2006/12/20 by Eiji Nakano, Nakano, Eiji
Physics and Astronomy · #FOS: Physical sciences #High Energy Physics - Phenomenology (hep-ph) #High-Energy Particle Collisions Research #Particle physics theoretical and experimental studies #Quantum Chromodynamics and Particle Interactions #hep-ph
paper · pdf · doi:10.48550/arxiv.hep-ph/0612255
13 pages, 4 figures, A contribution to lecture notes for ECT* school on RG and EFT (2006), the draft has already been submitted to editor. Some references were added
openalex publication_date 2006/12/20 · arxiv created 2007/03/21 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
Using chiral perturbation theory we investigate the QCD shear viscosity (η) to entropy density (s) ratio below the deconfinement temperature (∼ 170 MeV) with zero baryon number density. It is found that η/s of QCD is monotonically decreasing in temperature (T) and reaches 0.6 with estimated ∼ 50% uncertainty at T=120 MeV. A naive extrapolation of the leading order result shows that η/s reaches the 1/4π minimum bound proposed by Kovtun, Son, and Starinets using string theory methods at T∼ 210 MeV. This suggests a phase transition or cross over might occur at T\lesssim 210 MeV in order for the bound to remain valid. Also, it is natural for η/s to stay close to the minimum bound around the phase transition temperature as was recently found in heavy ion collisions.