| DATE: |
2006-08-21 16:00 - 17:00 |
| PLACE: |
Kenkyu Honkan Rm. 321 |
| TITLE: |
Shear viscosity of pionic gas in ChPT |
| CONTACT: |
tsuda |
| SPEAKER: |
Eiji Nakano (National Taiwan Universit) |
| LANGUAGE: |
English |
| ABSTRACT: |
Using chiral perturbation theory we investigate the QCD\ shear viscosity ($\eta$) to entropy density ($s$) ratio below the deconfinement temperature ($\sim 170$ MeV) with zero baryon number density. It is found that $\eta/s$ of QCD is monotonically decreasing in temperature ($T$) and reaches $0.6$ with estimated $\sim 50\%$ uncertainty at $T=120$ MeV. A naive extrapolation of the leading order result shows that $\eta/s$ reaches the $1/4\pi$ minimum bound proposed by Kovtun, Son, and Starinets using string theory methods at $T\sim 200$ MeV. This suggests a phase transition or cross over might occur at $T\lesssim 200$ MeV in order for the bound to remain valid. Also, it is natural for $\eta/s$ to stay close to the minimum bound around the phase transition temperature as was recently found in heavy ion collisions. |
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