Quantum field theory Definition and 558 Threads

Recently i am reading A.Zee's Quantum Field Theory in a Nutshell 2nd Edition. there is a equation that i can not derive by myself. I suspect its correctness. <k1k2|exp(-iHT)|k3k4>=<k1k2|exp(i∫dxL(x))|k3k4>, where the L(x) on the RHS is an operator function of space-time. This equation...

Hello Everyone! I have a problem I am solving through a self study project from Lowell Brown's book entitled: Quantum Field Theory". It is a math question (basically) on recursion relations. Homework Statement The variational definition gives us the relation: det[1-λK] = exp{tr...

Personally, I am interested in Topological Quantum Field Theory. And now I am battling against Quantum Field Theory. I am not sure how much Quantum Field Theory is needed to do Topological Quantum Field Theory. And I am not sure what should be the mathematical pre-requisites of Topological...

Now, I must preface this by saying that my understanding of QFT is limited, and my understanding of GR is even more so. Nevertheless, I was reading about the No Hair Theorem, and it seemed to me to be suggestive of the indiscernibility of Quantum Particles. Obviously, for a macroscopic black...

Wave functions and their exp(-ipx) are base of quantum mechanics and QFT. But how to derive them the most simply that we will understand why they are base of QM? It is interesting that Feynman in his book "QED: The Strange Theory of Light and Matter" very simplifies QED, but he did not give a...

In quantum field theory do we "describe" static electric fields with proper combinations of transvers propagating photons? Is that a basis? Is there a basis using the longitudinal and timelike photons to describe static fields? Thanks for any help!

I am struggling with equation 1.5 in Tong's QFT course. I try to understand/explain it in strict calculus, i.e. without physics shortcuts like "small variations". I guess in the full blown explanation, \delta S is a total derivative. To be specific, with total derivative I mean the linear map...

1. I read that the picture of gauge bosons as mediators of interaction originates in and is valid in perturbation theory. But how do we know that picture is correct? We do perturbation theory only because we do not know how to study a system in a fully non-perturbative way. If someday we...

The following statements are from the paper with the above title, recommended in another thread, are from here: http://fds.oup.com/www.oup.co.uk/pdf/0-19-922719-5.pdf An interpretion of these statements would be appreciated: 1. [first paragraph, page 3] What is 'conservation of...

I'm an undergraduate with interest in theoretical particle physics. No course available in QFT. I have background in particle physics, quantum physics and relativity. Want to start learning it before going for M.Sc I've seen books like Mandl and Shaw, Landau and Lifgarbagez in university...

In some class notes I found those conditions interpreted as a "five requirements on Hamiltonian of physical system": 1. Unitarity -> Hamiltonian has to be hermitian operator 2. Claster decomposition (microcausality and locality) -> (? missing part) 3. Poincare invariance -> Hamiltonian...

when a continuous symmetry is broken, we say that the ground state is just one of the possible ground states, and there is no energy cost in moving from one to the other.. why doesn't the state keep changing with the slightest perturbation (production of goldstone boson). why don't we have a...

I'm a grad student in math, and I've been trying to learn some physics on the side by taking some classes and reading books. I took a class on quantum field theory last semester that was taught out of Srednicki; the class was very good, but I found myself at the end with a conceptual question...

Hello everyone! I want to study QFT and I want to know all of the required mathematics for it. I know most of quantum mechanics topics -wave function -schrodinger equation -state, operator -perturbation theory I know some of special relativity. And I almost familiar with einstein's...

I have a question concerning the notion of electric charge in QFT. What value of charge for electron should I use if I want to compute the force acting on electron in some external electric field. Of course in first approximation it is just elementary charge which value might be found in...

What does it mean if something "Transforms Covariantly"? (Quantum Field Theory) Referring to an isospinor, \psi which transforms as \psi(x)→ \psi'(x)=S(x) \psi(x) (S(x) being an n by n matrix) I'm told that it is clear that ∂_{μ}\psi does not transform covariantly. Now, correct me if I'm...

What is the relationship between quantum field theory and string theory?

Hi, My question is about why quantum fields are used. Are quantum fields just a reinvention of the ether? It seems like something superimposed on spacetime (from which theoretically spacetime should emerge in the case of gravity) from which particles can pop in and out of. How wrong is...

Hi, I'd like to ask recommendation for a QFT book. I have seen several other recommendations on this forum, but hopefully I'll provide enough info so you guys can have more specific advice. Background: QM (Griffiths, some parts of Sakurai), GR (Carroll), some residue...

"virtual particles" in rigorous quantum field theory If I am not mistaken "virtual particles" are just a name someone put to some integrals that we use to calculate different things, and those integrals depends on the perturbation scheme and on the gauge selected, and they don't even exist in...

Consider q3 in this exam: http://www.maths.cam.ac.uk/postgrad/mathiii/pastpapers/2006/Paper48.pdf I reckon I can manage a good part of the rest of the question. Unfortunately, I cannot manage the very first bit (drawing the Feynman diagram) and this is preventing me from continuing! I...

We have the effective action which obeys \frac{\delta \Gamma[\varphi]}{\delta \varphi(x)}=J(x) where and we are told the stationary point, \varphi_0, of this action, \frac{\delta \Gamma[\varphi_0]}{\delta \varphi(x)}=0, corresponds to the vacuum expectation value. (This is out of my notes -...

Hi there! I'm attending an introduction to elementary particle physics and I came into this statement about the Dirac equation: "When an interaction is added (using the gauge principle) in a field theory, then some terms appear like: gBj where, g is the coupling constants, B is a bosonic...

Sometimes I find useful and more interesting to read a less rigorous textbook before tackling a reference textbook of a given subject. Having said that, I am looking for a book that introduces the ideas of quantum field theory in a relaxed way. This allows to grab the ideas and then formalize...

