All Questions
29
questions
5
votes
1
answer
76
views
$ \pi^0\to \gamma\gamma$ parity conservation
Let's consider the decay process $\pi^0\to \gamma \gamma$. After we spontaneously broke the chiral symmetry of QCD coupled to an abelian gauge field $A^\mu$, we end up with the Goldstone boson ...
- 357
1
vote
0
answers
77
views
What is the meaning of twist in OPE?
In Operator Product Expansion (such as explained in Peaking) there appear a quantity for an operator called twist, defined to be $d-s$ where $d$ is the scaling dimension of the operator and $s$ is it'...
- 41
0
votes
0
answers
52
views
Using Compton scattering to derive the deep inelastic cross-section for the parton model
In the second volume of The Quantum theory of Fields, Weinberg provides the inelastic cross-section for the scattering of an electron from a nucleon with four momentum $p$ based on the parton model:
$$...
- 163
-1
votes
2
answers
206
views
How exactly does a proton form from quarks? What is the exact sequence and mechanism?
What are the steps that lead to the bonding of two up quarks and one down quark into a proton? For instance, does an up quark "bind" with a down quark in quark-gluon plasma, which then binds ...
- 29
1
vote
1
answer
81
views
How can I show the following contraction of the electromagnetic field strength and its dual? [closed]
Given the electromagnetic field strength $F^{\mu\nu}$, and its dual $$\tilde{F}^{\mu\nu} =\dfrac{1}{2}\varepsilon^{\mu\nu\alpha\beta}F_{\alpha\beta},$$
how can I show that
$$\tilde{F}^{\mu\nu}F_{\nu\...
2
votes
0
answers
77
views
Transpose of a matrix element [closed]
A matrix element is just a number. Now, If I have the following matrix element:
\begin{equation}
\newcommand\bra[1]{\left<{#1}\right|}
\newcommand\ket[1]{\left|{#1}\right>}
A = \bra{B}\bar{b}\...
- 41
0
votes
0
answers
41
views
Structure function in DIS calculation step
There is one step in the calculation that I am not understanting, but there are many things to present so one can understand and help me:
i)$k^2$ and $k_T^2$ are small, so can be neglected;
ii)$k^\mu=\...
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
2
votes
0
answers
155
views
Can one distinguish QED (or QCD) from QED (or QCD) plus higher field powers?
The Lagrangian of QED is based on minimal coupling; it contains a term proportional to $F_{\mu\nu}F^{\mu\nu}$ for the electromagnetic field.
The QED Lagrangian is the simplest Lagrangian with U(1) ...
- 684
2
votes
1
answer
814
views
Topological theta-term as a background electric/magnetic field?
The topological $\theta$-term in the Schwinger model (1+1-dimensional QED) can be interpreted as a background electric field, as explained in Chapter 7.1.2 of Tong's lecture notes. The same holds true ...
- 1,783
2
votes
1
answer
461
views
Why is the fine structure constant the probability for photon emission by a charged particle?
I see in page 31 of Martin, Hanzel "Quarks and Leptons", that the fine structure constant is the probability for photon emission by a charged particle. Also I read from Lubos Motl's answer on this ...
- 700
3
votes
1
answer
692
views
Wilson Loops and Confinement in QED
In [1] Kenneth G. Wilson proposed a mechanism for confinement using lattice paths what leds him to the concept of Wilson loop. It seems to me that he is using mainly a single abelian field. He says
...
- 183
4
votes
0
answers
399
views
Is the physical mass of the electron a gauge invariant quantity?
In Lattice, one cannot calculate gauge non-invariant quantities, such as the quark mass. This is because one averages over the gauge and gets 0.
One way to get around the issue is to fix the gauge. ...
- 41
1
vote
1
answer
171
views
How would the photon having a charge change the electromagnetic interaction?
This question is motivated by my recent foray into Quantum Field Theory. Just to make this clear straight off the bat; I am not suggesting in any way shape or form that the photon has a charge. I am ...
- 703
1
vote
0
answers
302
views
Radiative correction to the charge form factor $F_1$ in QED
In QED, one can calculate the correction to the form factor $F_2$. To the lowest order, $F_1=1$ and $F_2=0$. At one loop, it is found that $F_2(0)$ receives a non-zero finite correction which is ...
- 26.8k