RT Journal Article T1 Transport coefficients in chiral perturbation theory A1 Fernández Fraile, Daniel A1 Gómez Nicola, Ángel AB 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. PB Springer SN 1434-6001 YR 2007 FD 2007-03 LK https://hdl.handle.net/20.500.14352/51390 UL https://hdl.handle.net/20.500.14352/51390 LA spa NO © 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. NO Spanish research projects NO BSCH NO FPI programme DS Docta Complutense RD 23 abr 2025