Theoretical High Energy Seminar – Niels Bohr Institute - University of Copenhagen

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Theoretical High Energy Seminar

Marco Panero (ETH Zurich)

Title: Thermodynamic properties of the QCD plasma and the large-N limit

Abstract: The heavy-ion collision experiments carried out at RHIC have provided convincing evidence that, at high temperature, hadronic matter undergoes a qualitative change to a new state, characterized by surprising features making it a nearly ideal fluid. While such `strongly interacting quark-gluon plasma' eludes a full analytical description based on the first principles of QCD, some of its properties can be predicted numerically by computer simulations, regularizing the theory on a lattice.

On the other hand, in recent years an alternative analytical approach to the dynamics of this strongly interacting system has been studied in string theory, through gauge/gravity models inspired by the AdS/CFT correspondence conjectured by Maldacena, and involving the mathematical simplifications that occur when the rank of the gauge group is taken to infinity.

In this talk, after introducing the physical problem of the QCD plasma and briefly discussing the lattice formulation for finite-temperature QCD studies, I shall present the results of my recent simulations of the equation of state in SU(N) gauge theories with N = 3, 4, 5, 6 and 8 colors, and their extrapolation to the limit for N going to infinity.

The results for the different gauge groups reveal that the equilibrium thermodynamic observables, normalized according to the number of gluons, are weakly dependent on N (the `physical case' N = 3 being already very close to the large-N limit), and can be successfully described by holographic gauge/gravity models. The implications of these findings for a potentially realistic stringy description of the QCD plasma, as well as some open problems for future research, will be pointed out.

This talk is based on arXiv:0907.3719 [hep-lat].