The feynman-diagram tag has no wiki summary.
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Electron-Positron Scattering using the Feynman Rules - Integration Q
I'm doing independent studies on electron-positron scattering, specifically the annihilation diagram contribution to the M matrix in Bhabha scattering, and this is the equation I recovered with the ...
0
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1answer
31 views
How to verify gauge invariance of an amplitude
I have calculated a tree level amplitude for Compton scattering (${e\left(p\right)+\gamma\left(k\right)\to e\left(p\prime\right)+\gamma\left(k\prime\right)}$):
$${
...
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0answers
18 views
Reduced graphs and pinch-singular surfaces
I am reading a book on perturbative QCD by John Collins. In Chapter 5, the terms reduced graph and pinch-singular surface are used for the analysis of mass singularities. However, their meanings are ...
3
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1answer
74 views
Evaluation of QED amplitude with 1 external photon
I'm trying to compute the exact QED amplitude with one external photon. Suppose that the photon has 4-momentum $q$ and polarization $\varepsilon^\mu$.
Peskin and Schroeder (p318) claim that ignoring ...
1
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1answer
62 views
Symmetry factor of a second order four point function term of the $\phi^4$ theory
I am reading Cheng and Li. On page 9, it is written that the coefficient $\frac{1}{2 \cdot (4!)^2}$ for the second order term of the four point function becomes just $\frac{1}{2}$ for the following ...
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0answers
63 views
Field Strength Renormalisation in Peskin and Schroeder
In chapter 7 of Peskin and Schroeder they define the field strength renormalisation $Z$ for a quantum field to be the residue of the Fourier transform of the correlation function
$$\langle \Omega | ...
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0answers
32 views
Exact summation of a sub-class of diagram: do we know the exact solved problem?
In quantum field theories (to be relativistic, (non-)relativistic statistical or whatever), we have the powerful diagrammatic approach at our disposal. Most of the time we can not sum up all the ...
2
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1answer
67 views
Vacuum polarization in QCD and gluon bubbles
In analogy to QED, the following Feynman diagram is a diagram contributing to the vacuum polarization effect, leading to anti-screening, asymptotic freedom and running of the strong coupling constant. ...
2
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1answer
114 views
What does this feynman diagram represent?
This feynman diagram represents the elastic proton scattering of electrons.
The $e^-$ has an initial momentum $k$ and a final $k^\prime$.
The circle represents that the target(the proton that is) ...
2
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1answer
68 views
Feynman diagram for $\overline{K}\,\!^0$ antimeson production on the quark-level
I've recently stumbled upon a physics problem concerning $\overline{K}\,\!^0$ antimeson production. In this particular example, colliding a $\pi^-$ meson with a stationary proton yields a $K^0$ meson ...
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0answers
50 views
Formula for Symmetry Factor
In $\phi^3$ theory, are there any formula for determining the Symmetry factor as that is found for the $\phi^4$ theory in any standard book of Quantum Field Theory?
2
votes
1answer
84 views
Relation between symmetry factors
In $\phi^3$ theory, the generating functional for interacting field theory is given by:
$$ Z_1(J) = \sum_{V=0}^{\infty} \frac{1}{V!} \Big[ \frac{iZ_g g}{6} \int \Big( \frac{1}{i}\frac{\delta}{\delta ...
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1answer
185 views
Most general Feynman diagram
What is the most general Feynman diagram?
Srednicki, in his QFT book, says:
The most general diagram consists of a product of several connected diagrams. Let $C_I$ stand for a particular connected ...
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0answers
49 views
Helicity dependence in loop diagrams
I am trying to evaluate a diagram that looks like
The middle of the diagram is a fermion loop. I know that the coupling between the $Z^0$ and fermions depends on the fermions' helicities, so it ...
3
votes
1answer
90 views
Deriving Feynman Rules (with the presence of a gluon field strength tensor)
If I have a Lagrangian of the form:
$$ \mathcal{L} = k \bar{\psi} \varepsilon^{\mu \nu} \lambda^a \phi G^a_{\mu \nu} + h.c. $$
[where $\phi, \psi$ are fermions, $\lambda^a$ are Gellmann matrices, ...
3
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1answer
86 views
Four-gauge-boson vertex in non-Abelian gauge theories
In Peskin & Schroeder's book page 524, the following diagram is calculated for the gauge boson self-energy in order $g^2$:
In dimensional regularization, its contribution is given by
...
