+1 only)? If it is general, is all the commonly-stated phenomenology (11...

How much is this renormalization business a problem in QFT? Always read it’s complete ‘hand-waving’ and arbitrary, but also that QFT is the most precise theory ever. Also found this quote: "[Renormalization is] just a stop-gap procedure. There must be some fundamental change in our ideas...

For some reason, I skimmed the wikipedia article on QFT, and I feel like I kind of have an idea what the basic objects are... it would be nice if I can be told if I'm way off base, or something close, or whatever. I'm trying to figure out just what the objects are first, and I'll worry about...

I'm a grad student. I've done 2 semester of QFT using Peskin but I've didn't too well due to many reasons. I now want to go back and catch up on things I should have learned better, and then learn even more - I want to be a good field theorist. I'd like to see if there's anyone in a similar...

Here is a paper on the arxiv, preprint of an encyclopedia entry, which might be useful to many to introduce the ideas and techniques used in perturbative quantization of different fields. If you are content to accept for the moment brief definitions instead of leisurely motivations of the...

I just finished an introduction to quantum mechanics class, and I was wondering where I could learn QFT on my own (including any more QM I might need to learn before I could start QFT). I have Griffiths book, and in class we covered the first 7 chapters (which includes all the basics...

Hi, I have a question: The EPR experiment told us the world is nonlocal. And as we know, the QFT is a local theory, there is a principle that measurement do not affect each other between spacelike points. Do the two conflict? And can we say "we can not find an experiment for now which does not...

The electromagnetic neutral pion decay is a three-point interaction: it decays into two virtual and charged Kaons or Protons, of which one then radiates a photon and then annihalates with the other to produce a second photon. (Obviously, a neutral particle cannot radiate photons directly)...

I have three questions about QFT. I know you can answer this questions, sure you can. - How does a standing wave look like in 3 dimensions (x,y,z). I mean an electro magnetic oscillation between two walls or in free space. I can't really imagine that thing and looked for pictures (google) but...

I was wondering, is there a possibillity that QFT with curved spacetime is a the path to unification? Also, what advances are there in constructing QFTs with dynamic spacetime? If this way is feasible, who are the people spearheading it?

Hi, I'm stuck with problem 10.3 from Peskin's QFT book. I'm trying to evaluate the 2-loop sunset diagram in massless phi^4 theory however I keep running into trouble. I'm trying to use standard feynman parameter + dimensional regularisation techniques however i keep getting stuck when it...

First off let me start by stating that I am aware that you must get a great amount of "snake-oil theories" on this board and that I have no interests in "peddling". I am merely a high-school student, very interested in physics, who was lucky enough to stumble across these forums. I had an idea...

thanks for advices.

I want to read papers about the QCD and superstrings, which books are better to read firstly as an introduction.

Hi, I'm trying to work out the problems on peskin's book. Does anyone know that where I can find the solutions to them? It is really hard to do it all by myself. Thanks!

Hello, First I want to apologize for this FAQ-like question, but I couldn't find the answer anywhere here. so...I'm looking for a good book on quantum field theory and I'm new to this subject. I've had a introductory course on quantum mechanics. I found the following on the internet: -...

I just heard that the cosmological constant is a coupling constant in some perturbative expansion of some QFT and can be interpreted as a mass? Is this true? Wouldn't that be interesting? That would mean that the GR effect of expansion may be responsible (or may be an equivalent expression for)...

I am unsure if this is the proper forum for this, since it is not actually homework... but here goes anyway. I am trying to Prove Peskin and Schroeder equation 2.33( the second equal sign) P=-\int d^3 x \pi (x) \nabla \phi (x) = \int \frac{d^3 x}{(2 \pi)^3} p a^{\dagger}_p a_p so...

I've sometimes heard that there are string theory results that are quite similar to some of non-commutative qft. What are these?

Can anyone give me an explanation in layman-terms of the concept of a Polyakov-loop in QFT? What does it mean fysically. I know that this is often used in lattice QCD, but why ? I have the same questions for a socalled Ward-identity regards marlon

Hello all, I'm reading through this book now and I'd like to know if there are other people who are also doing so, have read it or are planning to read it in order to have a discussion about it. In fact, I've read before about the first half (a bit more) of Peskin and Schroeder and I think...

What is a Path in QM and QFT ? In classical mechanics, we are allowed to talk about path of a particle. But in quantum mechanics, the concept of path of a particle cannot be defined. This is due to the uncertainty principle. But Feynman talked about path integral in quantum mechanics. This...

Hello all, Just wondering if Peskin and Schroeder is a good first time QFT book? If so, what would be a good book to supplement it with? Cheers, Norm

Hello everyone, I am now learning QFT, this theory is really abstract and daunting. I can't understand the concept of vector field. What is vector field at last? why there are four polarization vectors? I feel that the whole theory is somewhat lack of reasoning, the postulates and assumptions...

What is quantum field theory and why was it developed? What is its relation to quantum mechanics?

Hi. I am new to this discussion group, so forgive me if this is not the appropriate forum for this question. A friend of mine and I are going through the first volume of Weinberg's QFT trilogy. My question regards the first problem at the end of chapter two. I think I completely understand the...

In critical phenomena, we can enlarge the block size(momenta fluctuation) by Kadanoff transformation, say k \rightarrow bk (b<=1) , and scale the new Hamiltonian by k' = k/b, x'=bx to recover to the original block size. In QFT, similarly integrating out the high momenta produces the effective...

I am interested in the input from the physics community on quantum field theory. If each particle has an associated field of which they are manisfestations what causes a particle to arise from a field?

Jeff mentioned he thought a thread on this might be good, and I decided to start it here so the board wouldn't be entirely blue sky. I'll start with a question raised by Patrick van Esch on s.p.r. In the Peskin and Schroeder textbook, they develop the expansion of the wave &phi; in the free...