Electromagnetic fields and transport coefficients in a hot pion gas

We present recent results on finite temperature electromagnetic form factors and the electrical conductivity in a pion gas. The standard Chiral Perturbation Theory power counting needs to be modified for transport coefficients. We pay special attention to unitarity and to possible applications for dilepton and photon production.Comment: 4pp, 2 figures, talk given at "Strong and Electroweak Matter 2006", BNL, May 200

Topological thermalization via vortex formation in ultra-fast quenches

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Chiral symmetry and mesons in hot and dense matter: recent developments

We review recent results on properties of the meson gas relevant for Heavy Ion Collision and Nuclear Matter experiments, within the framework of chiral lagrangians. In particular, we describe the temperature and density evolution of the $\sigma$ and $\rho$ poles and its connection with chiral symmetry restoration, as well as the chemical nonequilibrated phase and transport coefficients.Comment: Proceedings of the "Chiral10 International Workshop on Chiral Symmetry in Hadrons and Nuclei", Valencia, Spain, 21-24 june 2010. 9 pages, 5 figures. AIP Proceedings styl

Transport coefficients of a massive pion gas

We review or main results concerning the transport coefficients of a light meson gas, in particular we focus on the case of a massive pion gas. Leading order results according to the chiral power-counting are presented for the DC electrical conductivity, thermal conductivity, shear viscosity, and bulk viscosity. We also comment on the possible correlation between the bulk viscosity and the trace anomaly in QCD, as well as the relation between unitarity and a minimum of the quotient $\eta/s$ near the phase transition.Comment: Talk given at the 5th International Conference on Quarks and Nuclear Physics (QNP09), Beijing, September 21-26, 200

Pion scattering poles and chiral symmetry restoration

Using unitarized Chiral Perturbation Theory methods, we perform a detailed analysis of the $\pi\pi$ scattering poles $f_0(600)$ and $\rho(770)$ behaviour when medium effects such as temperature or density drive the system towards Chiral Symmetry Restoration. In the analysis of real poles below threshold, we show that it is crucial to extend properly the unitarized amplitudes so that they match the perturbative Adler zeros. Our results do not show threshold enhancement effects at finite temperature in the $f_0(600)$ channel, which remains as a pole of broad nature. We also implement T=0 finite density effects related to chiral symmetry restoration, by varying the pole position with the pion decay constant. Although this approach takes into account only a limited class of contributions, we reproduce the expected finite density restoration behaviour, which drives the poles towards the real axis, producing threshold enhancement and $\pi\pi$ bound states. We compare our results with several model approaches and discuss the experimental consequences, both in Relativistic Heavy Ion Collisions and in $\pi\to \pi\pi$ and $\gamma\to \pi\pi$ reactions in nuclei.Comment: 17 pages, 9 figures, final version to appear in Phys.Rev.D, added comments and reference

Bulk viscosity and the conformal anomaly in the pion gas

We calculate the bulk viscosity of the massive pion gas within Unitarized Chiral Perturbation Theory. We obtain a low temperature peak arising from explicit conformal breaking due to the pion mass and another peak near the critical temperature, dominated by the conformal anomaly through gluon condensate terms. The correlation between bulk viscosity and conformal breaking supports a recent QCD proposal. We discuss the role of resonances, heavier states and large-$N_c$ counting.Comment: Revised version accepted in Phys.Rev.Lett. 4 pages, 3 figure

Transport coefficients in Chiral Perturbation Theory

We present recent results on the calculation of transport coefficients for a pion gas at zero chemical potential in Chiral Perturbation Theory using Linear Response Theory. 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 nonzero shear viscosity. In addition, our values for the shear viscosity to entropy ratio satisfy the KSS bound.Comment: 3 pages, 6 figures, EPJA style. Talk given at the QNP06 conference in Madrid, and accepted for publication in EPJ