Causality and dissipation in relativistic polarizeable fluids

Understand

We analyze the breakdown of causality for the perfect fluid limit in a medium with polarizeability.

• We show that to restore causality a relaxation term linking vorticity and polarization, analogous to the Israel-Stewart term linking viscous forces and gradients,is required.
• This term provides a minimum amount of dissipation a locally thermalized relativistic medium with polarizeability must have, independently of its underlying degrees of freedom.
• For ferromagnetic materials an infrared acausal mode remains, which we interpret as a Banks-Casher mode signaling spontaneous magnetization.