Speaker
Description
By constructing a formal solution to the moment equations of the Boltzmann equation within the relaxation time approximation, we identify the key step that allows relativistic hydrodynamics to capture non-gradient corrections: the elevation of anisotropies to independent dynamical fields with their own evolution equations. This highlights a conceptual distinction between the gradient expansion and relativistic hydrodynamics. While the gradient expansion is valid only in the vicin-
ity of local thermal equilibrium, the introduction of dynamical anisotropies inadvertently capture “non-hydrodynamic” corrections, as their evolution equations can closely approximate the exact dynamical equations by rescaling the transport coefficients. Therefore, relativistic hydrodynamics emerges as more than just a near-equilibrium theory.
