Qft Definition and 956 Threads

Is one semester of quantum sufficient preparation for a QFT course?

The condition of microcausality (commuting fields for spatially separated points) can be shown to hold in the Fock representation in quantum field theory (see e.g. Peskin & Schroeder section 2.4). However, in algebraic quantum field theory the condition of microcausality is postulated as an...

I'm studying a QFT course, and we've been asked to consider why classical physicists found it useful to introduce electric and magnetic fields, but not fields for electrons or other particles. I'm completely stumped, and would appreciate any hints. thanks

Homework Statement In Zee's book on QFT, I'm confused on page 26 by how we gets from Eq (4) W(J) = - \int\int dx^0 dy^0 \int \frac{dk^0}{2\pi}e^{ik^0(x-y)^0}\int \frac{d^3k}{(2\pi)^3}\frac{e^{i\vec{k} \cdot(\vec{x}_1 - \vec{x}_2)}}{k^2 - m^2 + i\varepsilon} to Eq (5). W(J) = \left(...

[SOLVED] N+pi->N+pi exercise in QFT The due date of this exercise was several weeks ago, but I'm still struggling with this. Since some of the QFT exercises are kind of exercises, that are probably the same all over the world, I assumed there could be a non-zero probability that somebody...

i am having a big issue in deciding whether to read zee's qft in a nutshell book. peskin and schroeder's intro to qft, or ryder's qft book. I have heard the first chapter of zee's qft book is great but the other chapters get progressively worse because they are a general outline of the...

Homework Statement I don't understand how Zee gets Eq. (2) on p. 24: W(J) = - \frac{1}{2}\int \frac{d^4k}{(2\pi)^4} J(k)^\ast\frac{1}{k^2-m^2+i\varepsilon}J(k) Homework Equations W(J) := - \frac{1}{2}\int d^4x\int d^4y J(x)D(x-y)J(y) The Attempt at a Solution I don't see where the d^4k...

I'm looking for absolute basic but respectable introductions to QFT and GR. Any choices? What level of QM is recquired to learn QFT?

Homework Statement I'm trying to show that the general form of the propagator is D(x) = - \int \frac{d^3k}{(2\pi)^32\omega_k}[e^{-i(\omega_k t - \vec{k}\cdot\vec{x})}\theta(x^0) + e^{i(\omega_k - \vec{k}\cdot\vec{x})}\theta(-x^0)] but my answers always seem to differ by a sign. Homework...

Homework Statement I'm studying from Zee's QFT in a nutshell. On page 21, I don't understand how he uses integration by parts to get from Eq (14) to Eq (15), ie from Z = \int D \varphi e^{i \int d^4 x \{ \frac{1}{2}[(\partial \varphi)^2 - m^2 \varphi^2] + J\varphi \}} to Z = \int D \varphi...

Hi! Does anybody of you own the solutions of Mark Srednicki's Quantum Field Theory book? I work on my on this book. Thus it would be very helpful to have the solutions! Stilo

I have been wondering now for quite some time about the meaning of Euclidean Quantum Field Theory. The Wick rotation t\to it allows us to transform a QFT in Minkowski space to a QFT in Euclidean space (positive definite metric). After that the expectation values of observables can be...

Some friend asked me the following question: For a real scalar field \phi, assume that H = H_free - \int d^3 x\ J \phi. J(x, t) is just some real number, source, or background field, without second quantization. Now, what is the amplitude \psi(x, t) for finding a particle at time t(before...

If I understand correctly positions of particles cannot have exact values in QFT, there are no eigenvectors of position (right?). But the positions of particles must correspond approximately to some state in QFT because position is meaningful in QM and classical physics, and QFT is supposed to...

A few months ago I started a thread asking some basic questions about QFT and it led to a large number of posts that were extremely interesting and that I am still going through. But the thread started to go in several directions (all very interesting!) away from my initial basic questions...

I want to study 3 subjects on my own,the subjects are Group Theory, tensor analysis, and QFT. I know this might be a silly question, but regardless of what textbook material i have or how much I know, what is the best order to study these 3 subjects ? I feel I should leave QFT to the last...

