MSC defense by Mads Sørensen

Hydrodynamics and Magnetohydrodynamics as an effective field theory

We review relativistic hydrodynamics and magnetohydrodynamics as effective field theories to a first-order in the most general frame. This allows to study both frames' linear stability and causality by applying constraints on some of the involved transport coefficients. This shows that a set of frames satisfies both stability and causality under certain constraints.

Furthermore, the Eckart and Landau-Lifshitz frame is commented on, and the latter is considered in more details for magnetohydrodynamics. We find the linear system for small perturbations and comment on the linear stability and causality criteria.

This modern perspective gives sensible physics without introducing new degrees of freedom as were done in the Israel-Stewart theory.

The constraints for the general frame give criteria of what frames to choose to ensure sensible relativistic theories. This can lead to a better understanding of dissipative effects and include them in astrophysical settings, where it has been common practice to only consider the ideal cases.

Supervisors: Jay Armas and Troels Harmark
Censor: Marta Orselli