Fernández Fraile, DanielGómez Nicola, Ángel2023-06-202023-06-202007-031434-600110.1140/epja/i2006-10194-5https://hdl.handle.net/20.500.14352/51390© Società Italiana di Fisica. Conferencia: Hot Quarks Conference 2008 (2008. Aspen, Colorado). We are grateful to A. Dobado and F. Llanes-Estrada for their useful comments. We also acknowledge financial support from the Spanish research projects FPA2004-02602, PR27/05-13955-BSCH, FPA2005-02327 and FPI fellowship BES-2005-6726.We present recent results on the calculation of transport coefficients for a pion gas at zero chemical potential in Chiral Perturbation Theory (ChPT) using the Linear Response Theory (LRT). More precisely, we show the behavior of DC conductivity and shear viscosity at low temperatures. To compute transport coefficients, the standard power counting of ChPT has to be modified. The effects derived from imposing unitarity are also analyzed. As physical applications in relativistic heavy-ion collisions, we show the relation of the DC conductivity to soft-photon production and phenomenological effects related to a non-zero shear viscosity. In addition, our values for the shear viscosity to entropy ratio satisfy the KSS bound.spajournal articlehttp://dx.doi.org/10.1140/epja/i2006-10194-5http://link.springer.comhttp://arxiv.org/abs/hep-ph/0610197open access51-73MatterFísica-Modelos matemáticosFísica matemática