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تسجيل مستخدم جديدTransport coefficients in Chiral Perturbation Theory
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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.
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Chiral perturbation theory is a much successful effective field theory of quantum chromodynamics at low energies. The effective Lagrangian is constructed systematically order by order in powers of the momentum $p^2$, and until now the leading order (
LO), next-to leading order (NLO), next-to-next-to leading order (NNLO) and next-to-next-to-next-to leading order (NNNLO) have been studied. In the following review we consider the construction of the Lagrangian and in particular focus on the NNNLO case. We in addition review and discuss the pion mass and decay constant at the same order, which are fundamental quantities to study for chiral perturbation theory. Due to the large number of terms in the Lagrangian and hence low energy constants arising at NNNLO, some remarks are made about the predictivity of this effective field theory.
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