Talk:Quantum chromodynamics/Archive 1

Untitled
Hey you guys! Jack Steinberger, who won the Nobel Prize for discovering the muon, emailed into OTRS with great praise for your work. I'm copy/pasting his comments:


 * "Dear Wikipedia, I want to thank you and to compliment you on your service. I often use it, especially also for technical information in physics and astronomy. Just now I was impressed by the density of information in youyr article on QCD, the theory of the strong interaction, in particular, its history. Jack Steinberger, Nobel Laureate, Physics, 1988."

In another email he wrote:


 * "I am enormously grateful for the fantastic, free service Wikipedia provides; I don't see how it is possible [...] With best wishes, and thanks for what you do, Jack Steinberger."

As a scientist myself, I often hear about the high quality of Wikipedia's science articles from PhDs, professors, graduate students, and others. I'm happy to be able to share another testament to your awesomeness.

Duplicate Merge
We just made a duplicate page redirect here, here is the content, I don't know if there's anything which needs to be merged in:

Quantam Chromodynamics, or QCD, is a relavistic quantam-mechanical quage theory of the strong interactions based on the exchange of mass-less gluons between quarks and antiquarks.

QCD is analogous to quantum electrodyanmics (QED) in the field theory of electromagnetic interactions, but with gluon replacing the photon and the 'color' quantam number instead of electric charge. The theory has been tested successfully in high-energy experiments involving muon-nucleon scattering and proton-antiproton collisions.

(by User:Vholiday), fabiform | talk 02:21, 3 May 2004 (UTC).

Contradictions ! - Color confinment is an illusion.
... color charged particles (such as quarks) cannot be isolated singularly ... When two quarks become separated, as happens in particle accelerator collisions ...

What is the meaning of the word separation ? Acting separately ? Having distinct properies ? Or exist separately at some greater distance ? What is the distance constraint ? What is the action constraint ? What is the concept of separation in QCD ? If some force is strong, an you are not able to separate constituents, does it mean total confinment ? Maybe confinment of thinking. In nuclear particle interactions, quarks are changed or exchanged, according to the main stream theories. What is the cause of effect in interactions, if color force prohibts quark separation. If separation, or separate action, is possible, there is context of this separation and separate action. If it is not, the meaning of the quark is redundant, because it is just effect of other, more fundamental entity, and quark is a view of that entity. What is the size of the quark ? Where is the boundary of "cannot be isolated singularly" and "two quarks become separated" ? Does the QCD theory do not recognize the time and space scales ? Do the word "detected" means "detected by human detectors" or "exist as real entity in nature" ? Color confinment is an illusion. Color confinment violates both, the causality and energy conservation. If color force "is constant, and does not decrease with increasing distance", where did the energy for this come from ? What is the integral of such force of particle ? Is color force isotropic ? Color confinment means deterministic creation of quark-antiquark pairs. The speed of this creation must deterministicaly reflect the relative speed of quark-quark, in both directions. That means controling the quark-antiquark creation and annihilation. And we are back. What are conditions for the dynamics of quark-antiquark creation and annihilation ? What is stability of such structures ? What if some quark-antiquark in chain annihilates sooner than the cause causes the anticause ? The state of the cause (quarks) is instantly interconnected with the state in the space between the quarks. What is the spacetime layout of such structures, especially in the context of quark motion at relativistic speeds. Total violation of causality ! Is this physics or Lego for children ? Pardon - Lego is causal ... Softvision (talk) 00:10, 14 July 2009 (UTC)

Non-neutral
Previous versions of this entry were non-neutral in favour lattice theory and I tried to mitigate this. It seems I may have undone some alterations which was inadvertent and unexpected?!?

Poor grammar causes confusion
If I knew more about this subject, I would try to make the correct changes myself, but I am not so lucky.

The second sentence in this article doesn't make any sense:

"Because of its special property [property], it was first proposed in the early 1970s by [people]"

This means that QCD was proposed because of this property. It doesn't seem right that the property itself didn't spark the proposal, and if by some strangeness, it did, that should be explained.


