Feynman Definition and 617 Threads

Given a diagram, how is one supposed to apply the feynman rules to calculate the feynman amplitude?

For quartic scalar field theory these are some of the lowest order diagrams (taken from the solutions to 9.2 srednicki). I'm wondering if someone can give me an intuition of how to actually calculate them. What I'm thinking is that vertices are $$\int \frac{d^{4}x}{(2\pi)^{4}}$$ and for the...

On page 60 of srednicki (72 for online version) for the $$\phi^{3}$$ interaction for scalar fields he defines $$Z_{1}(J) \propto exp\left[\frac{i}{6}Z_{g}g\int d^{4}x(\frac{1}{i}\frac{\delta}{\delta J})^{3}\right]Z_0(J)$$ Where does this come from? I.e for the quartic interaction does this...

Hi!, I am studying for an introductory course in QED and Feynman Diagrams. Everything we see is like a first order approach and I am having some trouble understanding antiparticles in Feynman Diagrams: Why is it that we put an antiparticle that is leaving as if it is entering the interaction...

I'm trying to draw Feynman diagrams with the feynarts.sty package for LaTex. The problem is that if I write the following code \begin{feynartspicture}(150,150)(1,1) \FADiagram{} \FAProp(0.,10.)(6.,10.)(0.,){/Straight}{0} \FALabel(3.,9.18)[t]{$1$}...

Please check my logic. 1. Feynman diagram is a tool to calculate 'final state' from an 'original state'. It is mostly used for simple processes, like scattering. 2. 'Final state' usually have a precise meaning due to observation of particles trajectories. 3. However, in MWI there is nothing...

Homework Statement Compute the matrix element for the scattering process \phi \phi \to \phi \phi Homework Equations The Lagrangian is given by L = \frac{1}{2} \partial_{\mu} \phi \partial^{\mu} \phi + \frac{\alpha}{2} \phi \partial_{\mu} \phi \partial^{\mu} \phi + \frac{\beta}{2} \phi^2...

Homework Statement The lagrangian is given by: L = \frac{1}{2} \partial_{\mu} \phi \partial^{\mu} \phi + \frac{\alpha}{2} \phi \partial_{\mu} \phi \partial^{\mu} \phi And the question is to find the feynman rules. Homework EquationsThe Attempt at a Solution I started by using the...

I want to compute the following when the 4-vectors are already given i.e x^{\mu},y^{\mu} are given and are orthonormal ( x, y are complex vectors); \begin{eqnarray} \left(/\negmedspace\negmedspace x/\negmedspace\negmedspace y\right)^{2} & = & /\negmedspace\negmedspace...

I'm in the 11th grade and have little education of college level mathematics. I individually find myself studying one section of it but hardly have a grasp. I really want to read the Feynman Lectures to further my education of physics, but as I read over the pdf it looks like there is a lot of...

After reading some of the other posts on the Forum, I'm clear on the fact that Bohmian trajectories (of the de Broglie Bohm formulation) and the paths of the Feynman path integral formulation are very different things. I'm wondering (and it's a naive question, no doubt), when talking about...

Consider the lowest order interaction e.g. e- e+ -> virtual photon-> muon anti muon. I appreciate that the electron-positron pair cannot annihilate into a real photon due to conservation of 4-momentum, but why is the pair permitted to produce a virtual photon? I know that virtual particles...

Hallo Everybody, I am searching for a book (or lecture notes) that details the calculations that lead me from a given Lagrangian to the Feynman rules of the theory. It should not be rigouros, just the main steps to get the Feynman rules. Thanks for your help!

Firstly, let me talk about my BC exam situation first and then the Physics C exam secondly. I just recently downloaded a PDF full of released BC exams from 1969 to 1998. Is there any PDF for a fully released BC exam from last year(2015)? What is the best textbook that is oriented towards this...

Consider a ##j## point all massive leg one loop polygonal Feynman diagram ##P## representing some scattering process cut on a particular mass channel ##s_i##. Invoking the relevant Feynman rules and proceeding with the integration via dimensional regularisation for example gives me an expression...

