Feynman Definition and 649 Threads

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...

Let us assume that we want to describe the full process of photon emission by electron A and absorption by electron B. Therefore electron B must be on the forward lightcone of electron A. In the normal forwards in time description a virtual photon propagates from A to B depositing a certain...

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...

How can we demonstrate that the symmetries of S-Matrix can be applyed to parts of Feynman diagrams?The S-Matrix is the sum of infinite diagrams,why we know each or part of each diagram has the same symmetries as the symmetries of S-Matrix?

I read the Quantum Physics section of the online version of Feynman lectures http://feynmanlectures.caltech.edu/I_02.html#Ch2-S3 and I don't understand how he can deduce electron momentum from the Uncertainty Principle. I agree that the momentum is uncertain but how can he deduce that it is very...

I read the Quantum Physics section of the online version of Feynman lectures http://feynmanlectures.caltech.edu/I_02.html#Ch2-S3 and I don't understand the problem with the electrons "breaking away from the nucleus". So why can't the electrons just keep going in and out of the nucleus ?

Greetings, I think this will be a very quick thread. I am new to using Feynman diagrams, and have run into something that I find puzzling. The lowest-order Coulomb interaction Feynman diagram is (image from Wikipedia Moller Scattering article)...

Homework Statement I need to calculate <\phi(x_1)\phi(x_2)\phi(x_3)> and <\phi(x_1)\phi(x_2)\phi(x_3)>_{c} and then draw Feynman diagrams when \mathscr{L} = -\left(\left(\partial_{\mu}\phi\right)^{2} + m^{2}\phi^{2}\right) - g\phi^{3} through first order in g. Homework Equations...

Have you ever wished there was a high-quality up-to-date version of The Feynman Lectures on Physics available online? One that could be read with a browser so you could study FLP on your smartphone, tablet, notebook or desktop computer, whenever you felt like it? For free? Well, now there is...

Is there a list of matrix elements for elementary processes? ##f\bar{f}\to\gamma\to f^\prime\bar{f}^\prime## ##f\bar{f}\to Z^0\to f^\prime\bar{f}^\prime## ##ff^\prime\to W \to \ldots## ##qq^\prime\to \ldots## ##\ldots##

I have found an error in the QFT book by Mandl & Shaw, 2nd ed. In eqn (8.53), there is a minus sign in front of e^4. However, this cannot be justified on the basis of how the equation is derived. In the unnumbered eqn below eqn (8.52) there is a minus sign, and the trace in this eqn is to be...

I just Read arithemetic for the practical man and found really interesting...there's also Algebra for the Practical Man,Geometry for the Practical Man,Trigonometry for the Practical Man,Calculus for the Practical Man And everybody knows that the great feynman learned from these books...I would...

Apparently Bill Gates bought some tapes and released them to the public. I've been listening to them all day, and I'm enjoying the hell out of them. In lecture #2, the one on the relationship between mathematics and physics, he talks about how mathematics is the language of physics but that...

"Feynman" of Chemistry? Does anyone know if a chemistry book exists akin to Feynman's fundamental physics books?

I am studying QFT from Srednicki's book. Let me ask a question about symmetry factor from this book. Let, for specific values of V and P from eqn (9.11) we get some terms. One of them is a disconnected diagram consisted of two connected diagrams C_1 and C_2. The disconnected diagrams...

I am learning QFT from Srednicki's book. However, in Figure 9.2 Srednicki has given all connected diagrams with E=0 and V=4. Are there any way to know the disconnected diagrams? Can you tell me what they are.

Homework Statement I have this 2^n*2^n matrix that represent the evolution of a system of $n$ spin. I know that I can have only one excited spin in my configuration a time. (eg: 0110 nor 0101 ar not permitted, but 0100 it is) s_+ is defined with s_x+is_y and s_- is defined with s_x-is_y...

I have a request for some explanation in Feynman diagram concerning repelling/attraction of electrical charges. I have been told that when two charges (say, e1(-) and the e2(-)) repel each other, a photon is being emitted from one of them, and the other charge is later being hit by this photon...

Feynman Parameters--Peskin&Schroeder 6.44 I'm having some trouble deriving equation 6.44 on p.191 of Peskin and Schroeder (my book is the fifth printing, December 1997). The algebra comes close but I think that you need to do some arguing to actually get his answer--maybe this requires some...

