All Questions
18
questions
1
vote
1
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265
views
Why there is only $t$-channel for $u+\bar d\rightarrow u+\bar d$ scattering?
I am reading Griffith's textbook on particle physics about the $u+\bar d\rightarrow u+\bar d$ scattering for QCD. On page 285, it says there is only one possible channel ($t$-channel):
Why there are ...
- 1,783
2
votes
0
answers
38
views
How to derive Collinear amplitude proportional to Born amplitude
In the collinear limit, the squared matrix element factorises into (for partons 4 and 5 going collinear)
\begin{eqnarray}
\overline{\sum}|M_3(1+2 \to 3+4+5)|^2 \approx \overline{\sum}|M_2(1+2 \to 3+4')...
0
votes
0
answers
54
views
Evolution of the proton without external interactions
I've been thinking about the possibility of the proton evolving without external interactions and came up with the following problem. Let's say we have an isolated proton and therfore the Lagrangian ...
- 1,597
1
vote
0
answers
147
views
Soft-gluon of scattering amplitude
The question from Scattering Amplitudes in Gauge Theory and Gravity page 46, equation (2.120) from which I can't get a consistent formula.
I just calculate A3(gff) which two fermion and one gluon $A_n\...
- 11
2
votes
1
answer
80
views
Is Compton Scattering the "Abelian limit" of $qg \rightarrow qg$?
I have calculated the average over initial and sum over final states of the squared amplitude for both Compton scattering $e^-\gamma \rightarrow e^-\gamma$ (QED) and quark-gluon scattering $qg \...
- 321
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
0
votes
0
answers
99
views
Deep inelastic electron-proton scattering amplitude
In 'QCD and collider Physics' book by Ellis, Stirling and Webber, chapter 4.2 'The parton model from field theory' there is this equation for the amplitude of the process $e^- (k) P \rightarrow e^- (k^...
- 1,597
1
vote
1
answer
133
views
Confusion among channel $u$ and channel $t$ in exclusive reactions
In the this paper (https://arxiv.org/abs/1203.4392), on page 2 it is said that
Since DVCS amplitude is symmetric under $s \leftrightarrow u$ channel crossing, the CFFs and $^{S}C^i_{\cdots}$ ...
- 1,597
1
vote
1
answer
215
views
Elimination of three gluon vertex
I am reading this paper by Dixon, where it is mentioned that one can diagrammatically compute the colour factor of certain Feynman graphs, such as shown in figure 1, where they expand a three gluon ...
- 302
3
votes
0
answers
70
views
Polarized structure functions and Bjorken sum rule
I'm trying to understand what the Bjorken sum rule and the polarized structure functions entering it are. I will use equation (2.3) here as a reference for asking the question.
In Peskin, I've only ...
- 2,921
3
votes
0
answers
356
views
Bjorken Scaling and the Parton Model
It is often said that Bjorken scaling of the deep inelastic structure functions
\begin{equation}
\nu W_2(\nu ,Q^2)\rightarrow F(x)
\end{equation}
(where $Q^2$ is the virtuality of the photon, $\nu=\...
- 2,270
7
votes
1
answer
276
views
What is the mathematical motivation for complexifying momenta in BCFW?
One of the first steps in obtaining the on-shell BCFW recursion relations is complexifying the momenta of the external particles. Now complexifying things is not unprecedented (the dispersion program ...
- 1,124
3
votes
0
answers
194
views
Conversion of QCD cross section formula
I'm writing a program to calculate NLO cross sections for semi-inclusive high-$p_T$ pion production in proton-proton-collisions for my bachelor thesis.
I've got a paper describing the production ...
- 337
16
votes
4
answers
4k
views
Is forward scattering = no scattering?
What is forward scattering? If it is equivalent to no scattering, then why not call it "no scattering"?
- 5,569
19
votes
2
answers
3k
views
Why Cronin Effect Happens?
I'm looking for explanation on Cronin effect but unfortunately there's no Wikipedia entry or self-contained paper to start from. The statement of this effect is that:
"At leading order, multiple ...
- 1,707