Feynman Definition and 617 Threads

My understanding of the n-correlation function is \begin{equation*} \langle \phi(x_1) \phi(x_2) ... \phi(x_n)\rangle = i \Delta_F (x_1-x_2-...-x_n) \end{equation*} Where ##\Delta_F## is known as the Feynman propagator (in Mathematics is better known as Green's function). Let us analyze...

We are discussing the introduction to Einstein field equation, so he start talk about the linearity in Newtonian gravity and the non linearity in GR. But there is somethings I am missing: > " (...) in GR the gravitational field couples to itself (...) A nice way to think about this is provided...

I've been reading a lot of stuff around physics as of late, and I was wondering if the "The Feynman Lectures on Physics: Volumes I, II, III." are a good thing to read? I'm asking as the price for these books aren't cheap, and I want to make sure they are worth the buy.

Renormalization talk by Sean Carroll, "but then I could construct from that the following diagram with four lines in it": In previous talks he explained about diagrams and told interaction can be represented by many (even infinite) number of diagrams, "in" line can be changed to antiparticle...

Hi, there is no other topics in my adventure in Feynman Lectures that makes me so loss in thoughts (https://www.feynmanlectures.caltech.edu/I_44.html). I seem to understand every sentence. But the whole thing is completely unintelligible. Let me start by asking one fundamental question. I am...

Reading the classical Feynman lectures, I encounter the formula(19.53) that gives the radial component of the wave function: $$ F_{n,l}(\rho)=\frac{e^{-\alpha\rho}}{\rho}\sum_{k=l+1}^n a_k \rho^k $$ that, for ##n=l+1## becomes $$ F_{n,l}=\frac{e^{-\rho/n}}{\rho}a_n\rho^n $$ To find ##a_n## I...

Let us first take the S-matrix expansion (i.e. Dyson's formula) \begin{align*} S_{fi}&=\langle f | T \left\{ \exp\left( i\frac{\lambda_3}{3!}\int d^4 x :\phi \phi \phi (x) : + i\frac{\lambda_4}{4!}\int d^4 x :\phi \phi \phi \phi (x) : \right) \right\}| i \rangle \\ &= \langle f | i...

Hi! So I have just been studying Yang-Mills theory advanced quantum field theory. In chapter 72 of Srednicki's book Quantum Field Theory they list the Feynman rules for non-abelian gauge theory. I was asked if I could show some sample allowed diagrams but I could not.. In standard particle...

So there's this professor who insists that the Heisenberg picture is all the rage and much superior in most ways to the Schrodinger picture. He compares it to how you don't use the Hamilton-Jacobi formulation of classical mechanics as much as the Hamiltonian one. Alright, I can buy it. I...

Quantum mechanics is often said to be equivalent with Feynman path ensemble, which "after Wick rotation" becomes Boltzmann path ensemble, also called euclidean path integrals (popular for numerical calculations), or random walk/diffusion MERW (maximal entropy random walk). But Boltzmann path...

Two months late, but I just found out she died back in July. First two paragraphs from the Economist obit which just appeared this week (I'd copy the whole thing but I don't want to do that w/ a copyrighted article) And after she had studied them for a while in adulthood, the statement "no...

Hello! I am a 'mature' learner and am fascinated by all kinds of physics and math ideas. Learning is the key to enjoying science and keeping an open mind. I must admit, I am not very sharp on my physics skills and my calculus is pretty rusty now (I don't work in the science field, per se) so I...

I'm reading "introduction to many body physics" by Piers Coleman. In section 7.2 he's trying to introduce Feynman diagrams by expanding the generating functional. But first he transforms it into this pictorial form: Then he calculates the n=1, m=1 term like below: Which I understand. But I...

Hey there, In QED, we often have Feynman diagrams involving various numbers of non-commuting components, such as for the one-loop vertex correction (Peskin & Schroeder, page 189): The diagram this integral corresponds to is: How do we choose which order to put the propagators and vertex...

Summary:: What is (are) the best book(s) to understand the mathematics of Feynman diagram? Hello, Can anyone recommend some books for the mathematics of Feynman diagram? (I don't mind if they also include the physics; in fact it may be better). Ideally I would need books that are very...