I have been going through feynmans lectures on probability and have a few questions that i can't answer ; in the part regarding fluctuations he introduces us to tree diagrams(pascals triangle ) and gives an example regarding the toss of a coin If we consider the no. Of tosses as n and no. Of...

¿How is possible deduce the Lagrangian of the fields of a theory knowing only his Feynman Diagrams?

I am reading the book tilted "quantum field theory in a nutshell(second version)" by A.Zee. On the page 45, for example there is a term \frac{1}{m^2}λJ^4. The question is that how to related it to the Figure 1.7.1. or that, How can I draw the three diagrams in Figure 1.7.1 from the term...

Hi everyone, sorry if this is not the right place to post that question but I'm new to this forum, i'll delete if necessary. I am currently trying to learn QFT from Matthew Schwartz's "Quantum field theory and the standard model", quite clear during the first chapters, but i have been...

I am not sure if this is the right part of the forums to post this, but I was reading the book Surely you're joking Mr Feynman when i reached this part: This got me thinking. How does one "understand" physics and mathematics? It's certainly more than remembering some formulas. What do you think?

Hi, i have some trouble with feynman rules after wick's rotation. I don't understand how the propagators transform. In particular if i take the photon's propagator in minkowskian coordinates i don't understand where the factor "-i" goes after the transformation. ## \frac{-i\eta_{\mu\nu}}{p^2}...

For some reason, I'm having trouble with what I feel should be a relatively simple derivative to take. Feynman is differentiating the potential to find the z-component of the electric field. He has: -\frac{\partial \phi}{\partial z} = - \frac{p}{4 \pi \epsilon_0} \frac{\partial }{\partial z}...

Hi there, In paper as : http://authors.library.caltech.edu/8947/1/GREprd07.pdf I don't understand the colour factor associated with two gluons and single octet scalar as the first Feynman diagram in fig. 3 ? In eq. 27, this colour factor is given by ## (d^{abc})^2 ## .. so, how did this come...

I've been learning about Greens functions. I'm familiar with how to find them for different differential operators and situations but far from fully understanding them. We were shown in lecture how they can be used to obtain a perturbation series, leading to Feynman diagrams which represent...

Nonlinear sigma models are particular field theories in which the fields take values in some nontrivial manifold. In the simplest cases this is equivalent to saying that the fields appearing in the lagrangian are subject to a number of constraints. Since the lagrangian fields are not independent...

Hi. Do you know any book/paper/lecture notes where I can find complete derivation of Feynman rules for both scalar and pseudo-scalar Yukawa theory, and maybe an example of application to decay of fermion?

Homework Statement :[/B] For the decay of the ∆+ → n + π+, sketch an appropriate quark-level Feynman diagram. State which interaction is responsible for this decay. 3. The Attempt at a Solution This is more of a question to see if I'm doing it right more than anything. The first Feynman...

Greg Bernhardt submitted a new PF Insights post Think You Know Richard Feynman? Continue reading the Original PF Insights Post.

Im working on deriving the final expression on the attached picture. The problem is that of a particle in a potential coupled to a "bath" of harmonic oscillators but I'm not sure how you arrive at the final expression. First of all, why are you allowed to assume that q is periodic on the...

Hello, I am reading the volume 2 of the Feynman's Lectures on Physics, and something is bothering me when he calculates the dipole moment of a single atom induced by an extern field ...

Hello, I am reading the volume 2 of the Feynman's Lectures on Physics, and something is bothering me when he calculates the dipole moment of a single atom induced by an extern field ...

I'm hoping that someone can help me understand a topic on page 86 of Feynman's "Six Not-so-easy-pieces", in the "4-4 Relativistic mass" section. He says, "It is an interesting exercise to now check whether or not Eq.(4.9) is indeed true for arbitrary values of w, assuming that Eq.(4.10) is the...

Looking to buy a copy of the Feynman lectures and the millenium edition is the one I am going to buy. I remember reading, maybe I am mistaken, that there was reprint of the 2011 millenium edition. If I am correct, this reprint fixed errors that were found in the 2011 editipn. However, when I...