Pls. answer in the simplest and the most intuitive way. 1. What is the reason our quantum field theory needs perturbative approach. Is it because in the concept of fields, there is an infinite number of freedom in the oscillations of the virtual particles, or is it because the field is...

It's not a requirement at my school's Physics PhD program (it's a graduate-level pass/fail course), so I'm curious as to whether or not other schools have the requirement, and how many students ultimately opt to take it.

From a previous post, I now know that the 'qualities' of QM such as entanglement, superposition of states, decoherence, measurement problem, are still with us in QFT. 1. Is the Dirac equation the primary equation in QFT? 2. What equation governs the evolution of a macroscopic object in QFT...

Please teach me this: Why we do not call the quantum field theory the quantum mechanics of a changeable number particles.Why we must use the term ''field''.I think that the indistinguish of identical particles,the dual particle-wave and changeable in number of particles mean the ''expansion''...

Steven Weinberg wrote: ''In its mature form, the idea of quantum field theory is that quantum fields are the basic ingredients of the universe, and particles are just bundles of energy and momentum of the fields.'' (see p.2 of his essay, ''What is Quantum Field Theory, and What Did We Think It...

Mark Srednicki's "Quantum Field Theory" I just wanted to know what level the book QFT by Mark Srednicki is, that is... Is it considered first year Masters, second year masters... Low PhD..?? I know it's not upper year undergrad, that's for sure. Just wondering. thanks!

Quantum Field Theory Purly in Momentum Space? Hello, I have a complicated nonlinear-nonlocal-nonrelativistic-effective action in momentum space and would like to do perturbation theory with that. I need to find propagator and Feynman rules. I can not go to x-space and follow the standard...

I'm trying to understand path integrals as described in my lecture notes (which are reinforced by Peskin &Schroeder). Anyway on p284 of P&S, there is a formula inbetween eqns (9.17) and (9.18) that reads: e^{-iHT} | \phi_a \rangle = \sum_n e^{-i E_n T} | n \rangle \langle n | \phi_a \rangle...

Please teach me this: Can we demontrate the convergence of perturbation series of quantum field theory(Feymann diagrams) after making the renormalizing procedure? If we can't demontrate that,why we still consider the perturbative method using in quantum field theory being useful and believable...

Dear all, I am taking 'field theory' course this semster and I am reading 'quantum field theory' by mandl and shaw. In chapter 8, equation (8.9) we see: E_1 E_2 v_rel=〖[(p_1 p_2 )^2-m_1^2 m_2^2]〗^(1/2) and we know that as p is a four vector: p=(E,P)=m so p_1 p_2 = m_1 m_2 ! Isn't...

What is a good to book to start reading about quantum field theory?

I wish to learn quantum field theory? Where should I start? I do know something about Dirac's bra-kets and elementary QM.

Does anyone know why in quantum field theory mass terms are quadratic in fields (not contaning derivatives)? Thanks!

Hi I am looking for a book or pdf where I can read more about quantum field theory. How to renormalize and find the counterterms. thanks alot

Hi guys, Before responding to my post, please note that I am only familiar with the mathematics of nonrelativistic quantum mechanics, and don't know any quantum field theory. All I have is this vague idea that quantum field theory is the union of special relativity and quantum mechanics...

what is the analogue of 'space is curved' in Quantum Field theory ?? if in General Relativity the main issue is that 'space is curved' what is the equivalence of it in Quantum mechanics ?? , for example how can QFT describe the curvature of space ??

Does anyone know of quantum field theory lecture videos besides susskind and coleman.

can zeta regularization provide FINITENESS to quantum field theory ?? recently i came across (google) these papers http://vixra.org/abs/1003.0235 http://vixra.org/abs/1001.0042 http://vixra.org/abs/1001.0039 using the zeta regularization algorithm plus analytic continuation he...

I have pretty good handle on non-relativistic quantum mechanics, but I would like to learn about the Standard Model (Quantum Field Theory). What is the best introductory book and/or introductory article on QFT? Thanks Here are some I've heard of: Articles "[URL Model: An Introduction Authors...

The in the preface to his quantum field theory book, Srednicki mentions that there is a set of lectures by Ed Witten on quantum field theory for mathematicians that is available online. Does anyone know where this is?

Quantum Field Theory -- variational principle In non-relativistic quantum mechanics, the ground state energy (and wavefunction) can be found via the variational principle, where you take a function of the n particle positions and try to minimize the expectation value of that function with the...

This may be a very basic question, but I've had now some background on the quantum theory, and I think I am missing something. Roughly speaking, I feel like the main difference is that quantizing involves going from field amplitudes to counting operators, implying that a quantum process involves...

At least one of us at this discussion board has expressed an interest in fractal modeling of spacetime, or of dynamics.* This paper by Calcagni may be suggestive of what form such an approach could take. http://arxiv.org/abs/1001.0571 Quantum field theory, gravity and cosmology in a fractal...

Research in relativistic quantum mechanics proves, through a series of no-go theorems, that localized three (or four) dimensional particles cannot be the basic elements of reality. It is claimed that a field ontology can explain the appearance of three dimensional particles, but this new idea...

Hi there, I am currently studying Quantum Field Theory (well, for about 3 weeks isch), and it's really interesting and good fun! However, I would like to know how QFT relates Integrable QFT... I don't really know what it is. Can anyone tell me (i) The theoretical background of Integrable...

Hi there, I am currently studying Quantum Field Theory (well, for about 3 weeks isch), and it's really good fun! I would like to know how QFT relates Integrable QFT... I don't really know what it is. Can anyone tell me (i) The theoretical background of Integrable QFT (ii) The...