All Questions
52
questions
0
votes
0
answers
31
views
QCD parton shower hard scale
Currently I'm studying parton showers from QCD and I'm having trouble with understanding how the hard scale $Q$ is related to the virtuality and energy of the parent parton. The Sudakov factor $\Delta(...
- 291
1
vote
0
answers
52
views
Colour Factor in QCD Pair Annihilation
My question occurred when I was reading Introduction to Elementary Particles by David J. Griffiths. In chapter 8, part 8.5, he is calculating the colour factor of quark-antiquark annihilation.
My ...
- 81
2
votes
0
answers
50
views
When to consider and when not to consider the loop contributions from light quarks?
Consider the following Lagrangian:
$$
\tag 1 \mathcal{L} = \frac{\partial_{\mu}a(x)}{f}\sum_{q}\bar{q}\gamma^{\mu}\gamma_{5}q
$$
This is a Lagrangian of the axion-like particles (ALPs) $a$ interacting ...
- 8,901
0
votes
0
answers
140
views
Integral of the square of the spectral density in a quantum field theory
The quantity of interest is
$$
\int_0^\infty dE \, \rho(E)^2
$$
where $\rho(E)$ is the spectral density in a Quantum Field Theory. I am wondering whether
it has any physical meaning, and
it can be ...
- 1
1
vote
1
answer
233
views
Why Lambda Baryon and Sigma Baryon unequal sum isospin with "really" isospin?
For information isospin for $u$-quark = 1/2, isospin for $d$-quark = -1/2 and isospin for $s$-quark = 0.
Lambda Baryon consists $uds$ quarks,therefore sum isospin 1/2-1/2+0=0, It true.
But sum isospin ...
- 23
1
vote
0
answers
77
views
Energy stored in the gluon fields -- in a proton, versus, in a pure Yang-Mills mass gap
I was reading this How much of the proton's mass is due to the Higgs field? and finds the discussion says:
As Prof. Strassler explains in the link above, the proton mass is best throught of as ...
- 593
1
vote
2
answers
154
views
The ratio of the Higgs and QCD condensate contribution to valence quark masses
According to https://en.wikipedia.org/wiki/Quark#Mass, the quarks have the following masses.
I suppose these data in the table shows the valence quark masses, such that the uud valence three quark ...
- 4,336
4
votes
1
answer
182
views
Does QFT Imply Strings the Same Way that String Theory Implies Branes?
It is part of every introductory course on string theory (e.g. Tong) that the open bosonic string in $D = 26$ dimensions with Neumann-Neumann boundary conditions for directions $a \in \{0,\dots,p\}$ ...
- 196
2
votes
1
answer
182
views
Non-perturbative approach to high-energy physics
I know that main numerical approach to modeling high-energy physics events are Monte-Carlo event generators. But they are using perturbative description of collision and decay processes of particles.
...
- 343
1
vote
1
answer
109
views
Quark mass dependence of Glueball masses
In pure QCD, we have glueballs. Pure QCD can also be thought of as QCD where the fermion masses have been sent to infinity. If we vary the fermion masses (say, for simplicity, we deal with a single ...
- 6,896
0
votes
1
answer
185
views
How does the Nambu-Goldstone mode explain the absence of parity doubling?
I've been doing some reading about chiral symmetry breaking since it was not touched in my particle physics course
I found these slides
As explained in the above link, if we take $|\psi \rangle$ as ...
- 3,464
6
votes
1
answer
273
views
Photon-Gluon annihilation in QCD
I am starting to learn about QCD, and I wanted to calculate the squared matrix elements for photon-gluon annihilation into a quark and an anti-quark. However, I am having trouble writing down the ...
- 305
6
votes
0
answers
235
views
Which explanation of the OZI rule is correct (or most important)?
The OZI rule states that a QCD diagram is suppressed if it can be cut into two by only cutting gluon lines (the precise wording is addressed in the question What is the precise statement of the OZI ...
- 585
0
votes
1
answer
89
views
Color factor in Breit-Wigner formula
We are given the Breit-Wigner formula for the process $ud\rightarrow W\rightarrow e\nu$ as $$\sigma=\frac{1}{N_c^2}\frac{2J_W+1}{(2J_u+1)(2J_d+1)}\frac{4\pi}{s}\frac{\Gamma_{ud}\Gamma_{e\nu}}{(\sqrt{s}...
- 2,122
2
votes
1
answer
169
views
Does pionium decay in massless QCD?
The bound state of ${\pi}^+ {\pi}^-$ is called Pionium.
Is Pionium an Electromagnetic bound state or a Strong Force one? then Why?
Does such a bound state last forever if one works in QCD with ...
- 1,268