Qft Definition and 956 Threads

Hello, I'm thinking of starting to study some QFT. I know EM and QM on the level of the first part of Griffiths' books on the subject, and I know (classical) mechanics on the level of Marion & Thornton/Taylor, and I know GR on the level of Schutz/Hartle. Are there a few topics in these areas...

solving for commutator in QFT I am just starting to learn quantum field theory. I'm still an undergraduate but I love particle physics and I want to get ahead, so I got the book "introduction to quantum field theory by peskin and schroeder" I got to page 21 and I'm already stuck at an integral...

After recently researching about Quantum Field Theory and more specifically gravitons, I am slightly confused with how this theory of the gravitational force fits in with general relativity. I know it hasn't disproved it so there must be some connection. Do gravitons in 11 dimensions cause...

By looking at some physical formula and noticing various symbols like c and hbar, one can immediately say that the formula in question describes relativistic / quantum effects and not classical. What about QFT? Is there any way one can, only by looking at the formula, say that it's a product of...

In Peskin and Schroeder, we calculate that the propagator D(x-y)=\langle 0|\phi(x)\phi(y)|0\rangle to be non zero even if x and y are space-like separated (although it's exponentially decaying). This suggests (given our interpretation of this quantity) that a particle CAN propagate between these...

I learned QFT by reading Peskin & Schroeder, and now find myself unfamiliar with dimensional regularization of IR divergences which is prevalent in the literature. Are there good QFT books which discusses IR dim. reg.? I understand the general idea of going to more than 4 dimensions as opposed...

Hi, I'm trying to prove the Shouten identity for twistors: \langle pq\rangle\langle rs\rangle+\langle pr\rangle\langle sq\rangle+\langle ps\rangle\langle qr\rangle=0 It's easy to show that the LHS here is cyclically symmetric under q\to r\to s \to q, and also completely antisymmetric...

Please teach me this: Why the Lagrangian in QFT does not include high order derivative of field?Is it correct the reason being all fields obey the only Dirac and Klein-Gordon equations? Thank you very much for your kind helping.

Please teach me this: Why they say QM is a pillar of QFT?Is it correct it is because of the operator of field obeys the Dirac or Klein-Gordon equation of QM?Is the value of fields(not operator of fields) being the wave function in QM?I do not understand why we can consider QFT including QM...

Recently a student brought the following to my attention from Weinberg’s Quantum Theory of Fields, Volume I, from page 177, which I must admit that it stumped me. Here Weinberg introduces the concept of Cluster Decomposition: “It is one of the fundamental principles of physics (indeed, of all...

From Richard Feynman's Nobel Prize Speech. It must be clearly understood that in all this work, I was representing the conventional electrodynamics with retarded interaction, and not my half-advanced and half-retarded theory corresponding to (1). I merely use (1) to guess at forms. And, one...

So, first off, I'm thinking Lorentz invariant quantities are the same in any inertial frames S and S' regardless of their relative velocity. I'm thinking I need to show that \frac{d^3k}{(2\pi)^32E(\vec{k})} = \frac{d^3k'}{(2\pi)^32E'(\vec{k'})} where the primed & unprimed quantities denote...

Hi, i can't get the result stated as equation (2.33) in page 22. To be more clear, after the elimination of the divergent commutator, i still have two extra terms that i don't know how to cancel out. the total extra term is ap.a(-p)-a^+(-p).a^+p. :confused:

Please teach me this: Why perturbative QFT is still very useful theory?.Because perturbative QFT is asymptotic theory,so in many cases the series do not converge,then the error might be very large. Thank you very much for your kind helping.

Someone said at a conference today that there was no empirical support whatsoever for the idea that non-perturbative methods could be successfully applied in QFT. Does anyone know any counterexamples to this claim? I don't work in this area, but it sure doesn't sound right to me... Any...

I'm working through the start of the Quantum Field Theory book by Peskin and Schroeder. The first section deals with an electron and positron colliding to give a positive and negative muon traveling along a line at an angle theta to the line of the e,p collision.(This is using center of mass...

