Field theory Definition and 523 Threads

I have a theoretical question. When doing canonical quantization, and writing the equation for he time evolution of operator in Heisenberg picture, we make use of the statement that the external potential commutes with the field variables [V(\phi), \phi] = 0 This is obviously true if...

http://arxiv.org/abs/0905.3772 Group field theory renormalization - the 3d case: power counting of divergences Laurent Freidel, Razvan Gurau, Daniele Oriti "A 3D GFT graph G is a fat graph" http://arxiv.org/abs/hep-th/9306153 2D Gravity and Random Matrices P. Di Francesco, P. Ginsparg...

i need references on the topics. thanx

I don't understand the physical meaning of one of my dimensions/variables. Let there be a gravitational potential \phi (x_a), a=1,2,3. Equation of motions of a freely falling particle is: \frac{d^2 x_a}{d t} = - \frac{\partial \phi}{\partial x_a}. If there are 2 particles falling, family of...

I'm interested in reading Feynman's calculation for the perihelion advance of mercury that used quantum field theory calculations of graviton interactions. Anyone know where it's published or a good source on the web? Of course I've googled physics forums and haven't found an answer.

I have a few questions about this. My understanding is this: In the canonical approach to QFT there is an ambiguity in the order in which we write operators when calculating matrix elements. The different choices just correspond to different vacuum energies, which we are free to ignore since...

Hello Anyone got some introductory notes / books on Conformal Field Theory for someone who know Quantum Field Theory at the level of Peskin's book? cheers

I'm not sure if this is the right place for this question, so feel free to move it. Anyway, my question is, is there any good reason why the following field theory should be Weyl invariant in an arbitrary dimension d>1: S = \int d^d x \sqrt{g} \left( g^{\mu \nu} \partial_\mu \phi \partial_\nu...

What are some good books for non physicists on quantum field theory?

What is group field theory, and its relation LQG, CDT? There's no wiki article on gft. I am aware of the numerous articles on arix, could someone summarize what these articles mean?

For free quantum fields, there are two types of observables indexed by wave-number, \tilde{\hat{\phi}}(k), the Fourier transform of the local field, which can be written as a(-k)+a^\dagger(k), and projection operators such as a(k)^\dagger\left|0\right>\left<0\right|a(k), a(k_1)^\dagger...

Please let me know what lecture I have to previously take. I already took undergraduate level lecture of quantum mechanics and mathematical physics. And I also want to know that perturbation and scattering theory is hardly important on studying QFT..I'm so worry about that I didn't study...

Can anyone tell me if this is the basic concept behind effective field theories: 1) You begin with your original Lagrangian, and you want to construct an effective Lagrangian out of it. 2) You redefine your coupling constants in your original Lagrangian so that they include the integral...

Hi all, I bought a book recently of this title. I wanted this one to compliment the field theory book I have already (Peskin and Schroeder) because I find the latter a little hard to follow on my own (I am currently taking Relativistic Quantum Mechanics and will be taking QFT course at some...

I have a fairly good background in mathematics (algebra, analysis, topology, differential geometry)... and a good physics background (till QM, general relativity). I am looking to study Quantum Field Theory on my own. I do not intend to master QFT completely and all its techniques, but want to...

Sifting through ArXiv and other sources, I've found many documents on the topic of String Field Theory, perhaps the most extensive being by Thorn, 1989*. This brings up the question: Will String Field Theory evolve in popularity and perhaps outshine the more traditional String Theories? With...

I have a question about an equation in Maggiore's Modern Introd. to Quantum Field Theory p.52: \delta x^\mu = w^\mu_\nu x^\mu = \sum_{\rho < \sigma} A^\mu_{(\rho \sigma)} w^{\rho \sigma} where the A is defined as A^\mu_{(\rho \sigma)}=\delta^{\mu}_{\rho}x_\sigma - \delta^\mu_\sigma x_\rho...

Does anyone know if M-Theory is that same as Superstring Field Theory?

Hi everyone, This is my first post and I hope to get some better understanding of something that has been bugging me. I understand (global) gauge invariance in the sense that |\psi\rangle denotes the same (physical) state as e^{i\varphi}|\psi\rangle, or more generally, the physical state...

In quantum field theory a field is described by a multiparticles state? And, a single particle is itself a field?

Hi there people. Just wanted to bring up the idea of unified field theory and see what you think about it and so forth... create a dialogue or even a tryalogue. Is it or is it not the general crown jewels of science to find a theory that can be applied to any system and therefore predict...

I'm not sure if this post should go here or into the quantum physics forum, but I figure this can't be a bad place to put it. I have a few questions about canonical quantization and quantum field theories with interactions that I hope someone can answer. 1. I've been told that in Klein-Gordon...

Hello! I've some problems understanding why in field theory a term (appearing in a Lagrangian) like \propto \phi^{2} is called "mass"-term (whereas \phi denotes a real field). Is there any interpretation? And is this a general expression for a mass term or could it be of any other shape...

Hi all, I've recently been reading about string field theory (note: I'm a novice). As I understand, the string field is an infinite collection of classical fields. But I'm uncertain as to why this formulation leads to background independence? Thanks all.

http://fisica.ufmt.br/school2/ Some of the invited speakers: Paul Davies, Abhay Ashtekar, Lawrence M. Krauss, James B. Hartle (to be confirmed), etc.

at crystal field stabilization in strong field case d4 CFSE=-16Dq+p d5 CFSE=-20Dq+2p d6 CFSE=-24Dq+2p d7 CFSE=-18Dq+p d8 CFSE=-12Dq it was shuld be +3P and +4 P why it be +p,2p,2p,p ?

