Feynman Definition and 617 Threads

Just wanted to post a link from Caltech's website hosting the complete Feynman lectures on Physics. All 3 volumes. http://www.feynmanlectures.caltech.edu/

Homework Statement Consider the following real scalar field in two dimensions: S = \int d^2 x ( \frac{1}{2} \partial_\mu \phi \partial^\mu \phi - \frac{1}{2} m^2 \phi^2 - g \phi^3) What are the Feynman rules for calculating < \Omega | T(\phi_1 ... \phi_n ) | \Omega > 2. Homework...

I'm trying to learn how to derive Feynman rules (what else to do during xmas, lol). The book I'm using is QFT 2nd ed by Mandl&Shaw. On p 428 they're trying to show how to derive a Feynman rule for W W^\dagger Z^2 interaction term g^2 \cos^2\theta_W\left[W_\alpha W_\beta^\dagger Z^\alpha Z^\beta...

I'm currently going through the interaction part of Tong's lecture notes on quantum field theory, and I'm a bit confused about how many Feynman diagrams I need to draw in order to compute the amplitude of various interaction terms. Tong presents Feynman diagrams through a series of examples. For...

For internal photon states, is it necessary to sum over the longitudinal polarization state in addition to the transverse states? And if so, does the ordinary Feynman-gauge propagator take care of this? Thanks!

Homework Statement This is more of a general question-- as the title suggests I'm not too sure how to place the terms given by the Feynman rules for fermions (since they involve operators and spinors, the order does of course matter). I've been reading Peskin & Schroeder and the rules are...

I am aware that all three of them are good ones. But, if one is to be picked, which one would it be? I have basic knowledge of mechanics and a little of thermodynamics. I am looking for a book which will further strengthen my basics.

I know there are a lot of similar questions here but just hear me out. I am going to start self-studying quantum mechanics in a few days. I think I am going to use the MIT quantum mechanics 1 lectures as a starting point. But books will be essential as I spend most of my time in school. I have...

Hi, I am trying to figure out how to draw all the three level Feynman diagrams corresponding to this lagrangian density L = \frac{1}{2} \partial _{\mu} \phi \partial^{\mu} \phi - \frac{\mu^2}{2}\phi^2- \frac{\eta}{3!}\phi^3-\frac{\lambda}{4!} \phi^4+i \bar{\psi} \gamma _{\mu} \partial^{\mu}...

Has anyone of you tried to work with creating Feynman Graphs in LaTeX? I tried using the feynmf package, as explained here: https://www.sharelatex.com/learn/Feynman_diagrams and used the same introductory script: \begin{fmffile*}{diagram} \begin{fmfgraph}(40,25) \fmfleft{i1,i2} \fmfright{o1,o2}...

Hello everyone. My name is Sam and I am an engineering student. I am very interested in studying physics. I am currently using physics by Halliday/Resnick/Krane. I have read good reviews on Feynman lectures but not really sure about its content. Is Feynman lectures a good supplement or is it too...

Hi I am trying to write the probability of photon emission due to transition of electron in feynman's path integral formulation. I am stuck trying to figure out the action corresponding to the photon emission. Would anyone shed some light on this? Thanks

Hello, I am learning Feynman diagrams and I still do not understad quite well the symmetry factor idea. The equation is: $$ \frac{1}{O(G)} = \frac{M}{n!(4!)^n} $$ I was trying the next example: If I am not wrong it is O(G) = 10 taking care of the asymmetry of each pair of internal lines...

is there a discussion somewhere on the notion of an advanced or retarded feynman propagator. i don't mean the advanced or retarded propagator juxtaposed against the feynman propagator. I mean the feynman propagator itself with a theta step function multiplied by it to effectively give an...

If I have a scalar field $$\alpha$$ and a Dirac particle $$\beta$$ and its anti particle $$\overline{\beta}$$ such that the three couple to give a vertex factor of $$-ik$$ when evaluating the Feynman diagram (where k is an arbitrary constant). How do I evaluate the first order diagram of...

I am reading Srednicki's book and I am stuck at this point of calculating symmetry factors for Feynman's Graph in the context of dealing with interacting scalar field. First of all my question is what is the standard procedure to calculate it. The way Srednicki has talked about it is that if...

