Action Principles for Relativistic Extended Magnetohydrodynamics: A Unified Theory of Magnetofluid Models

Abstract

Two types of Eulerian action principles for relativistic extended magnetohydrodynamics (MHD) are formulated. With the first, the action is extremized under the constraints of density, entropy, and Lagrangian label conservation, which leads to a Clebsch representation for a generalized momentum and a generalized vector potential. The second action arises upon transformation to physical field variables, giving rise to a covariant bracket action principle, i.e., a variational principle in which constrained variations are generated by a degenerate Poisson bracket. Upon taking appropriate limits, the action principles lead to relativistic Hall MHD and well-known relativistic ideal MHD. For the first time, the Hamiltonian formulation of relativistic Hall MHD with electron thermal inertia (akin to [Comisso \textit{et al.}, Phys. Rev. Lett. {\bf 113}, 045001 (2014)] for the electron--positron plasma) is introduced. This thermal inertia effect allows for violation of the frozen-in magnetic flux condition in marked contrast to nonrelativistic Hall MHD that does satisfy the frozen-in condition. We also find violation of the frozen-in condition is accompanied by freezing-in of an alternative flux determined by a generalized vector potential. Finally, we derive a more general 3+1 Poisson bracket for nonrelativistic extended MHD, one that does not assume smallness of the electron ion mass ratio.

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• Gravitational electromotive force in magnetic reconnection around Schwarzschild black holes
• Generalized Magnetofluid Connections in Curved Spacetime
• Helically symmetric extended magnetohydrodynamics: Hamiltonian formulation and equilibrium variational principles
• Direction of cascades in a magnetofluid model with electron skin depth and ion sound Larmor radius scales
• A class of three-dimensional gyroviscous magnetohydrodynamic models
• Generalized general-relativistic magnetohydrodynamic equations for plasmas of active galactic nuclei in the era of the Event Horizon Telescope
• Clebsch representation of relativistic plasma and generalized enstrophy
• Lorentz invariant "potential magnetic field" and magnetic flux conservation in an ideal relativistic plasma
• Yet Another Modification of Relativistic Magnetohydrodynamic Waves: Electron Thermal Inertia
• Revealing Noncanonical Hamiltonian Structures in Relativistic Fluid Dynamics