We have the Lagrangian of EM field: L=-\frac{1}{4}F_{\mu\nu}F^{\mu\nu} Variation of Lagrangian give Maxwell's equations: \partial_{\mu} F^{\mu\nu}=0. or (g_{\mu\nu}\partial_{\mu}\partial^{\mu}-\partial_{\mu}\partial_{\nu})A^{\mu}=0. (equation 7.3, p.241) Ryder, then, claims that...

do you need to know about the propagation of light to understand quantum field theory? note: when i speak of propagation of light i am only talking about these topics only: geometrical optics, intensity, the angular eikonal, narro bundles of rays, image formation with broad bundles of rays...

[SOLVED] Ryder QFT 2nd ed. Page 192 Homework Statement equation 6.51. This equation is actually 2 equations separated by a comma. I don't understand either one and would appreciate any help to get me started. For the time being, I would like to concentrate on the first one...

Homework Statement I have edited Ryder's text to emphasize the issue I am having. The actual text is approx. 40% down from the top of the page. (\frac{2\alpha}{i})^{3/2}\int exp(\frac{i}{2\hbar}\mathbf{P\cdot x} + i\alpha \mathbf{x}^2)d\mathbf{x} The integral may be evaluated by appealing to...

Homework Statement The first expression in equation (4.4) is: \frac{d^4k}{(2\pi)^4}2\pi\delta(k^2 - m^2)\theta(k_0) Homework Equations Ryder is most ungenerous on this page. Some concepts, important to understanding the entire chapter are left unexplained. For instance, the reasoning...

I am wondering whether someone can suggest a good ref or two (preferrably with worked example) on how to use Cutkosky (or whatever it is called) cutting rules in QFT to help pick out the absorptive/Imaginary part of a 1- or 2-loops diagrams. I have already tried Peskin and Schroeder, which is...

Homework Statement (1 - \frac{i}{2}\mathbf{\sigma\cdot\theta})\mathbf{\sigma}(1 + \frac{i}{2}\mathbf{\sigma\cdot\theta}) = \mathbf{\sigma - \theta\times\sigma} Homework Equations The Attempt at a Solution At one point in this, I temporarily ignore the y and z components. I hope the notation is...

is Fourier analysis in qft just used for going from a position wavefunction to a wavefunction described by the wave vector (k)? also why is the integral divided by [2(pi)]^n where n is the number of dimensions and how do you know when to divide the integral by the 2(pi) factor or not?

Homework Statement There is an unnumbered equation in the top half of the page: (1 - i\mathbf{K\cdot\phi})(1 - iP\cdot a)(1 + i\mathbf{K\cdot\phi})(1 + iP\cdot a) = 1 + [P_{\mu},P_{\nu}]a^{\mu}a^{\nu} + 2[P_{\mu}, K_i]a^{\mu}\phi_i + [K_i,K_j]\phi_i\phi_j Homework Equations The...

Homework Statement On page 41 of Ryder's QFT, just below eqn (2.84), it says: \gamma = E/m I was unable to verify this, unless it is meant to be true only for small speeds. Homework Equations E = \pm(m^2c^4 + p^2c^2)^{1/2} (2.24) page 29, but as suggested n the book, we let c = 1, so E =...

Hello, I just reading and learning QFT and there is something I've been wondering, hopefully somebody here can help me. Let's say we have an interacting Quantum Field Theory, such as Quantum Electrodynamics if we want to compute an amplitude such as two electrons scattering off each other, then...

Hi all, I am wondering if anyone out there could give your recommendation as to what my first QFT book should be considering that I'm an experimentalist interested in particle physics. Having said that, obviously the goal is to quickly understand the "derivations" of Feynman rules and be...

i know these threads are common in this subforum so i apologize but what math should i know before picking up a qft book?

Does anybody knows a textbook, a paper or any lecture notes that discusses the \phi^3 interactive field? I use as main reference Ryder's QFT, which discusses only the \phi^4 interaction. And most similar textbooks (like Peskin's, Brown's etc.) do so. I have derived the point functions and...

Does anybody knows a textbook, a paper or any lecture notes that discusses the \phi^3 interactive field? I use as main reference Ryder's QFT, which discusses only the \phi^4 interaction. And most similar textbooks (like Peskin's, Brown's etc.) do so. I have derived the point functions and...

Hi all, I asked about this on the academic and career guidance forum but didn't get any useful replies. Which of these maths subjects (all at fourth year level) would you recommend for someone interested in the subjects listed in the title? What would you say is missing from this list...