Hello folks, I've just started to read "An Introduction to Quantum Field Theory by Peskin and Schroeder" and at the end of 6th page I could read: "... Since H_I should conserve angular momentum, the photon to which these particles couple must have the correct polarization vector to give it...

Homework Statement The Feynman Propagator is given by <0| T \phi(y)\phi(x) |0> , where T is the time-ordering operator. I understand that this turns out to be the solution to the inhomogeneous klein-gordon equation, etc., but is there any intuitive description of the propagator? Can this...

Good afternoon, I am working my way through the Feynman lectures and I am stumped at Chapter 23, Resonance. Specifically, the derivation of equation 23.12. I have followed up to that point but the appearance of tan (theta) baffles me. The equation is below: Any help would be greatly...

In Introduction to QFT (peskin) 4.5, he writes: The computation for M, of course, will be quite different when identical particles are present. However, I have finished reading the first part of the book and found no special treatment for identical particles. Can anybody tell me how to...

Hi there, I need to draw the Feynman graphs for D→KK meson . I would be appreciate if anyone can help me. Thank you so much.

Homework Statement For the following reactions draw Feynman diagrams, clearly labelling all the quarks, leptons and exchanged particles and stating the type of interaction involved (if more than one interaction could be involved give the most likely): (i) ##\pi^0 \to \gamma + \gamma##...

In the Feynman Lectures on Physics chapter 28, Feynman explains the radiation equation $$\vec{E}=\frac{-q}{4\pi\epsilon_0 c^2}\, \frac{d^2\hat{e}_{r'}}{dt^2}$$ The fact that the transverse component varies as ##\frac{1}{r}## seems fairly obvious to me since what matters is just the angle...

[SIZE="4"]Definition/Summary The Feynman propagator \Delta_F(x) is the propagator (the probability amplitude) for a scalar particle of non-zero mass, m, to travel over a space-time interval x. It is obtained by integrating, over all possible 3-momentums \mathbf{q} of a particle of mass m...

[SIZE="4"]Definition/Summary Feynman diagrams are a combinatorial device for enumerating a sum of integrals of products of delta functions. Feynman diagrams are a mathematical tool with no physical significance. In particular, no single Feynman diagram is intended to represent any physical...

Homework Statement Two gliders are free to move in a horizontal air through. One is stationary and the other one collides perfectly ellastically. They rebound with equal and opposite velocities. What is the radio of their masses? The Attempt at a Solution The answer is 3, how can I...

If one has a 4-fermion vertex, like in Fermi theory : ##G_f (f_1 \Gamma f_2)(l_1 \Gamma l_2)## And you are calculating a one-loop diagram where you have the diagram of : f1-> f2,l1,l2 -> f1 (used for dispersive/unitarity approach) Where in the end you'll use Cutkosky rules to calculate...

https://www.physicsforums.com/showthread.php?t=471333 Is this book with exercise solutions out yet?

I love Feynman's Lectures on Physics and want to go over them again, but I find there's so much of his character is lost when just reading them. I have found a few selected audio versions of his lectures, but I would like to find the COMPLETE set. I know they exist somewhere, as that's how they...

Hi folks, I'm assured that scattering cross-sections in QFT computed at tree level correspond to cross-sections in the classical theory. For example the tree level cross-section for electron-electron scaterring in QED corresponds to scattering of classical point charges. But I'm not sure I...

Hi everyone. I don't know if this is the right place for this thread, but I couldn't find a better one. In one of the Feynman's interviews, he says "So …altogether I can’t believe the special stories that’ve been made up about our relationship to the universe at large because they seem to...

I have made available 5 years of lecture notes presented by Richard Feynman at the Hughes Research labs. The note were hand taken and retranscribed after the 2 hour lectures. The lectures I attended began on the fall of 1966 and represent over 400 hours of lectures. The lectures covered: 1...

Observing which slit a photon or particle goes through in the two slit experiment results in the formation of a diffraction pattern instead of an interference pattern. Were Feynmanns remarks about this made by referring to the classical experiments where there is high illumination or to the...

Hi, I was just trying to draw a Feynman diagram for ψ' to χ_{c} states. So we have a electromagnetic transition. I feel tempted to just have c and \bar{c} coming in and letting a γ leave from one of the legs. But that looks like an incomplete Feynman diagram to me. Maybe I have to get two...