2
votes
1answer
74 views
What are the rainbow and ladder approximations in a solid state physics context?
All references I find talk about quarks and gluons, where I have only very limited knowledge about.
From it's name (rainbow) I guess it applies to fermions coupled to bosons and we're interested in ...
1
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1answer
160 views
Degree of divergence of a Feynman diagram
I am studying the degrees of divergence of Feynman diagrams. I feel that I miss something but I don't really understand what. Please apologize if this question is silly. Anyway.
As an introduction to ...
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3answers
452 views
What does this “Witten's Dog” Feynman diagram in Futurama episode mean? [closed]
In an old episode ("Mars University") of Futurama which is a TV show, a character named Professor Farnsworth was trying to lecture "Superdupersymmetric String Theory" and "Witten's Dog" to some ...
2
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1answer
126 views
Getting rid of double delta function in Feynman rules
[1]
A very simple example of feynman rule for scalar fields.
After computing the diagram i have got the following:
$$
-i(2\pi)^4g^2\int d^4q \frac{i}{q^2 -m^2c^2}\delta^{(4)}(p_1 - p_3 -q)
...
4
votes
1answer
231 views
One-loop $\phi^4$ theory in $d = 3$
I'm trying to calculate the 1 loop correction to the propagator in massless $\phi^4$ theory, in $d = 3$, just for fun. The diagram just looks like a straight line with a circle touching tangently to ...
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0answers
100 views
exercise books for Feynman diagrams [duplicate]
I know QFT at graduate level but I'll like to master the skill of working with Feynman diagrams. I'm looking for a book of solved exercises on this topic.
Specifically, I'm looking for the kind of ...
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0answers
60 views
Feynman Diagram for Interaction of Deuteron with Oxygen-16
I have to draw a Feynman diagram for the interaction of a deuteron with Oxygen-16.
The interaction is as follows:
$ d + {}^{16}O \rightarrow p + {}^{17}O . $
I am generally ok with Feynman ...
1
vote
1answer
187 views
Feynman diagrams in three dimensions
Is there such a thing as an extension of Feynman diagrams into three dimensions?
Canonical Feynman diagrams use one space and one time dimension to visualize processes involving elementary particles ...
1
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1answer
126 views
Two-photon scattering: colours
Is there a particular conservation principle that necessitates that the outcoming photon pair has the same frequencies as the incoming photon pair?
I'm thinking in particular of these Feynman-like ...
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0answers
140 views
How fat is Feynman’s photon?
According to my calculations, it is a lot skinnier than Airy’s photon, but still a whole lot fatter than a straight line.
So, how does a photon get from point A to Point B?
The ray optics ...
3
votes
1answer
267 views
Wick Rotation, interpretation of $\bar{p}^2$ vs the usual $p^2=m^2$
Suppose we use the metric $(+,-,-,-)$ thus the momentum squared is
$p^2 = p_0^2-\vec{p}^2 = m^2>0$
Defining $p_E:=\mathrm{i}\cdot p_0$ and $\bar{p}:=(\,p_E,\vec{p})$ with Euclidean norm ...
2
votes
1answer
321 views
What does the graviton-matter Feynman scattering diagram look like?
The question is in the title really. I know gravity + QFT is on shaky ground but I'm not looking for Feynman rules, just a schematic, if that is possible.
Edit 1: added possible diagram for ...
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0answers
58 views
Chirality when moving around legs in Feynman diagrams
Assuming one has the following term in a Lagrangian:
$$
g (\overline{A_R} B_L)(\overline{C_R}D_L)
$$
where A,B,C,D correspond to spin 1/2 Dirac particles and the subscripts $R$ and $L$ denote left- ...
3
votes
1answer
198 views
Scattering Processes in Scalar Yukawa Theory
I'm trying to compute nucleon-nucleon scattering in scalar Yukawa theory. Here we view a nucleon as a complex scalar field $\psi$ and a meson as a real scalar field $\phi$. They interact through ...
1
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1answer
372 views
Feynman Rules for massive vector boson interactions
I am stuck at the beginning of a problem where I am given an interaction term that modifies the regular QED Lagrangian. It involves the interaction between a photon field and a massive vector boson: ...
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0answers
169 views
An use of the Schwinger-Dyson equation
I was confused as to how the equation 10 on page 7 or equation 21 on page 8 of this paper http://arxiv.org/abs/1211.1866 was derived. Can someone explain from where does this come and what do the ...
