The H-theorem for the entropy of waves

• DOI: 10.1016/j.physleta.2021.127315
• Publication Date: 2021-03-23T18:28:30Z
• Authors: Eiichirou Kawamori
• Keywords: 0103 physical sciences; 01 natural sciences

Abstract In a previous study I defined the nonequilibrium entropy of classical waves in terms of the density matrix of the wave amplitude (the square root of the wave action density). In the present work, I derive the H-theorem for this entropy for weak nonlinear waves whose equations of motion are written in a symplectic form. This formulation enables us to define the Helmholtz free energy of waves in classical plasmas.