 * I apologize, I'm not a native speaker and "Because of its..." is my sentence. But could you explain your objection more comprehensibly? I am simply not understanding what can be unclear about the sentence. QCD exhibits asymptotic freedom, and this is the only good reason why it was proposed as a description of the strong interaction. It explained the experiments, Bjorken scaling, and so forth, that indicated that the quarks are "free" at very short distances. This behavior of quarks - suggestive of free particles - was the only good justification for introducing the non-abelian theory and gluons, and therefore the discovery of asymptotic freedom was essentially identical to the discovery of Quantum Chromodynamics, and this is why these three men got the Nobel prize today.--Lumidek 15:00, 5 Oct 2004 (UTC)


 * I'd suspect that the objection is that for QCD to have the property asymptotic freedom QCD must already exist and if it already exists it can't be proposed. While not incorrect, the sentence doesn't communicate the relationship between the two or the significance (i.e. that by having the then unique quality of asymptotic freedom QCD could effectively describe the strong force, which other theories could not do.) VermillionBird 16:45, 2005 Mar 9 (UTC)

This sentence's poor grammar also makes it hard to understand:

"According to this theory, there is [noun phrase] and that [noun] are [noun phrase]."

The "that" doesn't seem to fit.

Heavy flavors

 * In many applications of QCD one can ignore the heavy flavors (charm, bottom and top)

The text is unclear. This is the only reference to charm, bottom, and top. Why are they heavy? What are the other three flavours called? Why are they called these names? ("charm" is kinda sweet)


 * Charm, bottom and top are the three heaviest flavors of quark. You can read more about them on the page about quarks or the page about flavour (particle physics). Each quark flavor has a particular mass and these three just happen to be the heavy ones. The other three flavors are up, down and strange.


 * The names are weird historical artifacts: Up and down are so called because they differentiate between different isospins of particles. If you think of isospin as being a real spin rather than just a flavor number, then naming the different ones up and down makes some kind of sense. The strange quark is so named because particles containing strange quarks have long lifetimes, which physicists at the time thought was strange. The charm quark is so named either because Glashow thought the charm quark would be the charm that won him the Nobel, or because people thought the notion of a two sets of two quarks would be charming. Though, from looking at Glashow's paper on the subject, it seems that he just picked the letter C because it came after B for baryon. Bottom and top are so named to match down and up. -- Xerxes 17:19, 2005 September 1 (UTC)

wait a minute!
Okay, let me get this straight. According to this article, the attraction between quarks does not diminish with distance, therefore, it would take an infinite amount of energy to separate them. Here are the problems as I see them:

1)it would take an infinate amount of energy from the quarks themselves. 2)they dont seem large enough to have a force of that magnitude apply to them. 3)wouldn't there be a particle by neccecity for the force according to the laws of quantum theory? (a.k.a. all particles can be intepreted as waves, and all waves as particles) 4)If such a force existed, wouldn't all the quarks squeeze together into one big mush?

a point in favor:

1)could this actually account for inertia? quarks make up everything, and if it is all one big mush, then maybe inertia is just us rearranging the quark mush and they are exerting preassure against us?

Arakanuva 23:46, 5 September 2005 (UTC)arakanuva


 * 1&2) You don't actually separate quarks this way; it's impossible.
 * 3) Yes, it's called the gluon.
 * 4) Yes, they form hadrons like the proton and neutron.


 * 1) No, quarks that are close to one another feel little force. In their natural low-temperature state, they just form protons and neutron that live happily in the nuclei of atoms. Unless you hammer the nucleons really hard, you'd never know about the quarks at all. -- Xerxes 03:09, 2005 September 6 (UTC)


 * 1) Suppose you try to separate two quarks forming an hadron. You have to give energy to do this and as they get further, more energy is needed. It reaches a point that there is so much energy accumulated that it would be possible to create out of the vaccum a quark-antiquark pair, that form with the original quarks we had another two hadrons. —The preceding unsigned comment was added by 83.33.68.89 (talk) 03:10, 1 February 2007 (UTC).

Grip on reality
I think the introduction to this article can be made more accessible to non-specialists. The present introduction contains too much technical information without describing to a layperson what the strong interaction is. I know all the relevant links are present in the introduction, but perhaps a few words about QCD being a description of the stong interaction, which is a nuclear force etc. could be mentioned. Also, some of the links themselves aren't that great either: for example, a gluon is described on that page as a vector gauge boson that mediates the strong colour charge interactions of quarks in quantum chromodynamics !!! This suggests that some of the other technical articles can be made slightly more accessible to non-specialists. MP  (talk) 12:02, 27 December 2005 (UTC)


 * That's what a gluon is. I don't see what's so confusing about that. A reader unfamiliar with any of those terms can click on the associated links. Can you be more specific about what you find confusing? -- Xerxes 16:24, 27 December 2005 (UTC)

Hi Xerxes.