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3answers
219 views
Is there a simple way to compute some physical constant from Feynman diagram statistics?
I've been playing around writing some software to generate Feynman diagrams for QED, respecting the vertex "rules" described here, and avoiding creating isomorphic duplicates.
So from a starter ...
2
votes
1answer
183 views
Scalar Field Theory Decay/Scattering
I have a few questions related to the following interaction Lagrangian (no use of crossing symmetry in the following) involving the uncharged scalar $\chi$ and the charged scalar $\phi$:
...
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2answers
395 views
Recipe for computing vertex factors in Feynman diagrams
I am currently studying quantum field theory from Srednicki. In class we have covered till chapter 14 and then skipped to IR divergences. So my knowledge of quantum field theory is limited to those ...
6
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1answer
183 views
SUSY, ways to boost Chargino/Neutralino production?
Does anybody know a good reference that works out the equations for the Chargino/Neutralino production cross section in SUSY? I'm trying to understand if there are any tricks for boosting the ...
3
votes
1answer
278 views
Feynman rules for SUSY
This might be an incredibly naive question, but I'm wondering if there are a set of rules for "translating" between Standard Model and SUSY. For instance, if I want want to go from a Standard Model ...
4
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1answer
341 views
Interpretation of derivative interaction term in QFT
I am trying to understand what a term like $$ \mathcal{L}_{int} = (\partial^{\mu}A )^2 B^2 $$ with $A$ and $B$ being scalar fields for instance means. I understand how to draw an interaction term in ...
3
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1answer
313 views
Feynman diagrams and Hartree-Fock
I am puzzled by some lines I read in Mattuck's book on Feynman diagrams in many-body problems ( http://www.amazon.com/Feynman-Diagrams-Many-Body-Problem-Physics/dp/0486670473 )
Page 21 (1.14) for ...
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2answers
174 views
Is single photon annihination of electron-positron pair prohibited by Feynman diagram analysis?
It is obvious that electron-positron pair cannot annihilate to a single photon which will violate the momentum conservation. My question is can we get this knowledge from Feynman diagram or ...
1
vote
1answer
161 views
Diagram-like perturbation theory in quantum mechanics
There seems to be a formalism of quantum mechanics perturbation that involve something like Feynman diagrams. The advantage is that contrary to the complicated formulas in standard texts, this ...
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3answers
398 views
What makes a Feynman diagram real or virtual?
Simple question: as the title says, what makes a real Feynman diagram real, and what makes a virtual diagram virtual? Or in other words, how do I tell whether any given diagram is real or virtual? ...
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2answers
660 views
Gentle introduction to twistors
When reading about the twistor uprising or trying to follow a corresponding Nima talk, it always annoys me that I have no clue about how twistor space, the twistor formalism, or twistor theory works. ...
5
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1answer
154 views
Two-loop regularization
Working out some quantum field theory computations, I have to find out the value of the two-loop Feynman integral
$$
...
2
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1answer
214 views
4th order feynman-diagrams for $e^- + \mu^+ \to \nu_e + \bar{\nu}_\mu$
The task is to draw the two 4th-order Feynman diagrams of:
$$e^- + \mu^+ \to \nu_e + \bar{\nu}_\mu $$
I drew the first one as (time left->right):
...
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2answers
501 views
How do we distinguish between virtual particle exchange and particle decay?
The difference between virtual particles and unstable particles is discussed at length in this question (namely, virtual particles correspond to internal lines in Feynman diagrams and are not ...
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3answers
407 views
MVH amplitudes and the unitarity method
In the last 5 years there has been a silent revolution in QFT called the unitarity method and the Maximum Violating Helicity (MVH) Amplitudes that basically consist an alternative way to obtain the ...
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1answer
120 views
weak bosons and feynman-stueckelberg interpretation
from Wiki "The W bosons have a positive and negative electric charge of 1 elementary charge respectively and are each other's antiparticle."
Q:If each is the other's antiparticle then which is ...
2
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1answer
143 views
Photon-photon scattering matrix element
I have to write the matrix element $i\mathcal{M}$ given the Feynman rules of QED for the $\gamma \gamma$ scattering as the example above. Suppose that time is the vertical. There are two times, $t, ...
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Why did Feynman's thesis almost work?
A bit of background helps frame this question. The question itself is in the last sentence.
For his PhD thesis, Richard Feynman and his thesis adviser John Archibald Wheeler devised an astonishingly ...
