Quark-gluon plasma

Quark-gluon plasma is a superheated, high-density mass of quarks and gluons which is believed to have existed during the first 20 or 30 microseconds of the Universe's existence. In such a mass the conditions for asymptotic freedom would hold, and as a result, confinement would become irrelevant. This is believed to be the only way that free quarks could exist. It is named by analogy with traditional plasma in which normal bonds between electrons and nuclei are broken.

It is also called the deconfining phase of QCD.

Its existence has been tentatively confirmed by results obtained at Brookhaven National Laboratory's Relativistic Heavy Ion Collider (RHIC). The current (April 2005) consensus of the four RHIC research groups is that they have created a quark-gluon liquid of very low viscosity. However, contrary to the widespread assumption, it is yet unknown from theoretical predictions whether the QCD "plasma", especially close to the transition temperature should behave like a gas or fluid. Authors favoring the weakly interacting interpretation derive their assumptions from the lattice QCD calculation, where the entropy density of quark-gluon plasma approaches the weakly interacting limit. However, since both energy density and correlation shows significant deviation from the weakly interacting limit, it has been pointed by many authors that there is in fact no reason to assume a QCD "plasma" close to the transition point should be weakly interacting, as like electromagnetic plasma (e.g. [1]).

It has also been hypothesized that the tentatively observed QCD fireball at RHIC may itself be the analog of a micro black hole. The results will be published across a number of papers in the journal Nuclear Physics A.

External links

• Horatiu Nastase The RHIC fireball as a dual black hole BROWN-HET-1439, Jan 2005. 10pp. e-Print Archive: hep-th/0501068
• BBC article mentioning Brookhaven results
• Physics News Update article on the quark-gluon liquid, with links to preprints