The success of ideal Relativistic Fluid Dynamics (RFD) in describing hadron spectra and elliptic flow at RHIC has led to a strong interest in the transport coefficients of QCD, in particular the shear- and bulk-viscosity as well as the shear-viscosity over entropy-density ratio η/s. Of course ideal RFD assumes η to be zero, which is unphysical, but its success has hinted at a very small value for η/s. The purpose of this post is to review what we currently know about η/s of QCD matter and put the different approaches used to study this quantity into context.
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…)
This paper deals with the broadening of the near-side distribution of particles at intermediate transverse momentum, associated with a high momentum trigger hadron. (more…)