Feynman Definition and 649 Threads

Hi guys, And Happy new year :) I am revising for a module on relativistic quantum mechanics currently that I took some time ago. A large portion of the module, and hence the exam involves drawing Feynman diagrams and computing invariant amplitudes. The part I am a little rusty...

Is there an on-line list of all possible Feynman diagrams for all the known particles?

I recently started reading Feynmans book QED. There are a couple of questions I have regarding his theory on the percentage of light that is reflected of two surfaces of glass. My question is as follows, A piece of glass in fact has four surfaces. The front of the glass the back side of...

Attempting to understand the following: Compton scattering can happen either (a) an electron could absorb a photon and later emit a photon, or (b) an electron could emit a photon and later absorb a photon. OK, the maths works out, but I am trying to get intuition on track. These two are...

1. The problem statement In calculating the amplitude for the diagram[1], view 1.jpg. [1] Voja Radovanovic, Problem Book Quantum Field Theory 2. Homework Equations View 2.jpg. The Attempt at a Solution View 3.jpg.[/B] Why the integrals is divergent? Why the other terms are finite?

I was studying Feynman Lectures on Physics Volume 1 chapter 29. In there he proves that electric field propagates like a wave. Here is my attempt (in image), please tell me my mistake. Thank you

This is one of the problems I'm currently working on but understanding how to deduce the Feynman rules for this case would give me a better idea on how to do it for more general cases besides ##\phi^4## theory (which is the example commonly covered in books like Peskin and Greiner). 1. Homework...

I am looking for good references / clarifications on the subject. First of all, my question is concerned only with mathematical formulation of something that sort of plays the role of the Feynman path integral of the "standard" QFT. It is not concerned with the physical or philosophical...

Hello, I assigned a work packet to my IB Physics students that guides them through how to make Feynman diagrams. This particular problem seems to have some issue, but perhaps it is something that myself and my class have all over looked. Note: At the beginning of the packet it states that some...

I’m currently self-studying from Feynman & Hibbs Quantum Mechanics and Path Integrals, but having trouble with a statement in the chapter on time-dependent perturbations. Background: They define $$V_{mn}(t_c) = \int_{-\infty}^\infty \phi_m^*(x_c)V(x_c,t_c)\phi_n(x_c)\,dx_c,$$ where V(x,t) is...

The logic of the Feynman Propagator is confusing to me. Written in integral form as it is below $$\Delta _ { F } ( x - y ) = \int \frac { d ^ { 4 } p } { ( 2 \pi ) ^ { 4 } } \frac { i } { p ^ { 2 } - m ^ { 2 } } e ^ { - i p \cdot ( x - y ) },$$ there are poles on the real axis. I have seen...

First, is it suitable to solve a Green's function by one-order self-energy, since it only consider partial high order perturbation, so it's unclear that this calculation corresponding to which order perturbation. In other word, if one wants to use self-energy to get Green's function, he should...

I'm trying to work out the Feynman diagrams for scalar-scalar scattering using the Yukawa interaction, as given in Chapter 6 of Lahiri & Pal's A First Book of Quantum Field Theory. The interaction hamiltonian is $$\mathscr{H}_{I}=h:\overline{\psi}\psi\phi:$$ where ##\psi## is a fermion field and...

In Peskin's textbook section 7.3 The Optical Theorem for Feynman Diagrams(Page233), he said it is easy to check that the corresponding t- and u-channel diagrams have no branch cut singularities for s above threshold. But I can't figure out how to prove it. Can angone help me? Thanks!

Homework Statement Homework Equations The Attempt at a Solution The moment of inertia before collapse is for each rod: BEFORE COLLAPSE:[/B] Ib = ∫(L2 + x2) dm = m/L ∫(L2 + x2) dx = 4/3 * m * L2 We have 8 of these plus the inertia of the mechanism, giving a total I, It = 8 * Ib + Ik =...

Hello, I have a question. In Feynman lectures vol. I, in chapter 37-2, Feynman has an experiment with bullets. *Copyright http://www.feynmanlectures.caltech.edu/III_01.html But the curve for ##P_{12}## looks in the picture is different from his live recorded lectures. *YouTube - Is the...

http://nautil.us/issue/59/connections/another-side-of-feynman?utm_source=Nautilus&utm_campaign=96110cf12d-EMAIL_CAMPAIGN_2018_04_25&utm_medium=email&utm_term=0_dc96ec7a9d-96110cf12d-50637757 is a Nautilus article containing excepts of letters Freeman Dyson wrote that are concerned with Richard...

