Quantum-ChromoDynamics (QCD) is the quantum field theory believed to describe the strong nuclear force.
4
votes
0answers
55 views
No mixing in light cone perturbation theory
In hep-ph/0609090, Triumvirate of Running Couplings in Small-x Evolution, Kovchegov et. al. calculated the running coupling correction to the Jalilian-Marian, Iancu, McLerran, Weigert, Leonidov and ...
4
votes
0answers
230 views
Lattice QCD and the 5th dimension
I was digging into Nielson-Ninomiya Theorem and doubler fermions, as well as solutions to these problems using Domain Wall Fermions and overlap lattice fermions, both of which make effective use of a ...
3
votes
2answers
103 views
Is there something like Hawking radiation that makes protons emit component quarks?
If Hawking radiation can escape from black holes, could quarks perhaps become separated from protons despite it being "impossible" for that to happen?
3
votes
2answers
220 views
Polarization of the gluon
I think that, by now, it's understood that the gluon propagator in QCD has a dynamically generated mass. Ok, so my question is the following: where does the extra polarization degree of freedom come ...
3
votes
1answer
90 views
buiding circuits from color superconductors
caveat: the sort of exotic matter engineering in here is currently beyond the reach of our technology, but, that having been said:
Has their been any research on building models of these sorts of ...
3
votes
2answers
104 views
Playground of Forces
Why is it that the gravitational force acts on large sized objects while the strong and weak nuclear forces act at subatomic levels only? What is that stops each other to enter each others domain?
3
votes
1answer
77 views
Does the color of a quark matter in a meson?
QCD and confinement specify that hadrons must be color-neutral. My understanding is that this means you can have mesons (quark + antiquark) or baryons with 3 quarks, one of each color: ...
3
votes
2answers
139 views
Simulating a proton
How much computing power would it take to simulate a single proton from the bottom up, without taking any shortcuts whatsoever?
My current understanding is that:
A proton is basically a seething ...
3
votes
1answer
39 views
all multipolar terms of nuclear fields must be confined?
When usually speaking about QCD confinement, one refers to the fact that color charges over lengths above the hadron size are fully neutral, which implies that monopolar charges over an extended ...
3
votes
1answer
233 views
What's the deepest reason why QCD bound states have integer charge?
What's the deepest reason why QCD bound states have integer electric charge, i.e. equal to an integer times the electron charge?
Given that the quarks have the fractional electric charges they do, ...
3
votes
1answer
61 views
For mesons, or baryons, do sea quarks contribute to the angular momentum of the bound state?
The total angular momentum of a bound state of quarks, such as a meson say, can be done by studying the spin and orbital angular momentum of the 2 valence quarks.
What about the sea quarks why they ...
3
votes
0answers
49 views
Does the number of left handed chiral quark superfields always equal half the number of quark flavours?
In Weinberg's "The Quantum Theory of Fields Vol III" page 267 we're told that $n_f = 2N_f$. Where $n_f$ are the number of flavours and $N_f$ is the number of left chiral quark superfields (or the ...
3
votes
0answers
57 views
Final-state baryons in $p \bar p$ collisions in Pythia
I'm trying to simulate inclusive $\chi_c$ production in $p \bar p$ collisions at very low energies (~ 5.5 GeV) using Pythia8 event generator. Leaving aside problems bounded with applicability of ...
3
votes
0answers
134 views
Gauge invariance of gg->gg scattering amplitude?
I'm trying to calculate the spin and color averaged gg->gg cross section, and I am stumbling upon gauge invariance:
Must the amplitude not be invariant under replacements $\epsilon_i \to \epsilon_i + ...
3
votes
0answers
194 views
How to integrate over rapidity for Parton Luminosities in LHC?
I want to make a comparison of parton luminosities between Tevatron and LHC. According to Factorization theorem the cross section in hadron colliders, as long as the partonic cross section has $\hat ...
3
votes
0answers
216 views
Cusp anomalous dimension in QCD
What is the "cusp anomalous dimension", starting from the basics? I came across this term while reading some QCD papers.
3
votes
0answers
79 views
Can quark-gluon plasma ever be close to an ideal gas of asymptotically free quarks?
The question inspired by an upcoming colloquim at UCB.
A naive interpretation of quark asymptotic freedom seems to imply that at high enough energies they should be weakly interacting. On the other ...
