Field theory Definition and 554 Threads

Dear Forum, I would like to understand what the origin of spin 1/2 is. I read in Feynman's lectures that the origin is related to quantum field theory. I know nothing about quantum field theory. Is there an easy explanation? Thanks Cabrera

Hey everyone, I would like to first point out I am not a biology major in any way...I am a physics major, with a ever increasing interest in neuroscience. I am trying my best right now to find ways that I can incorporate my physics knowledge to the brain. Right now I am trying to...

Hi, I'm a masters student trying to apply DMFT to problems involving transport in strongly correlated systems. I have a cursory understanding of the physics behind the Hubbard model, which is to say, I have spent some time with it in a quantum many body theory course. However, I now want to...

Hi! I'm used to integrating over infinite spaces when working with QFT so far, but in an exercise I stumbled across a statement that \int_V d^3x e^{-i \vec x \cdot (\vec p - \vec p')} = V \delta_{\vec p \vec p'} It is clear that this is okay when p = p', but it does not seem to make sense...

Is Magnetic field conservative or non-conservative in nature, I have searched online regarding this, it seems to be a divided house, MIT professor Walter Lewin demonstrated that it is non-conservative using an experiment, but still many arent convinced with the way experiment was conducted...

I just entered graduate school. As an undergraduate I took a graduate course in Quantum Mechanics, mostly for fun and practice because I knew the credits wouldn't transfer to the uni I was applying to for grad school. So, I got accepted there and even though the credit wasn't transferred the...

I'm a computer science and engineering student, who has recently developed interest about quantum computers. I can understand that quantum computers are totally linked with quantum mechanics. But I would like to learn whether there is any relation between quantum computing and quantum field...

I plan to study from Peskin and Schroeders book if it helps, I just need to know what topics I need to study and it would be greatly appreciated if someone could tell me what books are good on the subject, I have a limited budget however and if I could get a single or only 2 or 3 books covering...

We would like both 4-momentum and angular momentum to be conserved in a field theory such as QED. My understanding is that in the case of 4-momentum, there are two different descriptions of the same theory. (1) We can impose conservation of 4-momentum p at each vertex, which requires that...

In field theory: [H,P]=0 So shouldn't that mean there can be no scattering? If you have momentum state |p1p2> then it is an eigenvalue of P with eigenvalue p1+p2. But it should be a simultaneous eigenstate of H too, so e^(-iHt)|p1p2>= |p1p2> up to a phase factor. But in general...

Hello, I have to give a presentation on an application of electromagnetic field theory of my choosing, and I was wondering if anyone had any suggestions that might be more interesting than the ones that have been suggested. It's for a 2nd year university level physics (E&M) course, so the...

The weak force was not discovered until 1953 or thereabouts so that pretty much made Einstein's attempt to unify all forces an impossible task. Does anyone know how much time he wasted on trying to find a unified field theory? Other than write a paper on gravitational lensing and the EPR paradox...

If some one could please explain what a field is in as much detail as possible please. don't be shy I love a challenge. My understanding is that a field is a precise area surrounding its source. depending on the field you get different effects. For example with the higgs field, the higgs...

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...

Ginsparg "Applied Conformal Field Theory" I have some questions concerning the first two chapters of Ginsparg's text on CFT, which can be found here 1. In equation (2.1) primary fields of conformal weight (h,\overline{h}) are introduced as fields that transform the following way...

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...

Homework Statement Evaluate \lim_{z \to 0}:e^{ik \cdot X(z)}:|0\rangle where X(z) is a free chiral scalar field in the complex plane. Homework Equations In Conformal Field Theory, the free chiral scalar field in the complex plane is given by: \begin{array}{rcl} X(z) &=& \frac{1}{2}q -...

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...

Homework Statement I understand the premise of Noether's theorem, and I've read over it in as many online lectures as I can find as well as in An Introduction to Quantum Field Theory; Peskin, Schroeder but I can't seem to figure out how to actually calculate it. I feel like I'm missing 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...

I previously took part in two separate threads where I slowly went through various field theories from a rigorous perspective. I would like to restart the discussion. Here are the two previous threads for anybody who would like to take part this time: Thread 1 The pages from 12 on (and...

I have just read my first course on Quantum Field Theory (QFT) and have followed the book by Srednicki. I have peeked a bit in the books by Peskin & Schroeder and Ryder also but mostly Srednicki as this was the main course book. Now, I have to do a project in a topic not covered in the course...

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...

just looking at the standard model, which describes a host of fundamental particles and bosons, one could assume that the SM is a particle model. however, most of what i read appears to indicate that particles are merely "excitations" or manifestations of a field, and it has been stated on this...

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 am taking a course in Electromagnetic Fields Theory, and the prescribed book for us is Engineering Electromagnetics by William Hayt. We are referring to its 7th edition, in one numerical Example 2.3 we have to find total charge contained in 2 cm length electron beam where as we are given the...

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...

PREAMBLE: I'm not asking you to do this for me, just point me to some CLEAR references. THE PROBLEM: I am trying to understand the differences between Action-at-a-distance (AAAD) and Field theory. I am trying to better understand relativistic dynamics and the relativistic 2-body problem...

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...

I have a theory described by a 2-component field \psi_i (i'm working with BCS in Nambu-Gorkov representation, but any other field theory would be ok, that's why I'm posting in this subforum), and the lagrangian it's defined in the following way: \mathscr{L}=\psi^\dagger \Gamma \psi where...

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...

Hi All, I don't know whether to post this in quantum field theory or in cosmology. Maybe this stuff is one subject, not two. Hajdukovic published some papers recently which seem very intriguing even to an amateur like me who doesn't understand it. Here's the latest one...

My first question: QED has U(1) symmetry. The transformation is a function of x (psi -> psi*theta(x)). How does this depend on the spacetime? Do interactions therefore differ between curved space and flat space? Is this what leads on to QFT on curved spacetime research? My second question...

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...

My question is, is it still widely believed that an all encompassing "theory of everything" exists for the universe? It seems to me that due to quantum mechanics it would be impossible to actually observe enough data to predict precisely the behavior of quarks and other subatomic particles, one...

Does Quantum Field Theory and General Relativity Theory predict anything which is mutually exclusive? This question came up to me as i was thinking about why there was/is apparent rivalry/debate between the proponents of these two theories. As far as i understood, Universe(or Multiverse) is...

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

Hi, Can anyone explain why in field theory we require [f*(x),f(y)] = 0 for space-lkie intervals x,y; but not <0|f*(x)f(y)|0> = 0? Thanks!

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...

Hey everyone, I posted this a while back in General Physics without any reply, and it looks like this is actually the germane forum (despite the fact that I'm explicitly NOT looking for QFT) -- but I couldn't find the "move thread" option... Anyway: I'm looking for some books that...

Hey everyone, I'm looking for some books that really dig into the topic of classical field theory -- and not necessarily just the fields that were known during the heyday of classical physics (electromagnetic / gravitational), but not necessarily all about Yang-Mills and Dirac fields, either...

Hey fellas am having some trouble understanding the concept behind a rotating magnetic field. Looked up the wiki entry and a couple of other webpages, but only ended up getting more confused. I am well versed with all EM fundamentals, but still...:confused: OK so in a basic alternator, we...

Hi there PF I just want to ask, what are the main ideas behind Group Field Theory? How does it work, and what is the formalism? And why is it called GROUP Field Theory? :) \Schreiber

Sorry this is largely chemistry based, but delves into electron theory. I'm a little confused about how the colour of transition metal compounds arises. I understand that say for [Cu(H2O)6]2+, you have an octahedral arrangement around the central atom, and the specific positioning of these...