Quantum field theory Definition and 587 Threads

Homework Statement I was following this book "problem book in quantum field theory by voja radovanovic" and I got stuck in the following problem Prove...

The title says it all. I'm sorry if you get annoyed because of my "noobishness", but I'm still a physicist in training (taking undergrad Classical Mechs). I'm really interested in Quantum Theory and I keep hearing about Quantum Field Theory, but not a single website accurately explains what it...

The new geometric version of quantum field theory could also facilitate the search for a theory of quantum gravity that would seamlessly connect the large- and small-scale pictures of the universe https://www.simonsfoundation.org/quanta/20130917-a-jewel-at-the-heart-of-quantum-physics/ I...

What kind of background do I need to study many-body quantum field theory?

In QFT, which have infinite degree of freedom, there exlst infinite unitary nonequvilent representation. Expecially after phase transition, the two representation are unitary nonequvilent. So can we say that unitary are broken in QFT? Or a pure state can evolved to a mixed state which is a...

Hi, I am studying Peskin's An Introduction To Quantum Field Theory. On the beginning of page 284, the authors say We can turn the field \phi_S(x_1)|\phi_1\rangle=\phi_1(x_1)|\phi_1\rangle. I tried hard to prove this relation but still can't get it right. Could anyone give me some hints? Thanks.

Hey all, I'm not sure if this belonged in the physics or engineering forum, but here's the question: has quantum field theory been applied to any engineering disciplines yet? I know quantum mechanics has been used extensively in electrical engineering and materials science/engineering. I also...

Author: Robert D. Klauber Title: Student Friendly Quantum Field Theory Amazon Link: https://www.amazon.com/dp/0984513922/?tag=pfamazon01-20 (submitted by elfmotat)

We usually talk about good books, but we rarely talk about bad books. And that is good. But sometimes, we find that some book is so bad, so really bad, that we strongly want to tell this to the others. So I open this thread to inform others about science books which you find so bad that it...

In special relativity we have the relation that for a free particle E^2 = \vec p^2 + m_0^2 and that also hold in relativistic free field theories (free Klein-Gordon etc) where one can show that we have a completeness relation 1 = \int \frac{d^3 \vec p}{(2\pi)^3} \frac{1}{2E_{\vec...

Hi! I'm in a master course in theoretical physics and enjoying a lot to learn about Quantum Field Theory (QFT)! So I was thinking doing a PhD related do QFT. What are the best places to work on QFT? Thanks a lot!

A circularly polarized electromagnetic wave can be thought of proper combinations of orthogonal linear polarized waves, and a linear polarized wave can be thought of proper combinations of left and right circularly polarized waves. It seems one type of wave is no more fundamental then the other...

First of all sorry for my off-topic question here. I'm a computer science student, who has a high interest in mathematics (especially algebraic geometry), and physics (especially quantum mechanics, quantum field theory). For this semester I'm supposed to create to applications, from which one of...

Author: Michele Maggiore Title: A Modern Introduction to Quantum Field Theory Amazon Link: https://www.amazon.com/dp/0198520743/?tag=pfamazon01-20

Author: A. Zee Title: Quantum Field Theory in a Nutshell Amazon Link: https://www.amazon.com/dp/0691140340/?tag=pfamazon01-20

Author: Michael E. Peskin (Author), Dan V. Schroeder (Author) Title: An Introduction to Quantum Field Theory Amazon Link: https://www.amazon.com/dp/0201503972/?tag=pfamazon01-20 Prerequisities: Contents:

I need to derive the euler-lagrange equations for the following non-local lagrangian density for a complex scalar field ψ \mathcal{L} = \partial_{\mu}\psi^* \partial_{\mu}\psi - \lambda \int dy\, f(x,y) \psi^*(y) \psi(y) where λ is the coupling constant, f is a certain real-positive valued...

I haven't taken a course in qft yet, just looking ahead to see what's to come, and so far things are not looking good, I read the firet few chapters of qft in a nutshell, and jesus christ what is this stuff, where are the postulates? The equations of motion? How do I even do these crazy path...

Can you suggest any source available on internet which may be particularly helpful for those studying/brushing up knowledge of classical or quantum field theory without help of any teacher or friend? Some calculations are at first not so straightforward and there are many types of calculations...

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...

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...

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...

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...

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...

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, 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...