Homework Statement Vertex Feynamnn rule for computing the time correlator of fields under an action such as, for example, Say ##S_{int} [\phi] =\int d^4 x \lambda \frac{\phi^4(x)}{4!} + g \frac{\phi^4(x)}{4!} ##, ##\lambda## and ##g## the coupling constants. Homework Equations see below...

I learn quantum field theory using the book of " quantum field theory in a nutshell" by A. Zee. But I am confuse when I read the content about the "baby problem" at the beginning of "1.7 Feynman Diagrams". In that section, author get the term of order λ and [J][/4] by -(λ/4!)[(d/dJ)][/4]...

I am reading Peskin and Schroeder and finished a few years ago Srednicki. What I don't understand is why do Feynman rules work? They are supposed to represent the diverging integrals that appear in the calculations, i.e momentum integrals, are they supposed to be regarded as a pictorial...

In paragraph 5.7 of this lecture, Feynman explains how to calculate the apparent area of the nucleus, in a sheet of unspecified material. I have two questions about the formula used by Feynman. 1) Although the sheet has a thickness, the formula considers only the superficial area of the sheet...

The lecture is here, paragraph 5-7. Feynman is trying to explain how to measure the size of the nucleus. He writes : "Suppose we have a piece of material 1 centimeter thick. There will be about 10^8 atomic layers. Since we don't know the size of the nucleous, how can be possible to calculate...

Homework Statement Consider four real massive scalar fields, \phi_1,\phi_2,\phi_3, and \phi_4, with masses M_1,M_2,M_3,M_4. Let these fields be coupled by the interaction lagrangian \mathcal{L}_{int}=\frac{-M_3}{2}\phi_1\phi_{3}^{2}-\frac{M_4}{2}\phi_2\phi_{4}^{2}. Find the scattering amplitude...

Hi, last year I've decided to re-study physics starting from the very basis in my spare time. It is taking some time but it has been pretty fun and useful. I'm an engineering undergrad and the most advanced physics class I had was an introduction to QM, but right know I'm more focused on...

In the first diagram above, if I understand it correctly, the photon turns into an electron positron pair and then back again to a photon. However, what exactly is happening in the second diagram at the bottom left hand corner? Is the electron being converted to an electron photon pair?

Griffith's Introduction to Elementary Particles, if I understand it correctly, states that in QED, the fine structure constant contributes less and less to the strength of the EM interaction as we add more and more vertices since the constant is so small (1/137). However, in QCD, since the...

In the following Møller scattering process, two electrons enter, exchange a photon and then leave (and if I understand this correctly, we say that both of the electrons emitted a photon). However, in this case: We have an electron scattering off a photon, but the interaction happens by an...

In the first Feynman diagram, an electron comes in, emits a photon and then leaves. Is this an allowed process? Because if you rotate the diagram by 90o, the diagram should be just as valid, but it doesn't seem to be since it would violate the law of conservation of momentum. So is the...

While doing research on Feynman and Bohr, I came across how Bohr never warmed up to Feynman even though he frequently sought him out for discussions in Los Alamos - which lead me to this question. Reasons were given for why he may not have, but that still leaves me wondering if there was...

I have been learning SR from various sources. Most of the time from Feyman's Lectures but that's not the only place. In II_26 he gives the transformation for the E-field of a moving charge in the x direction under a standard Lorentz configuration. In Eqn 26.11 he derives a formula for the Ex...

Hi all, would appreciate a spot of help on this problem which originally comes from Feynman's introductory physics course. 1. Homework Statement 'A spar buoy of uniform cross-section floats in a vertical position with a length L submerged when there are no waves on the ocean. What is the...

I am currently going through a friend's Mechanics II notes and homework before I take the course at a different university next semester. I have a few problems that I am having trouble understanding and am posting here for help. 1. Homework Statement 1. A solenoid is on, Flux is Φ. 2. The...

Greetings, I have begun reading the Feynman Lectures to repeat the most important ideas from my undergraduate studies and to improve my intuitive understanding of physics. In one of the first chapters, the one about the conservation of energy, he demonstrates that the conservation of energy is...