All I meant was that the introduction (to this and other articles) could be made more accessible to non-specialists by adding a few more (less technical) descriptive words. Regarding the definition of the gluon, I know that the definition given is correct, I'm just saying that it could be made less abstruse by a few more words of explanation at the start. The beginning of an article is most important; if the reader's attention isn't grabbed at the start (by not understanding what is meant, and especially if they have to click on several links just to make sense of the first sentence in the article), then they will be turned away. I agree it's not always easy to do this in the nmore technical articles, but I think we should make the effort. MP  (talk) 10:05, 28 December 2005 (UTC)


 * Well, admittedly I'm completely biased by being an expert in this field, but here's my perspective: We're not advertising QCD. If people have clicked on a link or searched for the term, they must already be interested in the subject. Then we Wikipedia editors should present them with an article that is (in order of importance) 1) correct, 2) complete, 3) clear, 4) accessible. If we can make the article more accessible without making it less correct, complete and clear, I'm all for it. In practice, people attempt to be accessible by putting in nontechnical words that start out being unclear (because nontechnical words lack the precision of the correct terminology), then mutate into sort of a muddle of lengthy sort-of-correct hand-waving and then back into popular misconceptions. There are so many errors and omissions around that our time seems poorly spent rewriting paragrphs that are already correct.


 * Anyway, that having been said, I tried tweaking the abstract a bit yesterday. Better? Worse? -- Xerxes 14:51, 28 December 2005 (UTC)

I can see your point of view. I had similar problems when editing some of the general relativity articles; I'm from the other end of the spectrum and am trying to learn more about paricle physics. To a certain extent, we are advertising QCD and other theories; I've been guilty of falling into the trap of treating Wikipedia as a place to write articles solely for specialists. Take a look at the general relativity article, for example - several of us have worked hard at this article and it has only recently become more accessible to non-specialists without losing clarity and completeness. Perhaps it's in the nature of particle physics that there are so many technicalities. However, if there are more specialists editing the pages, then they are the ones who are most likely to present the material in a more accessible way without making it less complete and clear.

Anyway, yes, your tweaking was fine - I think it makes the intro. better. MP  (talk) 08:16, 29 December 2005 (UTC)

QCD comments
QCD is one of the most important but less studied fields in physics. Higgs field should be a part of QCD, but unfourtunatly, it isn't. It would be much more reasonable if it was.--216.183.184.253 01:33, 2 February 2006 (UTC)


 * Why should the Higgs be part of QCD, it was specifically invented as part of electroweak theory to give mass to the gauge bosons. Maybe you are referring to GUT, unifying electroweak and strong interactions?Jameskeates 12:17, 17 August 2006 (UTC)

I dont know but maybe the first comment refers to some models that explain the higgs boson with QCD-like theory, like technicolor or topcolor.


 * Can somebody (with a better understanding than I have) explain the factor 'g' in the Lagrangian? thanks —Preceding unsigned comment added by 152.3.182.117 (talk) 19:41, 10 September 2007 (UTC)

http://www.terra.es/personal/gsardin/news13.htm  comments--79.119.215.221 (talk) 22:12, 21 August 2011 (UTC)

Proof of confinement
Confinement is not necessarily a "property of QCD" as it is incorectly stated in the article. It is just a hypothesis, untill there is actually a proof (a derivation of confinement from the QCD lagrangian), which does not exist. Of cause, I believe in this hypothesis, as most physicists do. But it is still just that, a hypothesis.

olenal.

There may not be an analytical proof, but lattice studies do prove that QCD confines.

Do they? I think lattice results are still under discussion. Not every one agrees with that statement.

Yes, there is no strict proof, as you can not proof (in a strict mathematical sense!) that lattice QCD leads to the correct results. (Some issues include calculation in Euclidean space, taking the continuum limit, large distance behavior with dynamical quarks (after all quarks lead to string breaking) and universality of fermion actions used in Lattice QCD.) Notice that there is lots of other definitions of confinement on the market. One is simply to say that no colored objects are observed experimentally. So color confinement is a property of the real world and if one believes that QCD is the correct theory to describe the strong interaction (and there is overwhelming evidence for that) it has to be a property of QCD. (143.50.77.229 (talk) 07:33, 9 June 2009 (UTC))

Remove Lagrangian?
The section titled `QCD' which displays the Lagrangian seems a little pointless. To those who know QFT it is redundant, and to those who don't, I'm sure it's incomprehensible. I suggest removing it. Any objections? Shambolic Entity 04:20, 1 November 2006 (UTC)


 * I strongly disagree. Lagrangian is redundand to those who don't know what is a Lagrangian, and to those who wish to understand 'how QFT affects other aspects of life n science' only.
 * But many ppl read encyclopediae to understand 'what smthng looks like' in brief.
 * May be there's something that fits this purpose better, but many ppl surely wish to see L-n first (again, may be they aren't right in this particular case). —Preceding unsigned comment added by 83.237.111.35 (talk) 10:29, 21 October 2007 (UTC)


 * Yes, agree, I came to this article specifically to see what the Lagrangian looked like. —Preceding unsigned comment added by 130.246.135.176 (talk) 13:19, 6 July 2009 (UTC)

americanisations
please keep americanisations to a minimum, remember that this is an international website and therefore standard international english should be used, i will continue to fix this later but have only got as far as the first two columns —The preceding unsigned comment was added by Corvidaecorvus (talk • contribs) 15:10, 17 December 2006 (UTC).

