Hayashi–Navier–Stokes Formulation: A Unified Description of Higher Angular Modes, Unresolved Degrees of Freedom, and Memory in Kinetic Hydrodynamics
This preprint reformulates the Navier–Stokes viscosity as the effective response that remains after coarse-graining the higher angular modes and unresolved degrees of freedom of the molecular velocity distribution. Using a spherical-harmonic expansion in velocity space and a P/Q projection (P = Pl≤4, Q = I − P), elimin...