I'm reviewing relativity and am working simple problems to test my understanding. I am reviewing Feynman's HTML book on physics. I don't get the same answer as him for the shape of an E field in a moving particle in one dimension, equation 26.11, but I do get his answer for equation 26.10; and...

I am pretty sure that I would be comparing apples and oranges in this question, but as I usually learn something from the responses telling me in detail that my question is silly, here goes: Does the phase used as a weight in Feynman's path integral formulation (i.e., the quantum action S in...

How exactly does the mere act of observing collapse the wave function of, say, photons? I don't quite understand that one. And Richard Feynman's question related to Young's double slit experiment and the fact the electron went through both slits, as well as neither, and just one slit, and just...

Hi, I've just started studying Feynman's thesis and am in need of some discussion regarding the three principles he put forward on the development of his 'Principle of least action in quantum mechanics'. The three principles are 1) The acceleration of a point charge is due to the sum of its...

Could somebody explain me this?: Why is the arrow of the electron-antineutrino pointed towards the W-boson and not as in the second picture upwards? This is my first post and also haven't learned too much about physics yet so please if anything is unclear hit me up.

1. The declaration of the problem, all variables and data given / known Calculate the decay amplitude of ## \pi ^ 0 ## in an electron-positron pair ## \pi^0 \rightarrow e^+ e^- ##, assuming that the interaction is of the form ## \mathcal {L}_{int} = g \: \partial_{\mu} \phi \: \overline{\psi}...

In his popularized version of QED (Strange Theory...) Feynman explains reflection from an air-water boundary (including total internal reflection) by summing up the amplitudes of various paths that bend at the boundary but are straight everywhere else. As we add more contributions, we see a...

Homework Statement Homework Equations Conservation of momentum: m1*v1 + m2*v2 = k Conservation of mech. energy 1/2 * m * v^2 + m * g * h = k The Attempt at a Solution Why can't i just use conservation of energy to solve this one? I know that the bullet contains all the kinetic energy before...

Homework Statement Homework Equations F = ma The Attempt at a Solution The gravity pulls on m with a force Fg: Fg = m*g This force is directly translated into pulling the total mass m+M with an acceleration a: (m+M)*a = Fg <=> a = Fg / (m+M) = m*g / (m+M) with this acceleration, we can...

As always a fairly devious problem from Feynman, it's getting the better of me and I imagine some of you may be able to solve! Excuse the poor drawing. He writes 'Consider cylinders radius πcm, he cylinders are chopped into thirds and two thirds are connected as shown in fig. The thirds have...

Hi everybody. I enjoy looking at other people's handwritten notebooks, as well as what textbooks they learned math and physics from. This evening I came across this article about how Feynman learned calculus in high school by studying Calculus for the Practical Man by Thompson. He kept very...

Hello, I recently watched a video as an introduction to Feynman diagrams for my own self-interest. The video gave a link to practice problems, and one of them was as follows: In a neutron star gravitational collapse causes valence electrons to combine with protons. Draw a Feynman diagram...

I'm reading "Teaching Feynman’s sum-over-paths quantum theory" by Taylor et al. http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.374.4480&rep=rep1&type=pdf, I'd like to confirm whether my understanding is correct, so a couple of questions. 1. We need to try and think of all kinds of...

Hi guys, So I'm trying to compute this Feynman integral: $$ V=\dfrac {-i} {2} \int {\dfrac {d^4 k} {(2\pi)^4}} \dfrac {1} {k^2 - m^2} \dfrac {1} {(k+P_1)^2 -m^2} \dfrac {1} {(k+P_1 +P_2)^2 -m^2}$$ I have introduced the Feynman parameters and now have the integral: $$ V=-i \int...

I am going through Shankar's treatment of Feynman Integrals right now, and I have one lingering doubt that I can't quite seem to work out. I was pretty happy with the idea of discretizing time, then doing independent sums over xi at each time. But Shankar simply says that we can consider the...

Homework Statement "A mortar emplacement is set 27,000 ft horizontally from edge of a cliff that drops 350 ft down from level of mortar...It is desired to shell objects concealed on the ground behind the cliff. What is the smallest horizontal distance d from the cliff face that shells can reach...

Hi, I'm trying to compute the cross section of a gluon emission from quarks in a electron-positron annihilation at first order (I attach the diagrams below). Applying the Feynman rules the matrix element should be: My problem is that I have no idea where this minus sign comes from. (I obtain...