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Register a new user$eta(T)/s (T)$ and collective flow in chiral hydrodynamics
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Using relativistic conformal hydrodynamics coupled to the linear $sigma$ model we study the evolution of matter created in heavy--ion collisions. We focus the study on the influence of the dynamics of the chiral fields on the charged-hadron elliptic flow $v_2$ for a temperature--independent as well as for a temperature--dependent $eta/s$ that is calculated from kinetic theory. We find that $v_2$ is not very sensitive to the coupling of chiral fields to the hydrodynamic evolution, but the temperature dependence of $eta/s$ plays a much bigger role on this observable.
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The relation between the specific shear viscosity $eta/s$ and the dimensionless jet quenching parameter $hat{q}/T^3$ in perturbative QCD is explored at next-to-leading order in the coupling constant. It is shown that the relation changes little, although both transport coefficients independently are subject to large modifications at the NLO level. This finding confirms that the relationship is robust.
Recently, Higgsless models have proven to be viable alternatives to the Standard Model (SM) and supersymmetric models in describing the breaking of the electroweak symmetry. Whether extra-dimensional in nature or their deconstructed counterparts, the physical spectrum of these models typically consists of ``towers of massive vector gauge bosons which carry the same quantum numbers as the SM W and Z. In this paper, we calculate the one-loop, chiral-logarithmic corrections to the S and T parameters from the lightest (i.e. SM) and the next-to-lightest gauge bosons using a novel application of the Pinch Technique. We perform our calculation using generic Feynman rules with generic couplings such that our results can be applied to various models. To demonstrate how to use our results, we calculate the leading chiral-logarithmic corrections to the S and T parameters in the deconstructed three site Higgsless model. As we point out, however, our results are not exclusive to Higgsless models and may, in fact, be used to calculate the one-loop corrections from additional gauge bosons in models with fundamental (or composite) Higgs bosons.
Various decays of eta and eta-prime are investigated within the framework of U(3) chiral effective field theory in combination with a relativistic coupled-channels approach. Final state interactions are included by deriving s- and p-wave interaction kernels for meson-meson scattering from the chiral effective Lagrangian and iterating them in a Bethe-Salpeter equation. Very good agreement with experimental data is achieved.
The decays eta, eta-prime --> pi+ pi- l+ l- (with l = e, mu) are investigated within a chiral unitary approach which combines the chiral effective Lagrangian with a coupled-channels Bethe-Salpeter equation. Predictions for the decay widths and spectra are given.
Using second--order dissipative hydrodynamics coupled self-consistently to the linear $sigma$ model we study the 2+1 dimensional evolution of the fireball created in Au+Au relativistic collisions. We analyze the influence of the dynamics of the chiral fields on the charged-hadron elliptic flow $v_2$ and on the ratio $v_4/(v_2)^2$ for a temperature-independent as well as for a temperature-dependent viscosity-to-entropy ratio $eta/s$ calculated from the linearized Boltzmann equation in the relaxation time approximation. We find that $v_2$ is not very sensitive to the coupling of chiral sources to the hydrodynamic evolution, but the temperature dependence of $eta/s$ plays a much bigger role on this observable. On the other hand, the ratio $v_4/(v_2)^2$ turns out to be much more sensitive than $v_2$ to both the coupling of the chiral sources and the temperature dependence of $eta/s$.
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