Relativistic hydrodynamics from projection operator method

Understand

We study relativistic hydrodynamics in the linear regime, based on Mori's projection operator method.

• In relativistic hydrodynamics, it is considered that ambiguity about the fluid velocity occurs from a choice of a local rest frame: the Landau and Eckart frames.
• We find that the difference of the frames is not the choice of the local rest frame, but rather that of dynamic variables in the linear regime.
• We derive hydrodynamic equations in the both frames by the projection operator method.