Chiral Perturbation Theory
Chiral Perturbation Theory is not an effective model. It is the QCD effective theory at low energies. It is, QCD al low energy = ChPT.

Chiral Perturbation Theory is not an expansion around the quark mass equal to zero. It is a low energy expansion based on the spontaneus chiral symmetry breaking of QCD ,which is an exact symmetry when quark masses are equal to zero, but for the u,d and s quark, which have small mass, it is still a good aproximate symmetry.

Removed from article
A recent theory proposes to include gravity in Maxwell's equations and discards QCD entirely. In 2006, former NASA researcher Edwin Klingman proposed a fourth and final field, which he dubbed the "C-Field," (not the Fred Hoyle C-Field) as a fundamental field of the universe. Published in 2007 as The GeneMan Theory , its basic equation, F=q(E+vXB)+m(G+vXC), is recognizable as an extension of Maxwell's equation If Klingman's theory is correct, it obviates the need for quantum chromodynamics and for string theory. The theory don't appear to be notable (no peer review pubblications, and only this book). Similar edits occur in Dark matter, QCD matter and Standard Model, and should be checked.--Banus 09:53, 11 November 2007 (UTC)

Field tensor (a sign problem)
With the given choice of the covariant derivative it seems to me that there is a wrong sign in the nonlinear part of the field tensor. Pra1998 (talk) 15:01, 24 November 2008 (UTC)
 * In fact, in the German version of the article there is a +g ... instead of our -g .... However, actually the sign is perhaps irrelevant, since the Lagrangian contains g as 1/g2, and the mathematicians avoid g totally by writing $$\nabla \mathbf A={\mathrm d}\mathbf A +\mathrm A\wedge\mathrm A$$, i.e. without any g, where this article would use ... -g....


 * So, after all, the sign may be totally irrelevant, although sometimes ago I stumbled over the same question as you did. - Regards, Meier99 (talk) 15:11, 28 May 2010 (UTC)


 * This is an old discussion at the time there was no Gluon field strength tensor article, but for the record, the signs must of course be just conventions (both seem to be used in the literature, as suggested above anyway). M&and;Ŝc2ħεИτlk 09:40, 11 March 2013 (UTC)

Quark masses all the same?
The Lagrangian has "m" before $$\delta_{ij}$$ in one place. Surely this should be $$m_i$$ because it is the mass of the i'th quark and the indices i and j range over the quark flavours? —Preceding unsigned comment added by 130.246.135.176 (talk) 13:22, 6 July 2009 (UTC)

The Theta parameter?
Interestingly, the article makes no mention of the theta parameer in QCD. My knowledge on this aspect is at most anecdotal, but it seems to have possibly deep consequences (if it is nonzero) on CP braking and stuff. Moreover, it effectively appears in the Lagrangian, so someone coudl agree that the one presented is not the most general QCD Lagrangian possible. Would somebody be willing to add some information to the article? I would lvoe to finally read something consice and readable on these matters :) Jan Ebr —Preceding unsigned comment added by 78.128.198.193 (talk) 19:27, 1 September 2010 (UTC)
 * I support this proposal but also don't have enough knowledge in this topic.. RolteVolte (talk) 10:52, 27 September 2010 (UTC)

history has dates
Shouldn't the section called "history" have some more dates in it, just a year sprinkled here or there? —Preceding unsigned comment added by 96.224.168.139 (talk) 00:41, 10 January 2011 (UTC)

QCD is a theory, not a study
The first sentence of the article says QCD is a theory of the strong interaction. The second sentence says it is the study of "the SU(3) Yang–Mills theory of color-charged fermions (the quarks)". It cannot be both a theory and a study, so I'm going to remove the second sentence. My guess is the second sentence should be "It is an SU(3) Yang-Mills theory of color-charged fermions (the quarks).", but I'm not sure, so I'm just going to delete the sentence, which doesn't add anything anyway and is certainly wrong as stands. 190.161.134.30 (talk) 02:35, 1 July 2011 (UTC)

Assessment comment
Substituted at 15:37, 1 May 2016 (UTC)