Homework Statement Find the commutators [P^\sigma,J^{\mu \nu}] The answer is part of the Poincare algebra [P^\sigma,J^{\mu \nu}]=i(g^{\mu \sigma}P^\nu-g^{\nu \sigma}P^\mu) If someone can convince me that \partial_i T^{0\mu} = 0, (i.e. the energy-momentum tensor has no explicit spatial...

I will be starting a Masters degree in physics next year - 30% of the assessment will be a thesis (review, not research). I have selected CFT as a topic and my future advisor has pointed me to Francesco's 'Conformal Field Theory' as the book to use. Francesco's book is very good but I am...

Hi all, I have a question about the formulation of quantum field theories in curved spacetime. I'm still learning, and so I might not articulate this very well, but I'm wondering: If a region of spacetime can warp and curve, dynamically changing its shape in response to changes in energy...

I'm now in my fourth year of physics and taking QFT right now. I always was quite OK gradewise at my german university, had a 1 (=A) in my pre-diploma, was among the best, and thought I can do what I want to do, which is fundamental physics. Right now I'm in the USA. Every teacher I had was...

Hello Physics Forum I will be taking a quantum field theory course next semester. I bought Mandl's book and Zee's book and looked them a bit. I have also been talking to others that have taken the class in previous semesters. I have a general idea of the failings of nonrelativistic...

Why do people who think that quantum theory is great go on and on that classical particle models are impossible? Why do they never mention fields? There are endless articles in Nature on the latest experiment and why classical particle models won't do. Give or take the de Broglie-Bohm approach...

In plain English, what is the idea behind Group Field Theory by Oriti? How does this involve LQG, SF, and CDT? There is not a popular exposition on the subject nor even a wiki article. thanks

\frac{1}{x-i\epsilon}=\frac{x}{x²+a²}+\frac{ia}{x²+a²}= P \frac{1}{x}+i pi \delta(x) P means the principal value, a is possibly infinitesimal (?), i is the imaginary unit Where does the pi, Dirac delta come from? What principal value? It is from a quantum field theory book.

The question is as follows; 'A free quantum field theory is related to an infinite number of quantum mechanical harmonic oscillators as unit mass particles on springs with spring constants k, where k takes all values. Now imagine the following scenario: these particles also have non-zero...

People say that general relativity and quantum mechanics is not yet combined...i have a doubt,photon is the origin of quantum mechanics and light(photons) is bent by heavy mass and is the origin of general relativity...so this is the relation between quantum mechanics and general relativity..i...

I will be applying for grad school this Winter, but from January 2009-September 2009, I will be done with any course work and will not have any money to commute to my school to continue to do research. So I figured it would be a good opportunity to go further in my mathematics and physics...

I've gone through undergrad courses of QFT, Solid State Physics and Quantum Statistical Physics but the first one didn't cross path with second and third so I only got taste in QFT applications in Solid State Physics through reading Zee's "QFT in a nutshell". My first impressions was WOW! Solid...

I know about string theory, but have heard that string theory is part of the bigger scheme of string field theory, which I think is part of the bigger scheme of M-theory, which is part of the bigger scheme of the Grand Unified Theory. Are my speculations correct, and how long will the Grand...

Hi I was wondering if anyone has a good introductory article about QFT applied to condensed matter physics. I know a bit about condensed matter physics, and a bit of QFT applied to particle physics. thanx

Homework Statement A ping-pong ball of mass 3.0 \times 10^{-15} is hanging from a light thread 1.0 m long, between two vertical parallel plates 10 cm apart, as shown. When the potential difference across the plates is 420 V, the ball comes to equilibrium 1.0 cm to one side of its original...

Hi... I hope somebody can help me... Studying mean field theory in a passage it was necessary to calcolate the inverse of this operator defined on Z^2: $A(I,K)=-J\sum_e \delta(I,K-e)+1/(\beta)*\delta(I,K)$ where I,K pass all ZxZ and the sum on $e$ is a sum on the for basis vectors...

What is meant by BPS state in an interacting field theory? Suppose I have the action for some theory. Now how do I obtain the BPS states for the theory? I am looking for clear steps for calculations. Also I need to know what is special about these states. You may give reference to some review...

i've read that quantum field theory can be applied to condensed matter physics but i don't understand how: quantum field theory is the union of SR with QM but how is SR related to condensed matter physics? i understand that quantum field theory would be useful because it can describe...

I am trying to search for the first person who introduced group theory into quantum field theory.

"FIELDS" by: WARREN SIEGEL C. N. Yang Institute for Theoretical Physics State University of New York at Stony Brook Stony Brook, New York 11794-3840 USA http://insti.physics.sunysb.edu/~siegel/Fields3.pdf

[SOLVED] Quantum Field Theory: Field Operators and Lorentz invariance Hi there, I am currently working my way through a book an QFT (Aitchison/Hey) and am a bit stuck on an important step in the derivation of the Feynman Propagator. My problem is obviously that I am not a hard core expert...

I'm trying to understand why you can get away with using the variational principle on classic fields at all. The variational principle says minimize some value of a function the action. This idea is for point particles and is also motivated by the fact that Newton's laws can be derived via...

[SOLVED] field theory problem Homework Statement If F is a field that has characteristic p, it must contain a copy of Z_p. Is it true that F must sit inside of the algebraic closure of Z_p? My book assumes that it does and I do not understand why? Homework Equations The Attempt at...

[SOLVED] field theory Homework Statement Assume pi is transcendental over Q. Find a subfield F of the reals such that pi is algebraic of degree 3 over F.Homework Equations The Attempt at a Solution Umm...the only subfield I know of the reals is the rationals. Is the answer Q(pi^(1/3))? Do...