# Bonn 2010 – wissenschaftliches Programm

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# T: Fachverband Teilchenphysik

## T 13: QCD (Theorie) IV / Quantenfeldtheorie II

### T 13.6: Vortrag

### Donnerstag, 18. März 2010, 18:10–18:25, HG XVI

**Gauge/string duality at zero and finite temperature** — •Eugenio Megias, Kambis Veshgini, Jun Nian, Hans-Juergen Pirner, and E.-Michael Ilgenfritz — Institute for Theoretical Physics, University of Heidelberg, Philosophenweg 19, D-69120 Heidelberg, Germany

We explore some of the features of the Polyakov loop, heavy quark free energy and the thermodynamics of the confined and deconfined phases of QCD within the AdS/QCD formalism. Using a consistent treatment based on 5D Einstein-dilaton gravity with a dilaton potential, the computation of the Einstein equations leads to two solutions: the thermal graviton gas solution corresponding to a confined phase, and the black hole solution which is characterized by the existence of an horizon, corresponding to a deconfined phase. The first solution leads to a precise computation of the heavy qq free energy in the confined phase, with a estimation of *T*_{c} in very good agreement with lattice data. The second solution gives also very good results for the expectation value of the Polyakov loop and equation of state, when an ansatz for the breaking of conformal in
variance is taken into account. This ansatz mimics the running of the coupling in QCD. This is a remarkable fact, because this means that the formalism incorporates in a natural way power corrections, and it allows for a perfectly invariant way to introduce condensates of dimension two. We extend this study also to compute the behavior of the shear and bulk viscosities in the gluon plasma, showing a good agreement with recent lattice data.