All Questions
7
questions
1
vote
2
answers
173
views
Why are two gluons needed for Feynman diagram?
Why do we need two gluons for the decay $$\pi^-+ p\rightarrow\pi^-+n+\pi^+\:\:?$$
If we have always the gluon $$\frac{1}{\sqrt{2}}(r\bar{r}-g\bar{g})$$ it should be possible with only one gluon
...
- 425
2
votes
3
answers
698
views
Do quarks annihilate into photons or virtual gluons?
I initially assumed a quark and its anti quark would annihilate into 2 photons (like electrons with positrons) and this does seem to be the case at least sometimes (e.g. For $\pi^0$s).
However in our ...
- 2,604
1
vote
1
answer
368
views
Deep inelastic scattering (DIS) and handbag diagram
Here, in page 11, you can see the so-called 'handbag' diagram that explains how a virtual photon emitted in a deep inelastic scattering (DIS) process interacts with a parton.
I'm going to use this ...
- 1,597
2
votes
1
answer
954
views
complicated QCD Color factor formula?
I was doing higher order calculations for purely gluonic system and came across complicated color factors like the product of six structure constants product $f_{a_1a_2a_3}f_{a_4a_2a_7}f_{a_7a_8a_1}f_{...
- 21
2
votes
2
answers
2k
views
Quark anti-quark pair creation. Do we need a gluon?
What is the difference between these diagrams?
Is the presence of the gluon taken for granted in the second one?
and
EDIT: I just zoomed into the picture, it is not a single quark state. There's a ...
- 24.9k
11
votes
2
answers
4k
views
Deriving Feynman rules from a Lagrangian for vertex factors for "more complicated" interactions
I am trying to derive Feynman rules from a given Lagrangian and I got stuck on some vertex factors. What for example is the vertex factor that corresponds to the four-scalar interaction that is ...
- 111
1
vote
0
answers
480
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 ...
- 1,701