I am looking for books or papers that explain conceptual ideas that underlie the study of quantum fields. I am looking for something that clearly explains Field measurement. Most textbooks i am aware of emphasize on the development of formal techniques of Quantum field theory.

Hi, I have now finished University where I took an advanced quantum mechanics module in my final undergraduate year. Having left I was quite surprised to find out that this is infact only a grounding in the subject and I would like to know more. I have covered operators and the Hamiltonian...

I have read that, in QFT, unlike QM, there is no position probability density function because position is not considered an observable. Then how is a position measurement represented/modeled in QFT? As always, thanks in advance.

I'll be taking a first course in quantum field theory and general relativity this fall at the masters level and I have a few weeks until I start. I was wondering if anybody had some advice on what to brush up or even self-teach before I'm neck deep in them (on top of other classes) so I can be a...

Hello! Im trying to do QFT on my own and its going fine.. except one confusion now. We have our operator fields corresponding to our observables, and our state which is a function of space and time. But doing the second quantization we get the creation and destruction operators which now...

I like to plan ahead so as of now I basically have a good idea what my schedule will be like for all 4 year of college. I want to go into QFT eventually so I think the math classes I have decided to take will be best for that. They are Multivariable calculus( freshmen year 1st semester) Half a...

Hi, a few lines below equation (3.1.5) Weinberg writes: "The transformation rule (3.1.1) is only possible for particles that for one reason or another are not interacting." I thought a lot about it, but don't see any possible reason. Can you help please? After a few lines he defines...

Hi, guys. I will start learning Peskin's QFT from the coming fall semester. I plan to spend 2 years for studying in order to strike a thorough understanding of QFT. Peskin's QFT book in general is a good one, but it focus on calculation techniques; thus, I think I need a companion book which...

Hello everyone :) I'm reading the book QFT - L. H. Ryder, and I don't understand clearly what are the generating functional Z[J] and vacuum-to-vacuum boundary conditions? Help me, please >"<

Please teach me this: Why do they only consider S-matrix(or Green functions) in Quantum Field Theory?How about other physics observations as considering in normal Quantum Mechanics,e.g angular momentum...of particles?If we consider the other physical observations,how could we represent them in...

I am reading a nice book (Quarks and Leptons, by Halzen and Martin) about particle physics. It states that the general form of the propagator of a virtual particle is: \dfrac{i\sum_{\text{spins}}}{p^2 - m^2} I see that this is the case for the Dirac propagator...

I'd like to learn QFT on my own, what's the best text for that? Srednicki's? what do people think of QFT demystifyed? thanks

Eq. 9.124 has 3 steps. The first one gives 0 propagator for ε goes to 0. The final step, the one with Z gives infinity. Can anyone post the correct steps? Is there anything wrong in previews equations? It is important for me to learn the Ryder's book method. I have an exam in 10 days

Homework Statement The task is to show the invariance of a given Lagrangian (http://www.fysast.uu.se/~leupold/qft-2011/tasks.pdf" ), but my problem is just in one step (which i got from Peskin & Schröder, page 70) which i can not reproduce due to my lack of knowledge regarding spinors. The...

Homework Statement I'm working through the derivation of the Compton scattering crossection and I'm getting stuck partway through. More details below: Homework Equations The Attempt at a Solution So, I'm following along with Zee section II.8. We have two diagrams that contribute to order...

Hi PF I know that a goal of the current research in High Energy physics is to get a describtion of QFT in curved spacetime. I assume this has yet to be described fully, but how about plain quantum mechanics in curved spacetime? Has it yet been described? Schreiber

Hello! I'm quite familiar with non-realtivistic QM and particle phenomenology. What I do really miss is a text, which builds on the postulates of quantum mechanics and stresses the similarities and differences between "single particle" nonrelativistic QM and QFT. I want to read about...

Consider 2 entangled fermions. If the spin direction of one particle is measured, then the spin direction of the other is instantly determined, regardless of the distance between them. This is the famous EPR-type experiment in non-relativistic QM. This implies that time is absolute, in...

