Transport coefficients for bulk viscous evolution in the relaxation time approximation

Fecha: Martes 23 de Septiembre
Hora: de 12:00h a 13:00h
Lugar: Seminario de Física Atómica, Molecular y Nuclear (tercera planta de física)

Speaker:
Radoslaw Ryblewski  del INP Cracovia (Polonia) y Kent State Universty (EEUU)

Abstract:
We calculate the transport coefficients necessary for the second-order hydrodynamic evolution of the bulk viscous pressure and the shear stress tensor using the iterative Chapman-Enskog method. We demonstrate that the transport coefficients obtained using the Chapman-Enskog method are different than those obtained previously using 14-moment approximation for finite particle mass. Specializing to the case of boost-invariant and transversally homogeneous longitudinal expansion we compute the temporal evolution of the pressure anisotropy and bulk pressure. We show that the transport coefficients obtained using the Chapman-Enskog method result in better agreement with the exact solution of the Boltzmann equation in the relaxation time approximation compared to results obtained in the 14-moment approximation. We also explicitly confirm that within second-order viscous hydrodynamics, the inclusion of the full set of kinetic coefficients, particularly the shear-bulk couplings, is necessary to properly describe the time evolution of the bulk pressure. Finally we compare the results of second-order hydrodynamics with those obtained using the anisotropic hydrodynamics approach. We find that anisotropic  hydrodynamics and second-order viscous hydrodynamics including the shear-bulk couplings are both able to reproduce the exact evolution with comparable accuracy.