Virtual Journal on QCD Matter

Up to now, the AdS/CFT duality has been used to model thermal transport processes in a strongly coupled gauge plasma (see the Review in this VJ). It was unclear what theories with an AdS/CFT dual predict for hard processes, for which QCD permits rigorous calculations. In several recent articles,

• Deep inelastic scattering at strong coupling from gauge/string duality: the saturation line
• Deep inelastic scattering off a N=4 SYM plasma at strong coupling
• Jet evolution in the N=4 SYM plasma at strong coupling

Hatta et al. have shown how such processes can be explored in strongly coupled super-Yang Mills theories with a gravity dual. (more…)

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The AdS/CFT duality has allowed theorists to calculate previously incalculable quantities in a strongly coupled gauge theory (see the Review in this VJ), albeit one with infinitely many colors. However, the theoretical magic comes at a price: The (N=4) super-Yang Mills (SYM) theory is conformally invariant while QCD has an intrinsic scale, which allows it to be simultaneous confining at long distances and weakly coupled at short distances. The strongly coupled SYM theory, in its purest form, has neither of these properties. What are the phenomenological consequences of this difference between the two theories with regard to quantities of interest to relativistic heavy ion physics? (more…)

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The recent post on the AMO competition for perfect fluidity offers a wonderful opportunity to compare and contrast the techniques of condensed matter physics versus those of relativistic heavy ion physics. (more…)

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In April of 2005 Brookhaven National Laboratory announced that scientists at RHIC had created the most ideal liquid ever observed in nature. Now, 3 years later, RHIC is facing competition to this claim from strongly interacting ultra-cold Fermi gases. (more…)

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Collisions of heavy nuclei at RHIC (and soon LHC) energies create a state of matter similar to that of the early universe a few microseconds after the big bang, characterized by a temperature of T ~200-400 MeV. Temperature is one useful intensive thermodynamical variable for depicting the phase diagram of nuclear matter. Another is the net baryon density ρ_B (or alternatively, the baryon chemical potential μ_B), reflecting the fact that baryon number is a conserved quantity. The central region of a collision at RHIC is nearly (net!) baryon free, with a value of μ_B/T ~10% << 1, and therefore crudely approximates the early universe, where this ratio was of order 10^-9.

As exciting as it is to explore the early universe in the laboratory, very relativistic nuclear collisions access only a ‘small’ region of the phase diagram near μ_B =0. There is also enormous astrophysical relevance along the μ_B axis very near T=0. This is the domain that describes nuclear matter as found in neutron stars. (more…)

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The idea that superstring theory may help inform the physics of relativistic heavy ion collisions begins with Maldacena’s remarkable discovery in 1997 that the (N = 4) supersymmetric Yang-Mills theory in (3+1)-dimensional space-time and 10-dimensional superstring theory in a geometrical background composed of the product of 5-dimensional Anti-deSitter space (AdS) and a 5-dimensional sphere describe the same physics. (more…)

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Microscopic transport models aim at describing the time-evolution of a heavy-ion collision, either in part or from beginning to end, using microscopic degrees of freedom, i.e. nucleons, hadrons or quarks and gluons. They are based on the solution of a transport equation, which can be derived within the framework of kinetic theory. (more…)

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