Dobado González, AntonioLlanes Estrada, Felipe JoséTorres Rincón, Juan Miguel2023-06-202023-06-202011-08-030370-269310.1016/j.physletb.2011.06.059https://hdl.handle.net/20.500.14352/43704© 2011 Elsevier B.V. Work supported by grants FPA 2008-00592, FIS2008-01323, FPA2007-29115-E, PR34-1856-BSCH, UCM-BSCH GR58/08 910309, PR34/07-15875 (Spain). J.M.T.-R. is a recipient of an FPU scholarship.We study the bulk viscosity of a pion gas in unitarized Chiral Perturbation Theory at low and moderate temperatures, below any phase transition to a quark-gluon plasma phase. We argue that inelastic processes are irrelevant and exponentially suppressed at low temperatures. Since the system falls out of chemical equilibrium upon expansion, a pion chemical potential must be introduced, so we extend the existing theories that include it. We control the zero modes of the collision operator and Landau's conditions of fit when solving the Boltzmann equation with the elastic collision kernel. The dependence of the bulk viscosity with temperature is reminiscent of the findings of Fernández-Fraile and Gómez Nicola (2009) [1], while the numerical value is closer to that of Davesne (1996) [2]. In the zero-temperature limit we correctly recover the vanishing viscosity associated to a non-relativistic monoatomic gas.engjournal articlehttp://www.sciencedirect.com/science/article/pii/S0370269311007143 y http://arxiv.org/abs/1103.0735http://www.sciencedirect.comhttp://arxiv.org/abs/1103.0735open access53Bulk ViscosityPion GasInverse Amplitude MethodHeavy Ion CollisionsElastic Pion ScatteringFísica (Física)22 Física