This is probably a simple question but puzzled me a little when trying to explain something to somebody. In all resources online and in most books I've seen, the triple gluon vertex has no overall 'i' factor while e.g. the four gluon vertex always does. The photon and gluon propagators as well...

Consider Moller scattering, that is $$e^-(\vec p_1, \alpha)+e^-(\vec p_2, \beta) \quad\longrightarrow\quad e^-(\vec q_1, \gamma)+e^-(\vec q_2, \delta),$$ where the ##\vec{p}_i,\vec q_i## label the momenta of the in and outgoing electrons and the greek letter the spin state. The two relevant...

Hi, I read the Feynman's book about the quantum electrodynamics and I realized, that he was talking about the different speed of photons. I know, that the light travel's "slower" in a material, but he is also talking about the different speed of photons. I read on the web, that some photons...

I was studying the photon polarization sum process (second edition QFT Mandl & Shaw,https://ia800108.us.archive.org/32/items/FranzMandlGrahamShawQuantumFieldTheoryWiley2010/Franz%20Mandl%2C%20Graham%20Shaw-Quantum%20Field%20Theory-Wiley%20%282010%29.pdf) and got stuck in how to get certain...

I just read the Feynman Lectures about the electron gun experiment with two holes in the middle wall. It demonstrates that if we don't look at the electrons while they travel toward the detector there is an interference pattern in the probability curve of the electrons similarly to what happens...

I have a question on formula (3.1) and (3.2) in Feynman Lectures on Physics III 3-1, available online, https://www.feynmanlectures.caltech.edu/III_03.html <x|s> here can be interpreted also as inner product of bra <x| and ket |s>, following usual Dirac notation ? For example, ##<r_1|r_2>## in...

In the following I will try to deduce the scattering amplitude for a specific interaction. My question is at the bottom, the entire rest is my reasoning to explain how I came to the results I present. My working Let's assume I would like to calculate the second order scattering amplitude in ##...

i want to known whether virtual particle exist or not , and does exchange of particle really happen in interaction.

π+ + π- → γ + γ How do you represent this in a Feynman diagram showing the individual quark? I am very confused please help! [Moderator's note: Moved from a technical forum and thus no template. Own effort below.]

Δ ++ → p + π0 Ξ - → Λ0 + π-

I'm currently working my way through Griffith's Elementary Particles text, and I'm looking to understand what's going on with the underlying Hilbert space of a system described using a Feynman diagram. I'm fairly well acquainted with non relativistic QM, but not much with QFT. In particular, I'd...

Hi, I'm learning how to draw Feynman diagrams in LaTeX using the TikZ-Feynman package, but in https://arxiv.org/ftp/arxiv/papers/1601/1601.05437.pdf I don't see if it's possible to draw loops in ##\lambda \phi^4## theory, how can I draw a loop that goes from one vertex to itself? Thanks

"The “stage” on which the universe goes is the three-dimensional space of geometry, as described by Euclid, and things change in a medium called time." -Feynman Lectures Do the 1st two lines mean that the thing in which everything moves around is the 3 dimensional space...am i interpreting it...

"Suppose we have another ther charge some distance away. Would it feel any attraction? It would feel practically none, because if the first two are equal in size, the attraction for the one and the repulsion for the other balance out.Therefore there is very little force at any appreciable...

I'm not sure that this is an adiabatic process. As far as i can read, it is adiabatic if no HEAT or ENERGY is added. But pumping in molecules that are a non-zero temperature is an addition of energy, no? Anyway - my solution with the assumption of an adiabatic process. (skipping units for...

'Mass is found to increase with velocity, but appreciable increases require velocities near that of light. A true law is: if an object moves with a speed of less than one hundred miles a second the mass is constant to within one part in a million. ' What does 'constant to within one part in a...

Starting from the general formula: $$I_{n,m}=\frac{1}{(4\pi)^2}\frac{\Gamma(m+2-\frac{\epsilon}{2})}{\Gamma(2-\frac{\epsilon}{2})\Gamma(n)}\frac{1}{\Delta^{n-m-2}}(\frac{4\pi M^2}{\Delta})^{\frac{\epsilon}{2}}\Gamma(n-m-2+\frac{\epsilon}{2})$$ I arrived to the following...

