Carrollian Origins of Bjorken Flow

Abstract

Bjorken flow is among the simplest models of fluids moving near the speed of light ($c$) while Carroll symmetry arises as a contraction of Poincaré group when $c\to 0$. We show that Bjorken flow and its phenomenological approximations are completely captured by Carrollian fluids. Carrollian symmetries arise on generic null surfaces and a fluid moving at $c$ is restricted to such a surface, thereby naturally inheriting the symmetries. Carrollian hydrodynamics is thus not exotic, but rather ubiquitous, and provides a concrete framework for fluids moving at or near the speed of light.

Comments: 7 pages, 2 figures. v2: Minor presentation changes. Matches version published in PRL