Extended relaxation time approximation and relativistic dissipative hydrodynamics

TL;DR

This paper develops an extended relaxation-time approximation for relativistic hydrodynamics derived from the Boltzmann equation, ensuring conservation laws are respected and revealing energy-dependent corrections to transport coefficients.

Contribution

It generalizes the Anderson-Witting approximation to include energy-dependent relaxation times, providing a consistent framework for relativistic dissipative hydrodynamics.

Findings

Transport coefficients receive corrections due to energy dependence.

Derived first-order hydrodynamic equations in the Landau frame.

Reported scaling features of transport coefficient ratios.

Abstract

Development of a new framework for derivation of order-by-order hydrodynamics from Boltzmann equation is necessary as the widely used Anderson-Witting formalism leads to violation of fundamental conservation laws when the relaxation-time depends on particle energy, or in a hydrodynamic frame other than the Landau frame. We generalize an existing framework for consistent derivation of relativistic dissipative hydrodynamics from the Boltzmann equation with a energy-dependent relaxation-time by extending the Anderson-Witting relaxation-time approximation. We argue that the present framework is compatible with conservation laws and derive first-order hydrodynamic equations in landau frame. Further, we show that the transport coefficients, such as shear and bulk viscosity as well as charge and heat diffusion currents, have corrections due to the energy dependence of relaxation time compared to what one obtains from the Anderson-Witting approximation of the collision term. The ratio of these transport coefficients are studied using a parametrized relaxation-time, and several interesting scaling features are reported.