Viscosities of Hot Gluon : A Lattice QCD Study

We present transport coefficients (shear viscosity, η, and bulk viscosity, ζ) for the gluon system obtained by the lattice QCD. This is an indispensable calculation towards the understanding of "New State of Matter" observed in RHIC. We study the temperature regions of RHIC (1.4 ≤ T / Tc ≤ 1.8) and much higher ones up to T / Tc ~ 20. In RHIC regions, the ratio of shear viscosity to entropy density, η / s, is around ~ 0.1 - 0.4, and satisfies the KSS bound. At high temperature, η becomes two or three oder of magnitude larger. Our calculation has two limitations: (i) the use of the quench approximation, i.e., without quark pair creation-annihilation effects on vacuum, and (ii) the use of an ansatz for the spectral function. The first point has been well studied in calculations of the spectroscopy and the phase-transition behavior. To investigate the second point, we compare our results with perturbative calculations in high T-regions, and also check the effects of the modification of the spectral function on the viscosity