2
votes
1answer
417 views
How much energy can be extracted from hydrogen?
http://en.wikipedia.org/wiki/B-L says that the difference between baryon number and lepton number is conserved. Ordinary hydrogen has one of each, but turning it into helium releases only the binding ...
2
votes
1answer
130 views
Similar masses and lifetimes of the $\Delta$ baryons
Why do the four spin 3/2 $\Delta$ baryons have nearly identical masses and lifetimes despite their very different $u$ and $d$ quark compositions?
2
votes
1answer
481 views
Lattice QCD and string theory
I've heard the claim that some aspects of string theory are used to improve Monte-Carlo simulations of lattice QCD, for example by people working at the LHC.
I know a bit about Monte-Carlo methods in ...
2
votes
1answer
132 views
SU(3) gauge invariance in QCD
In QCD, the gauge-invariant lagrangian under the trasformation
$ \psi \to \psi' = e^{ig T^a \theta^a(x)} \psi$
is written as:
$\mathcal{L} = \bar{\psi}(i\gamma^\mu D_\mu - m)\psi - ...
2
votes
1answer
106 views
Difference between Quark-Gluon Plasma and Color-Glass Condensate?
From the news. Apparently they are very similar, yet different.
2
votes
1answer
90 views
Parton Distribution Functions plot
I was looking at a plot of the parton distribution functions today and had a question. On the y axis, it seems like the value of x f(x) for gluons is greater than one at small x. I was under the ...
2
votes
1answer
208 views
Wilson loops and gauge invariant operators (Part 2)
These questions are sort of a continuation of this previous question.
I would like to know of the proof/reference to the fact that in a pure gauge theory Wilson loops are all the possible gauge ...
2
votes
1answer
127 views
Electromagnetic current-current correlators
Let the free electromagnetic current $J_\mu(x)$ be = $:\bar{\psi}(x)\gamma_\mu Q \psi(x):$ where $::$ is the normal ordering.
In this expression why is $Q$ thought of as a "charge operator" instead ...
2
votes
1answer
235 views
Axion related questions
I have several question regarding axion. Could anyone give me some brief introduction to what is a axion string, axion field and how is this related to fermion zero mode and chiral zero mode?
2
votes
0answers
60 views
CP-violation in weak and strong sectors
There is a possible CP-violating term in the strong sector of the standard model proportional to $\theta_\text{QCD}$. In the absence of this term, the strong interactions are CP-invariant. In the ...
2
votes
0answers
55 views
Cancellation of the quadratic divergence in QCD
I am currently reading about QCD in QFT-Peskin&Schroeder. When calculating 1-loop diagrams for QCD and using dimensional regularization, the 3-vertex boson loop, 4-vertex boson loop and ghost loop ...
2
votes
0answers
54 views
In a composite Higgs, should the Z0 decay at the same rate that the neutral pion?
I am sorry to ask a question that obviously is a sum of separate questions about a process: Should the decay rate of Z0 be related to the decay of the "higgs" composite field it is eating? And, should ...
2
votes
0answers
86 views
Macroscopic chromodynamics
Lately I've been reading about gamma ray lasing phenomena, and I've been wondering about the applications of this.
More concretely, the above fantastic question led me to wonder if we could somehow ...
2
votes
0answers
71 views
Does dark energy affect asymptotic freedom?
If the Hubble constant is extremely large, what will happen with quark confinement?
I guess that quarks will remain confined because of asymptotic freedom. But can gravity or dark energy have any ...
2
votes
0answers
110 views
What is new with quark-Gluon Plasma and the bubble formed at RHIC?
RHIC experiment results of forming Quark-Gluon Plasma and a possible bubble was news few months ago. I cannot find any follow up news after that. Does anybody know anything new in this front? I am ...
1
vote
2answers
90 views
The status of $SU(3)_C$ symmetry in the Standard Model
In the Standard Model of Particle physics the $SU(2)_{EW}$ symmetry and the $SU(2)$ isospin symmetry are broken. What about $SU(3)_C$? Is it broken too?
if YES, what breaks the symmetry?
If NO, what ...
1
vote
1answer
111 views
What are the problems in quark-gluon plasma? [closed]
Someone (T.D.Lee?) said that quark-gluon plasma would (after 1980?) be very important to understand high-energy physics experiments.
I read some description of this new state in wikipedia ...
1
vote
2answers
258 views
Is QCD free from all divergences?
