The Unruh Effect in Relativistic Fluids

TL;DR

This paper explores the relativistic-fluid analogue of the Unruh effect, showing that a comoving probe detects a Thermodynamic Unruh temperature, which is frame-independent and universal across various out-of-equilibrium fluid theories.

Contribution

It introduces a novel relativistic-fluid framework for the Unruh effect, linking frame changes to a Thermodynamic Boost and defining a Thermodynamic Acceleration.

Findings

Thermodynamic Unruh temperature is frame-independent.

The effect is universal across different relativistic fluid models.

Frame changes can be described as local hyperbolic rotations in state space.

Abstract

We identify the relativistic-fluid counterpart of the Unruh effect, in which a comoving probe measures a Thermodynamic Unruh temperature. Frame changes in first-order hydrodynamics are recast as a local, time-dependent hyperbolic rotation in a Rindler-style state space where the instantaneous map between frames is the Thermodynamic Boost and its proper-time variation defines the Thermodynamic Acceleration, which results in an Unruh-like thermal spectrum. To leading order, the Thermodynamic Unruh temperature is frame-independent and universal across out-of-equilibrium relativistic fluid descriptions, from Israel-Stewart to modern theories.