Euler-Lagrange equations in QFT?? Hi, I have a problem with a Wikipedia entry::bugeye: http://en.wikipedia.org/wiki/Euler-Lagrange_equation The equations of motion in your quantized theory (2nd quantization) are d/dtF^=[F^,H^] i.e the quantized version of d/dtF={F,H}. My notation: F^ is the...

I'm only going to be a junior next year in high school so bear with me but I've been "studying" quantum mechanics and quantum field theory for a while now. I understand most of what I've read very well but there are a few things that have been bothering me. *How does QFT explain how two...

Hi, I have been wondering why we can consider d(phi)/dt when we are in Schrödinger picture (phi is just the usual scalar field here). Isn't this 0 as operators do not depend on time in this picture? However then how does it make sense to talk about the conjugate momentum in this picture which...

Hi guys, Everyone knows that one can calculate the S-Matrix with various tricks. One of them is to use traces to simplify the matrices. Can someone tell me or point me to a place where I can find an explanation why I can do this? I think I vaguely remember that I have seen once an...

I have some extremely basic questions in QFT. First, P&S discuss causality in QFT in the first chapter of the book and, after showing that <0| \phi(x)\phi(y)|0> does not vanish for spacelike intervals, they say "to really discuss causality, however, we should ask not whether particles can...

Hello, I just realized that I could not figure out how static fields can be handled in QFT. Although I realize that really static fields don't really need QFT, I nevertheless would like to see how QFT covers this extreme case. Maybe a limit for low frequencies would be useful. Have you...

Here's a blog entry from "An American Physics Student in England" http://fliptomato.wordpress.com/2006/12/30/from-griffiths-to-peskin-a-lit-review-for-beginners/

hi everyone, There are so many books about QFT, but what is in your oppinion the best book to learn quantum field theory?

I am confused about the relation between condensed matter physics and Quantum field theory (QFT). Here are my "naive" questions. 1. The condensed matter physics deals with the macroscopic physical properties of matter. The number of atoms of the system is as large as Avogadro's number. But in...

I'm interested in studying LOCAL theories within QM. I have the impression that the following theories claim to be such: MWI (Everett) RQM (Rovelli's Relational QM?) QFT (Originated by ?) LQM (There's a book titled ''Local QM'' as I recall.) + Questions: 1. Are there any other LOCAL...

\delta^{\left(d\right)}\left(\b{q}-\b{q}\prime \right) from Quantum Field theory and Critical Phenomena by Justin.. (the text covers QFT from a statistical view) Question: what does the d in brackets mean/do ? Thanks =)

hi, actually i am searching a good introduction into quantum field theory. the book should be like the lectures of feynman (The Feynman Lectures on Physics), i mean, not so mathematically as usually. thx for answering

Hi, I'm trying to teach myself QFT, and I'm stuck with one formula in Part I of Weinberg's trilogy. I think I managed to understand how one gets Formula 2.B.7 in the appendix of Chapter 2, thanks to the information provided by Weinberg, but don't get 2.B.10, page 97. Could anyone one give me a...

I'm reading some QFT and have been puzzled by the following question: What's the physical meaning of the position OPERATOR X_\mu in QFT? whose position does it measure?:confused: Thanks for any help.

Kea posted this on another thread: The Tomita-Takesaki results are and exciting breakthrough in AQFT, by now getting to be pretty well understood. The beginnings of it are in Haag's book Local Quantum Physics. Another line of work in AQFT that approaches the idea of matter in QG is...

I'd like to be as familiar with functional methods as with calculus. Otherwise I always fell not to grasp QFT comprehensively. Any help is much appreciated!

I'm still pretty new to QFT, so forgive me if I have made a ridiculous mistake. I've been learning QFT from Peskin and Schroeder mostly but decided to read Ryder recently and I have just come across an amazing result (in my opinion) in Chapter 3. Ryder basically shows that the electromagnetic...

Derivation of Poincare Invariance from general quantum field theory C.D. Froggatt, H.B. Nielsen Annalen der Physik, Volume 14, Issue 1-3 , Pages 115 - 147 (2005) Special Issue commemorating Albert Einstein Starting from a very general quantum field theory we seek to derive Poincare...