Transient Relativistic Fluid Dynamics in a General Hydrodynamic Frame

TL;DR

This paper introduces a novel second-order relativistic hydrodynamics framework that is frame-independent, includes transient degrees of freedom, and ensures causality and stability, with applications to Bjorken flow.

Contribution

It develops a new frame-independent second-order relativistic hydrodynamics theory with explicit causality and stability conditions, extending existing models.

Findings

Reduces to Bemfica-Disconzi-Noronha-Kovtun theory at first order

Provides causality and stability conditions in the conformal regime

Identifies hydrodynamic variables revealing attractor behavior in Bjorken flow

Abstract

We propose a new theory of second-order viscous relativistic hydrodynamics which does not impose any frame conditions on the choice of the hydrodynamic variables. It differs from Mueller-Israel-Stewart theory by including additional transient degrees of freedom, and its first-order truncation reduces to Bemfica-Disconzi-Noronha-Kovtun theory. Conditions for causality and stability are explicitly given in the conformal regime. As an illustrative example, we consider Bjorken flow solutions to our equations and identify variables which make a hydrodynamic attractor manifest.