On page 8 in http://arxiv.org/pdf/hep-th/9704139v1.pdf David Gross makes the following comment:
"This theory [QCD] has no ultraviolet divergences at all. The local (bare) coupling vanishes, and the ...
1
vote
3answers
83 views
Top quark production questions
I am just looking on the TopQuark production via proton antiproton collision and strong interaction. There seem to be three basic possibilities.
$q + \bar q \rightarrow Gluon \rightarrow t +\bar t ...
1
vote
1answer
88 views
QCD Parton Branching - Is the angle always negligible?
The GLAP equation describes the evolution of parton distribution under successive branchings. When branching takes place at a finite angle, the outgoing parton carries some finite transverse momentum. ...
1
vote
0answers
76 views
Glueball mass in non-abelian Yang Mills theory
How can the glueball mass be calculated in Yang Mills theory?
1
vote
0answers
58 views
Linear rising potential from a Gribov propagator
It is common wisdom that a gluon propagator (Gribov-)like
$$
G(p^2)=\frac{a+bp^2}{cp^4+dp^2+e}
$$
should give rise to a linear rising potential. So far, I have not seen a proof of this and I would ...
1
vote
0answers
88 views
Is the axial gauge with a $\xi$ term useful in Yang-Mills theory?
i) Do people use axial gauge with a $\xi$ term? When $\xi\neq 0$, ghosts do not decouple, but maybe it's still useful?
ii) Is it proved that the term $\frac 1 {2\xi}(n.A)^2$ in the Lagrangian does ...
0
votes
1answer
115 views
In a gauge theory, are two states related by a global phase transformation identified?
In a gauge theory (non-abelian for this question), I am told that two states $|\psi\rangle$ and $|\phi\rangle$ are to be identified if they are related by a gauge transformation $U(x)$
...
0
votes
1answer
65 views
Is There Any Difference Between Strong Quarks Force and Strong Nuclear Force?
the spectrum of quarkonium and the comparison with positronium potential for the strong force is:
$V(r) = - \frac{4}{3} \frac{\alpha_s(r) \hbar c}{r} + kr$
(where the constant $k$ determines the ...
0
votes
1answer
68 views
Has the mass of longitudinal and perpendicular spin 1 mesons been measured separately?
This might be a silly question. When the mass of a spin 1 meson is measured, is there a way to check whether it is the same for all polarizations? Is such a meson mass the same for longitudinal and ...
0
votes
0answers
101 views
Weak isospin and types of weak charge
My understanding is that QCD has three color charges that are conserved as a result of global SU(3) invariance. What about SU(2) weak? Does it have two types of charges? What I'm getting at is:
U(1) ...
0
votes
0answers
108 views
External ghost in QCD (specifically gluon-gluon scattering)
As a kind of followup question to my question of gauge invariance of gluon-gluon scattering (Gauge invariance of gg->gg scattering amplitude?), where I calculated gg->gg scattering with a unitary ...
0
votes
0answers
214 views
Quantum field theory notes by Preskill [closed]
In this "question" I propose typing into LateX of lecure notes by John Preskill, http://www.theory.caltech.edu/~preskill/notes.html.
Project could involve more people sharing the job. I think it is ...
-2
votes
0answers
49 views
Are Gribov copies responsible for the observed Mass-gap and color confinement properties of Pure Yang-Mills Theory?
New solutions to the existing problems are presented by the quantum mechanics and Einstein's theory of special relativity when treated together. The creation of particle/anti-particle pairs by quantum ...
-2
votes
0answers
45 views
What is equation of quark confinement, what is the process which called confined? [closed]
Quarks confined within larger particles such as proton, what is properties of quarks confinement?
why quark confined, anyway!?
divine purpose or what physical process?
-4
votes
1answer
228 views
Pion Decay and Fractional electric Charge disappeared, why?
Since the charged pions decay into two particles, a muon and a muon neutrino Fractional electric Charge disappeared, why?
The decay proceeds by the weak interaction $W^{+}$ and can be visualized in ...
-6
votes
2answers
245 views
Cramer's rule, Origin of Quarks Fractional electric charge? [closed]
In linear algebra, Cramer's rule is an explicit formula for the solution of a system of linear equations with as many equations as unknowns.
2u+1d=1
1u+2d=0
$$a_1d+b_1u=c_1$$ $$a_2d+b_2u=c_2$$ ...