In reading Ryder's book on quantum field theory he advocates reading off the Feynman rules directly from the Lagrangian in the path integral quantization method. I can sort of do this in phi-four theory, but it is not obvious in for example Yang-Mills theory, so I wondered if someone could...

Hi all Just a basic question really; I'm at university and have been tutoring someone through a couple of A level physics modules, and I'm covering some basic particle physics at the moment, which is all alright, but I've come to an issue with Feynman diagrams. Basically, for interactions...

Does anyone have a link or a reference to somewhere where these rules are explicitly derived for phi-four theory?

I'm trying to follow Feynman's explanation on page 26-10 of Volume 2 of The Feynman Lectures on Physics. He describes the electric and magnetic fields in a FoR S' moving between the plates of a condenser. Feynman writes that we see a reduced E and an added transverse B in S'. I've attached a...

Hi everyone. I have a very silly question. What is the Feynman rule for external legs of spin-zero boson? Is it just to multply by 1? Thank you

Hi guys! A serious doubt just passed through my mind. It is probably a silly question. In writing the Feynman rules for QCD, we know that the quark-gluon vertex is given by: $$-ig\gamma_\mu T^a_{ij}$$ where T is the SU(3) generator and i and j are the colors of the incoming and outgoing...

So apparently a neutral pion is a superposition of u\bar{u} and d\bar{d}. I'm having trouble understanding what this means. I have no problem understanding how the decay products of some scattering experiment could be a superposition of these two states, but how can we treat this superposition...

I've been doing some review of particle physics in Griffiths and I came across this statement that really didn't stand out to me before. "the idea is to draw all the diagrams contributing to the process in question (up to a desired order), calculate the amplitude (M) for each one, and add...

I've been given an action of S = -\frac{1}{2}m^2\phi^2 - \frac{\lambda}{3!}\phi^3 and the question then require drawing the feynman diagrams for the <\phi\phi> at order \lambda^2. I am told that there are 2 connected diagrams at one-loop order and one disconnected two-loop diagram and...

Hi all. I am new here but i decided to work a bit more and finish my diploma faster so i think i will use this forum more from now on. I was studing about quark color changes, quark interactions, gluons and generally the strong force. As i saw the Feynman diagrams i felt a bit confused...

I don't understand how the last equation in the attached picture is derived from equations 9.40 and 9.39, can anyone help?

Homework Statement Is the following reaction possible? If so, by what force? Draw (one of, if applicable)the lowest order Feynman diagrams for the process. n + n-bar --> ∏+ + ∏- + ∏0Homework Equations N/AThe Attempt at a Solution This process, it seems to me, should be possible. It...

Author: Richard P. Feynman, Robert B. Leighton and Matthew Sands Title: The Feynman Lectures on Physics Amazon Link: https://www.amazon.com/dp/0201021153/?tag=pfamazon01-20 http://www.feynmanlectures.caltech.edu/ (free) Prerequisities: Contents:

As per the Wheeler Feynman absorber theory, there cannot be electromagnetic radiation without an emitter and absorber. If we had only a single electron in the universe then disturbing it (accelerating it) would not produce any radiation since there was nothing to absorb it. Hence it would...

Hi Guys. I'm hoping that you might be able to help me out with a question I have about anti-particles in Feynman diagrams. I'm drawing these again for the first time in over a decade because I'm teaching an elementary physics course that requires the students to draw diagrams for a few...

I know this is an odd topic. The Feynman Lectures seem to be universally acknowledged as a great way to learn and grasp some of the simplest and most difficult concepts in physics. I am almost done the first volume and I really am enjoying the lectures. The odd thing is, I can't put my finger on...

Hi all, Having learned much about technicalities in Grand Unified Theory, I have known that it's basically pursuing the belief that coupling constants of all interactions converge to the same value. My question is, do Feynman rules still hold in this theory (b/c each type of interaction...

Would it just be the same as with two electrons? (or any other pair of particles with the same charge) I'm kinda in two minds, I suspect that is wrong because wouldn't the fact that they attract each other (instead of repelling) means that the diagram would be drawn differently?

Feynman diagrams from "Quarks and Leptons" Halzen and Martin? The following scan is from Quarks and Leptons: An Introductory Course in Modern Particle Physics, Francis Halzen (Author), Alan D. Martin (Author), page 9. Can I take anything from the topological difference between figure (b) and...