In Peskin and Schroder Book QFT: They used the term: "amputated connected graphs". Does amputated connected graph in Peskins's book is same as the irreducible graph in common sense? I think it is the same, please reply. thank you all!

I have three months before I begin grad school,, I have been studying from Mark Srendnicki's book its good but I'm not satisfied (because I jumped to QFT instead of studying things in between)... I found Colman's Lectures (http://www.physics.harvard.edu/about/Phys253.html) and Lecture notes and...

I completed my Physics undergrad studies a couple years ago, so I had forgotten a lot of what I learned. But since I plan to start grad school this fall, I have spent the past few months reviewing Griffith's QM and E&M, along with doing a little self-study of grad-level QM from Sakurai. However...

Could someone tell at what level the Quantum Field Theory appears in a typical physics coursework? Undergrad? Grad? Also, from my understanding, the first 1.5 years of grad work aim to prepare the student for preliminary exams on the knowledge of undergraduate physics. That said, how much of...

I'm looking for recommendations for QFT books written from a more math perspective. I'm looking for the usual intro topics, including the standard model, etc. Ideally, emphasis on geometry and understanding. Calculating scattering in gory detail isn't my goal. From this thread...

It is said that in QFT, "particles" are just momentum and energy of the field. Is this just a conjecture or modelling to solve certain problems like photons coming out from electrons as it lower energy states or create a solution to other problems, or is it 100% proven that there are really no...

I am curious if quantum field theory says anything about how much time it takes for an interaction, or particle creation and annihilation, to take place. For example if I have a high energy photon, and it strikes an atomic nucleus and you get pair production forming an electron and positron...

Dear all, a couple of months ago I've come across by following a link in these forums a website containing an introduction to QFT. The author is working on an introduction to this subject that contains everything the student must know to approach this topic without giving anything for granted...

Hi guys. So I just finished most of Griffith's Introduction to QM text (including the problems). I was wondering, is this text enough to delve into Srednicki's Quantum Field Theory text or should I also go through Shankar's Principles of QM? Relativity should not be an issue (I hope) as I have...

I have completed Quantum Core courses as well as GR and it seems there is something I am missing before taking QFT/QED courses. Is there another subject between?

I know that the full 2 point Green's function is given by G_2(p,-p)=\frac{i}{p^2+m^2} since this is exactly how we define the physical mass (it is taken to be the pole of G_2). So I know that's what the 2 point green's function should be - I just can't actually SHOW that it's equal to that...

Hi, I always seem to have a problem with my indices... \Lambda^{\mu}_{\;\;\nu}\Lambda_{\bar{\nu}}^{\;\;\mu}= \frac{\partial x'^{\nu}}{\partial x^{\mu}} \frac{\partial x_{\bar{\nu}}'}{\partial x_{\mu}} Now, the first term I'm relatively sure is right (first lambad corresponds to first of the...

Hi PF How does Quantum Field Theory differ from relativistic quantum mechanics? Ain't Quantum field theory just relativistic quantum mechanics or are there more to the subject? :) Thanks in advance \Schreiber

Homework Statement From Mandl and Shaw (exercise 4.5): Deduce the equations of motion for the fields: \psi_L(x)\equiv{1 \over 2} (1-\gamma_5)\psi(x) \psi_R(x)\equiv{1 \over 2} (1+\gamma_5)\psi(x) for non-vanishing mass, and show that they decouple in the limit m=0. Hence show that the...

I have a question regarding how you choose courses to take in graduate school, and the amount of freedom you have in choosing courses. I'm tentatively planning on applying for admissions to PhD programs for 2012, and I'm planning on applying to a mix of biophysics, medical physics, and high...

Hi all , I'm self Studying quantum field theory by reading textbooks and following the derivations of results carefully but never done any problem on my own . I can Understand Concepts and derivations but did not calculate anything on my own . Is it Possible for me to do research without that...