Hi there. I'm reading Jackson's Classical Electrodynamics. 1. Homework Statement In chapter 6, the equation for the electric field of a moving point charge is derived. I could follow the mathematics to get the electric field for the moving charge, which is given in equation 6.57 in Jackson...

Supposed to represent a relativistic proton colliding with a stationary proton, leading to changes in the momentum of both and the production of a neutral pion. The pion then decays into two photons. No clue if this is right. I've never drawn anything much more complicated than...

First I would like to say that I'm sorry if this question has been asked before- I'm new here. I was reading QED by Richard Feynman, and he mentioned that any given antiparticle is just it's regular particle counterpart moving backwards in time. How is this possible? I thought that it was only...

The arrows in a Feynman diagram represent electric current. right? If this is the case then why do neutrons and neutrinos have arrows. How do they have an electric current?

In this process: N*→N+photon If we want to calculate the amplitude with the following interaction Lagrangian: (http://arxiv.org/abs/nucl-th/0205052) If we use functional method,the field operator is not polynomial,how to use "center formula"to bring functional derivative in? Or we must...

Exchange Particles are to show the transfer of (for example) +/- charge to the other side so the charges balance. But I don't understand... Beta plus decay: p → n + e+ + νe. This is just an example, the Feynman diagram shows a W+ boson transferring the positive charge to the right hand side...

Hi all, I was thinking about the problem and can someone verify my solution : 1) Set up a Magnetic field going from down to up, i.e north pole is at the bottom. 2) Use the triboelectric series to charge some small particle positive (hair or glass with teflon) 3) Throw that particle in forward...

I thought the fundamental electromagnetic vertex is Why is the following diagram below allowed? The 'special' feynman diagram for compton scattering ##e^- + \gamma \rightarrow e^- + \gamma## is

Homework Statement I am making an old exam of a particle physics course, and i know how to calculate the cross section for example for bhabha or moller scattering. now one of the questions on the old exam is: Explain why e-+ e+ -> γ is zero, but i am not sure why this is, can someone explain...

Feynman Path Integrals are a way of calculating the wave function of quantum mechanics. It usually integrates every possible path through all of space. I wonder if there is any study of Feynman path integrals through a space with holes in it - with regions of space excluded from the integration...

Dear community! I watched The Big Bang Theory and watched this episode. If you click on it you would get to a homepage - if you scroll down you would get to a section called Episode Questions -> Physics Bowl. According to the newspapers The Big Bang Theory have an employee who is scientist...

I think I can safely say that nobody understands quantum mechanics. ~ Richard Feynman

Homework Statement (a) e- + e+ -> e- + e+ (b) e- + e- -> e- + e- c) e- + e- -> e- + e- + u+ + u- d) y -> e+ + e- e) y + y -> y + y Homework EquationsThe Attempt at a Solution Part (a)[/B] Part (b) Part (c) Part (d) Part (e) Not sure what to do with this, since usually the...

Page 260: "No modification of quantum electrodynamics at high frequencies is known which simultaneously makes all result finite, maintains relativistic invariance, and keeps the sum of probabilities over all alternatives equal to unity." Is that still true today?

Hey guys, I need help with conserving momentum at these vertices (this is Bhabha scattering): So in Diagram (a), the first vertext to the left. The incoming momenta are p_{1}+p_{2}. The outgoing momentum I'll call it p. So...shouldnt I have p_{1}+p_{2}=p? Furthermore, is the propagator...

Homework Statement Hey guys! So basically in the question I'm given the action S=\int d^{d}x \left[ \frac{1}{2}\partial_{\mu}\phi\partial_{\nu}\phi\eta^{\mu\nu} - \frac{m^{2}}{2}\phi^{2} -\frac{\lambda}{4!}\phi^{4}\right]. I have use the feynman rules to calculate the tree level diagram with...

In Feynman Lectures on Physics (you can find it online), chapter 33 of volume 1, the author derives Fresnel's formulas for the coefficient of reflection in an unusual way by making considerations about the different possible polarization of light. In this way he derives the squares of the...