In this work, a Bayesian statistical analysis is used to establish probabilistic constraints on the temperature-dependence of bulk viscosity using hadronic measurements from RHIC and LHC. Although its precise magnitude and temperature-dependence in the cross-over region is not fully understood, recent theoretical and phenomenological studies provided evidence that the bulk viscosity can be sufficiently large to have measurable consequences on the evolution of the quark-gluon plasma. While small at very high temperature, the bulk viscosity of Quantum Chromodynamics is expected to grow in the confinement region. Paquet, Jean-FranГѓВ§ois Shen, Chun Denicol, Gabriel Jeon, Sangyong Gale, Charles Phenomenological constraints on the bulk viscosity of QCD

In particular, the configurational term is responsible for the enhancement of the bulk viscosity near the critical point. In all other cases studied, the dilute gas contribution is negligible and the configurational contribution dominates the overall behavior. The dilute gas contribution to the bulk viscosity is seen to be significant only in the cases when intramolecular relaxation times are in the ГЋВјs range, and for low vibrational wave numbers (<1000 cm-1) This explains the abnormally high values of bulk viscosity reported for CO2. Both atomistic and coarse-grained force fields for water, CO2, and n-decane are considered and tested for their accuracy, and where possible, compared to experimental data. As a benchmark, the Lennard-Jones fluid is studied. The configurational part is calculated using Green-Kubo relations for the fluctuations of the pressure tensor obtained from equilibrium microcanonical molecular dynamics simulations. The dilute gas contribution is evaluated using experimental data for the relaxation times of vibrational and rotational degrees of freedom. The bulk viscosity of molecular models of gases and liquids is determined by molecular simulations as a combination of a dilute gas contribution, arising due to the relaxation of internal degrees of freedom, and a configurational contribution, due to the presence of intermolecular interactions. Lastly, this paves the way for an eventual quantitative determination of several QCD transport coefficients from the experimental heavy ion and hadron-nucleus collision programs.

The agreement between a realistic 3D hybrid simulation and the experimentally measured data considerably improves with the addition of a bulk viscosity coefficient for strongly interacting matter. In this study, we investigate the consequences of a nonzero bulk viscosity coefficient on the transverse momentum spectra, azimuthal momentum anisotropy, and multiplicity of charged hadrons produced in heavy ion collisions at LHC energies. Importance of the Bulk Viscosity of QCD in Ultrarelativistic Heavy-Ion Collisions

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