Talk:Quark–gluon plasma

For relativistic matter, pressure and temperature are not independent variables

Actually, what matters here is not whether the theory is relativistic or nonrelativistic, but whether the theory has conserved charges allowing us to have chemical potentials. The QGP states depend upon the temperature AND baryon number density. The pressure depends upon both the temperature and baryon number density.

Your last sentence is absolutely correct, but I'd wanted to avoid a discussion of μ_B here, in order to avoid the full QCD phase diagram. (That now finds its place in the QCD matter article). As for non-rel vs rel: it is relevant, since particle number is conserved in the non-rel case (text book stuff). I added a para in the chemical potential article to clarify (in any case, this para was needed there). Thank you for a very useful comment. Bambaiah 10:47, May 21, 2005 (UTC)

Unless there is some reason why this article is mostly arranged in a Q&A format, wouldn't it be better to write it normally? Dilbert 22:02, 17 March 2006 (UTC)

Broken Links

There are several broken links in this page. Someone should fix them. scienceman 19:02, 29 March 2006 (UTC)

Good stuff

I find the general introduction in Q and A very clear. Hail to the author! I even believe there should be more articles with the Q&A format.

Info D 12:03, 7 October 2006 (UTC)

Reference [1]

What is the meaning of the reference [1] ("may have been partially successful[1]. Currently,") ? Currently, it points to one of the SPS experiments, CERES, suggesting it was the one who was successful ? I'm not sure that physicists in this field will agree with that.

I suggest : the list of the final heavy ions experiments at CERN : http://newstate-matter.web.cern.ch/newstate-matter/Experiments.html

with the press release that the CERN issued at this time

(sorry for my bad english)

83.202.115.126 23:40, 17 January 2007 (UTC)

while lorentz contracted??

I found this extremely odd when reading, it striked me as not fitting in.

"The particles are then accelerated to ultrarelativistic speeds & slammed into each other while lorentz contracted."

If the "lorentz contracted" bit is correct, it should be wikified IMO, if not is should be removed.

Safety Concerns section

The new "safety concerns" section seems out of place here. The QGP itself is not a safety concern, it is a state of matter. If there are safety concerns about one possible mechanism for making QGP (namely the LHC) then they belong on the LHC page. The QGP does not consist of strangelets, and in fact has very little to do with them. Strangelets have net strangeness, while QGP (at least as made at heavy-ion colliders) has zero net strangeness. QGP is hot and strangelets are cold. They are different phases of matter. I think this section should be removed from this article. Dark Formal (talk) 02:46, 13 January 2008 (UTC)

Does the charge of a quark-gluon plasma need to be integral?

Or in other words, can you split a quark-gluon plasma into two pieces that cannot fully decay back into familiar particles without ending up with a free quark left over, i.e. requiring that these pieces represent one or more stable particles with very high mass and fractional charge?

Also, if the plasma must have a net integral charge, how would it "decide" where to break if, hypothetically, you had a large enough clump of it that you could split it in half before light could travel back and forth to each end? Wnt (talk) 23:04, 16 May 2008 (UTC)

For an infinite volume of QGP, the charge density must be zero, or else there would be infinite electrostatic energy costs. For a finite-sized volume, the charge must be an integer. Ultimately this is because the state as a whole must have zero color charge (like a big nucleus) to avoid infinite energy costs (a color-electric flux tube). That's a technical summary---feel free to ask for clarification. Dark Formal (talk) 03:05, 17 May 2008 (UTC)

Thanks for your answer! If you would, could you put a mention of the integer charge in the article (for a finite volume; the lay reader isn't expecting to encounter an infinite volume ;) ). It would also be nice to work in a wikilink for flux tube somewhere. Since this isn't my field and I don't have a source handy I'm leaving this to you, though. ;)

I'm still a bit confused about splitting the plasma in half, though. As the article says, it is not just a simple collection of free quarks, so I'm inferring that if you had a long rod-shaped mass of the plasma and found some "bullet" dense enough to blast it in half in a very short time, what happens is that the flux tubes are actually stretched out and eventually produce new quarks at the cut ends to maintain the required charge and color properties. But what confuses me about this is that in order for that to happen, this pattern of flux tubes needs to contain all of this information at the site where the break would occur. I suppose in the minimal-energy case you could have a "plasma" made up of some neutrons lying next to one another, and the tubes exist only to prevent a neutron from being chopped in half. But what happens in the high energy case when no distinct subentities exist - do you have one of these tubes running between every possible subset of two or three suitable quarks in the entire plasma? It seems like in order to cut such a plasma you might need to produce many times more particles than it contains, but I could be so wrong. Wnt (talk) 14:17, 17 May 2008 (UTC)

Sorry, I can't answer this in a simple way. The full answer involves the group-representation properties of large numbers of quarks. Analogy: you know that a group of electrons gives one combined electric field which is then "eaten up" by the appropriate number of positive charges. Simialrly, the quarks in one half of the QGP give one combined color flux which is just exactly eaten up by the rest of the quarks. Dark Formal (talk) 03:23, 18 May 2008 (UTC)

Color current?

I was wondering about "color current" in these plasmas. If you have a ring-shaped plasma of up and down quarks, and apply a strongly varying magnetic field, there should be some tendency to generate currents of up quarks and down quarks going in opposite directions - I think. (Since the up quark has twice the charge and half the weight I assume it would carry most of the current... figuring out the resistance of a ring of QCD plasma is another matter!)

Now, as I [(don't)] understand the QCD theory, the neutrons used to make up the plasma will each have had an up quark of any color at random, and by transferring gluons they could swap color with down quarks at any time. But even so a quark-gluon plasma made out of neutrons could have any number of up quarks with twice the number of down quarks... so there is a very good chance that not all quarks moving one way will have the same color. I've seen mention of color currents in reference to the "whitening" of the QCD plasma,[1] but having one running constantly sounds more (hypothetically) manipulable. At that point, well, I note that there is such a thing as chromomagnetism,[2] that papers about it seem to talk about quasiparticles, flavour symmetry breaking, S-wave tetraquarks and all kinds of groovy things, but the waters of my insight are rapidly sinking into the sands by this point. So I'll just ask: can you induce a color current in these plasmas and can you use it to apply a chromomagnetic force to things? Wnt (talk) 19:23, 1 June 2008 (UTC)

Rewrite

This article reads like a FAQ. I'd rewrite it myself to comply with standards, but I am not familiar with the topic at all. Momo Hemo (talk) 10:32, 8 August 2008 (UTC)