Hi, I've been reading about Feynman diagrams lately and I'm trying to understand the pair annihilation diagram. The picture's here: http://en.wikipedia.org/wiki/File:Feynman_EP_Annihilation.svg I don't understand the following things about the diagram: 1. Why anti-patricles have to...

If we scatter unpolarized electrons off each other and we calculate the amplitude for electrons to scatter into final states and one photon to be emitted do we get destructive interference because the photon can be emitted by either electron? Is one photon emission suppressed in favor of an even...

Hi All, In the Feynman, 'sum over paths' approach to quantum field theory, we compute amplitudes, generating functionals etc by feeding in a "classical action". By calling the Lagrangian that we feed in "classical", this mean that the fields that feature in that action are regarded as...

For a 2nd order electron-positron scattering, the following diagrams are possible: http://www.quantumdiaries.org/wp-content/uploads/2010/02/eepp-1024x228.png My question is: What is the meaning of the right diagram - is a photon created and annihilated instantaneously? how is this possible?

the number stand for the index of particles (quarks and gluons) M=\bar{v}(p_2) ig_sT_{12}\gamma^\mu(12)u(p_1)\frac{-i}{p_7^2}\bar{u}(p_5) ig_sT_{56}\gamma_\mu(56)\bar{v}(p_6)\frac{-i}{m-\gamma^\mu p_{9\mu}}\bar{v}(p_3)...

I need help :( How can I draw a Feynman Diagram, starting with a Lagrangian?

I read the book of "quantum field theory in nutshell" by A. Zee. There is a "baby problem" in Page 44. I can't understand how to get the diagrams of Figure 1.7.1 from the calculation of -(\lambda/4!)(d/dJ)^4 differentiating [1/4!(2m^2)^4]J^8. How to associate this term to the three diagrams...

I met a problem when I read the textbook "Relativistic Quantum Mechanics" by J.D.Bjorken. He said we can get the potential V(r_1,r_2)=\frac{f^{2}}{\mu^{2}}(1-P_{ex})(\tau_1\cdot\tau_2)(\sigma_1\cdot\nabla_1)(\sigma_2\cdot\nabla_1)\frac{e^{-\mu|r_1-r_{2}|}}{|r_1-r_{2}|} (10.51) from the...

I understand that Feynman diagrams can be expressed either in the position or momentum representation. Is the 4-momentum conserved at the vertices in each case or only in the momentum representation?

Hi, I am drawing Feynman diagrams for various Higgs decay channels. There are two diagrams I am stuck on and there aren't many examples online. They are H→gg and H→Z\gamma For the H→gg decay I had a stab at drawing the reverse of the gluon fusion diagram. Higgs decaying to two gluons via a...

Homework Statement Hey guys, so I'm new to Feynman diagrams, and I have a few to draw but i'll start with the first one. I'm being asked to draw the following process: \pi^{0}(uu* or bb*)→\gamma +\gamma. I have to "clearly label each quark, lepton and boson, and say which fundamental force...

I have been reading the explanation of reflection that Feynman provides in The strange theory of light and matter. There are two things I do not understand: a) How does he choose the directions of the little arrows below the diagram? I understand that each path is different in that it...

In his layman's guide to QED Feynman defines a particle propagator as a function that gives you the amplitude that a particle, that was initially at spacetime event ##x##, will be found at spacetime event ##y##. But does this definition assume that the particle is unique so that if you find...

Consider the Feynman diagram below from, http://hyperphysics.phy-astr.gsu.edu/hbase/particles/expar.html where I assume time runs upwards and the gluon in the graphic runs horizontal and is labled as a green_antiblue gluon. If the gluon runs horizontal can one still label a gluon as being...

Was reading my old copy of Surely You're Joking Mr. Feynman again; ran into the anecdote about the Feynman sprinkler. In the book, one guy argues that the water going into the sprinkler will cause the same centripetal force as the water going out of the sprinkler, causing a torque in the same...

The theorem states \frac{\partial E}{\partial \lambda} = \langle \psi \mid \frac{\partial H}{\partial \lambda} \mid \psi \rangle Where \mid \psi \rangle is an eigenket of H. An example (given on Wikipedia) is to find \langle \psi \mid \frac{1}{r^2} \mid \psi \rangle for a Hydrogen...