Feynman Definition and 649 Threads

My question is on the assumption that there is nothing in laws of nature that says if gravity had time reversal then nothing would appear odd. The example professor Feynman gave was a system with objects rotating due to gravitational attraction that rotated in a clockwise manner with normal...

I am not quite taking Engineering Physics yet, but in preperation for a future degree I would like to jump in with both feet and take a journey through physics using the master's lectures. I know i will be in over my head with the problems, but i am extremely passionate about the subject...

I know some people here hate the subject of virtual particles. So I will try to narrow my questions. Granted, virtual particles are just attempts to describe the math and are not real in and of themselves. But there seem to be a couple of different kinds of virtual particles (in the math)...

I used to think I understood this - big mistake! I've just watched a great classic Feynman lecture posted by another PF user (a superb way to spend 50 mins of you can spare the time) https://www.physicsforums.com/threads/i-found-the-best-teacher-of-physics.855335/ In that lecture, Feynman...

Homework Statement You received many steel balls of the same diameter d and container of known volume V. All dimensions of the container are much greater than balls diameter. How many balls can be placed in a container? Homework Equations (\frac{4}{3}\pi)(\frac{d^3}{8})\approx0,52d^3 The...

Hi! I've bought book Feynman lectures, Feynman exercises and Physics Jay Orear. Is worthwhile to buy Landau and Lifshitz books? I'm beginner in physics. I'm not sure what to school textbooks. School programme is too easy for me. I need more accurate source to learn physics. Although in my school...

http://www.feynmanlectures.caltech.edu/I_28.html#mjx-eqn-EqI283 It's Coulomb's law with retarded positions for the charges. Or something like that. How is it derived, please? Oh, never mind. I found some nice instructive materials from U Texas.

Homework Statement For the reaction below draw three Feynman diagrams, one that proceeds through exchange of a gluon, one through a photon and one exchanging a weak W-Boson. ##\pi^0+\pi^0\rightarrow \pi^++\pi^-## Which diagram provides the dominant contribution for this reaction? Explain how...

Hi! I have found a note about Generating functionals that seems to be very direct. Since I faced a difficulty many times without solve it, I would like if anyone can explain me my troubles. You can fine the note here (link). In the following figure, the author describes the 3-point green...

Since August 2014 the Feynman lectures have been available free of charge. They are direct from Cal Tech online, so one may rest assured they are not pirated. They are also available as a pdf download. Best introductory text I've found. The online site has better layout than the pdf, but is...

I am trying to learn about Feynman diagrams and am confused by some of the notation. In particular, what do matrices, in particular the Dirac adjoint, have to do with Feynman propogators and why are they in imaginary terms?

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...

I am wondering if anyone has experience in using IBP( Integration by parts) identities in the evaluation of Feynman diagrams via differential equations? My question is that I can't seem to understand where equation (4.8) on P.8 of this paper: http://arxiv.org/pdf/hep-ph/9912329.pdf comes from...

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!

So this isn't a homework problem really, but based on the posting rules for the HEP section this seems to fit better here. My issue is that I'm trying to use a Feynman diagram to represent a Bremsstrahlung process in which a vector particle is produced: $$ Z + e^- \rightarrow Z + e^- + v. $$...

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?