All Questions
11
questions
1
vote
0
answers
75
views
How do we measure the gluon scattering?
In QFT, we often calculate the 'Feynman amplitude' for gluon scattering. As we know, Gluon is gauge boson mediating the strong force between quarks. By color confinement, Quarks are never seen in our ...
- 108
0
votes
0
answers
61
views
Calculating Diagrams with Wilson Lines to One Loop
I have a question concerning the calculation of amplitudes containing Wilson lines.
I want to calculate the jet function defined by equation (3.3) from this paper.
$$\mathcal{J}(\text{arguments})u_s(p)...
- 2,983
2
votes
0
answers
92
views
Why does a gluon soft factor depend only on the adjacent legs?
The gluon soft factor can be obtained by taking the soft gluon limit in the $n$-point MHV amplitude $$A(1,2,\cdots, n)=\frac{\langle i,j\rangle^4}{\langle 1,2\rangle\cdots\langle n, 1\rangle},$$ to be ...
- 302
2
votes
0
answers
38
views
How to derive Collinear amplitude proportional to Born amplitude
In the collinear limit, the squared matrix element factorises into (for partons 4 and 5 going collinear)
\begin{eqnarray}
\overline{\sum}|M_3(1+2 \to 3+4+5)|^2 \approx \overline{\sum}|M_2(1+2 \to 3+4')...
2
votes
1
answer
80
views
Is Compton Scattering the "Abelian limit" of $qg \rightarrow qg$?
I have calculated the average over initial and sum over final states of the squared amplitude for both Compton scattering $e^-\gamma \rightarrow e^-\gamma$ (QED) and quark-gluon scattering $qg \...
- 321
3
votes
1
answer
244
views
$qg \rightarrow qg$: Spinor Helicity Formalism
I am calculating the cross-section for quark gluon to quark gluon scattering in the spinor helicity formalism. This process has contributions from the Mandelstam channels $s$, $t$ and $u$.
Using the ...
- 321
1
vote
1
answer
133
views
Confusion among channel $u$ and channel $t$ in exclusive reactions
In the this paper (https://arxiv.org/abs/1203.4392), on page 2 it is said that
Since DVCS amplitude is symmetric under $s \leftrightarrow u$ channel crossing, the CFFs and $^{S}C^i_{\cdots}$ ...
- 1,597
4
votes
0
answers
222
views
Asymptotic states in strongly-coupled QFTs
In QFT the asymptotic states play a very important role, as they are the basis on which we decompose our in-states and out-states when we calculate correlation functions.
However, I have not been ...
- 431
4
votes
0
answers
527
views
Ghosts use in the calculus of the scattering matrix
When you perform the calculus of $S$ matrix in, for instance, QCD maybe you need to add ghosts in external legs or internal loops. E.g.: $q\bar{q} \rightarrow gg$ needs 2 ghosts diagrams with ghosts ...
- 1,597
4
votes
1
answer
219
views
The kinematic region for the operator product expansion
In Ch.18 of the textbook An Introduction to Quantum Field Theory by Peskin and Schroeder, on P.613 the operator product expansion (OPE) is introduced
$$\mathcal{O}_1(x)\mathcal{O}_2(0)\to \sum_n C_{...
- 962
9
votes
3
answers
950
views
Are there any serious alternatives to QCD nowadays?
I've read several posts here where people talk about the history of the developement of the theory of strong interactions. And they mention Regge theory, pomerons, S-matrix and so on.
I'm confused ...
- 5,569