So I’m trying to compute the probability amplitude of an electron with momentum p1 and a positron with momentum p2 annihilating into a photons with momenta q1 and q2. My question is how do you use Feynman diagrams to calculate the first and second order expansions (seen in the third image)? I...

Hello, Everyone. I'm happy to announce that the entire collection of (3043) photos taken of Richard Feynman giving his famous 1961-64 introductory physics lectures at Caltech (including his blackboards - original source material for the book, The Feynman Lectures on Physics [FLP]) have been...

Hello everybody! I have to write the Feynman diagrams for the process ##\pi^- + p \rightarrow \Lambda_c^+ + D^-##. It is a strong process since all the quantum numbers are conserved. I have attached my attempt, is it correct? Thank you all in advance!

Summary: Does Richard Feynman's multiple histories ignore alternative histories? Did Richard Feynman's multiple histories (https://en.wikipedia.org/wiki/Multiple_histories) ignore the existence of other alternarive histories or paths? I ask this referring to this comment from this page...

I have been lurking on PhysicsForums for more than a decade. I have been telling myself that I was going to learn physics for fifteen years, but I ended up studying computer science when I returned to school after having been an English teacher for several years. I am currently doing my master's...

In chapter 44 of Feynman Lectures on Physics, Volume I, which covers thermodynamics, we find this passage: Does anyone know what this argument of Carnot's is? I'm not sure exactly what it is that he is supposed to have derived without using the first law. The efficiency of a reversible...

I'm new to QED, so I want to have a general grasp of what's going on. I just want to understand it conceptually. Can anyone explain it in a way so a layman can understand?

Summary: There is some thing i did not get about Multiple History theory Summary: There is some thing i did not get about Multiple History theory I am reading big answers to the big questions from Stephan Hawking. He has mentioned very little about Multiple History theory. I could not...

I'm reading through Lancaster & Blundell's Quantum Field Theory for the Gifted Amateur and have got to Chapter 17 on calculating propagataors. In their equation 17.23 they derive the expression for the free Feynman propagator for a scalar field to be...

Could anyone explain me in simple words what is being said in this topic from this book (great book and author btw)... i don't understand after it starts talking about perpetual motion and lifting and lowering of weights.please explain in simple words. okay someone said to add more details to my...

I started reading QFT recently. With respect to the Dirac spinors, I was introduced to Feynman's slash notation: OR There are sites which say how this can be inserted in LaTeX documents. I checked out the LaTeX guide of PF, but found that it is not listed there. Writing...

I don't entirely get why we usually say that only the shortest path contributes in the path integral. If you calculate the volume of nth fresnel zones which is the locus where the path length is between n-1 and n wavelengths from the shortest path in 3 dimensions, they are the same I believe. So...

611 pages of notes Richard Feynman made in 1961-64 to plan and prepare lectures for Caltech's two-year introductory physics course, later known as The Feynman Lectures on Physics, have been posted in deep-zoomable format at The Feynman Lecture Website. Photos of Feynman giving his...

The term which is relevant for the calculus is: $$ \bar u(p) \gamma^\alpha \frac{1}{\displaystyle{\not}p+\not k} \gamma^\nu \frac{1}{\displaystyle{\not}p'-\not k} \gamma^\beta v(p') \frac{k_\alpha k_\beta}{k^2} $$ $$ \bar u(p) \displaystyle{\not}k \frac{1}{\displaystyle{\not}p+\not k}...

I just finished the intro physics sequence at my college, and I wanted to work through the Feyman lecture Vol.1, with the workbook, over the summer. Does anyone know of any sample curriculum used for this book? Or perhaps, knows a good way to work through the book?

Homework Statement [/B] Hi in the first attachment I am stuck on the sign change argument used to get from line 2 to 3 , see below Homework Equationsabove The Attempt at a Solution [/B] Q1) please correct me if I'm wrong but : ##d^3 p \neq d\vec{p} ## since ##d^3 p = dp_x dp_y dp_z ## and...

I'm trying to go through Mattuck's book "A guide to Feynman diagrams in the many-body problem", the Dover's 2nd edition book. I have read that apparently it has been criticized for being way too easy. I'm having an extremely hard time going through the 3rd chapter, let alone the 4th! I feel...

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...