The paper derives general second-order gradient forms of heat flow, bulk viscosity, and shear viscosity for relativistic fluids in the Eckart frame, and claims finite signal speeds from linearized modes.
Determination of the Shear Viscosity Relaxation Time at Weak and Strong Coupling
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abstract
We investigate the microscopic origin of the relaxation time coefficient in relativistic fluid dynamics. We show that the extraction of the shear viscosity relaxation time via the gradient expansion is ambiguous and in general fails to give the correct result. The correct value for the shear viscosity relaxation time is extracted from the slowest non-hydrodynamic pole of the corresponding retarded Green's function, if such a pole is purely imaginary. According to the AdS/CFT correspondence, in strongly-coupled $\mathcal{N}=4$ SYM the non-hydrodynamic poles of the shear stress tensor nearest to the origin have a nonzero real part, which implies that the transient fluid-dynamical equations for this gauge theory are not equivalent to the well-known Israel-Stewart equations.
fields
gr-qc 1years
2019 1verdicts
REJECT 1representative citing papers
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Second order causal hydrodynamics in Eckart frame: using gradient expansion scheme
The paper derives general second-order gradient forms of heat flow, bulk viscosity, and shear viscosity for relativistic fluids in the Eckart frame, and claims finite signal speeds from linearized modes.