Entanglement Viscosity: from Unitarity to Irreversibility in Accelerated Frames

TL;DR

This paper links quantum unitarity and thermodynamic irreversibility via entanglement viscosities in accelerated frames, revealing new connections between acceleration, anomalies, and viscosity bounds in quantum field theories.

Contribution

It introduces the concept of entanglement viscosities in accelerated frames and derives universal formulas relating them to conformal anomalies and viscosity bounds.

Findings

Derived explicit formulas for entanglement shear and bulk viscosities.

Established the relationship between acceleration-induced viscosity and conformal anomalies.

Showed that conformal field theories saturate the viscosity bound in this context.

Abstract

We demonstrate that the unitarity of quantum field theory, through the positivity of spectral functions, underlies thermodynamic irreversibility for a subsystem separated by a horizon, in direct analogy with the irreversibility of renormalization-group flows. To this end, we explicitly find the shear and bulk viscosities -- the entanglement viscosities -- for thermal radiation in Rindler space using the universal spectral representation. A direct consequence of the obtained general formulas is the relationship between the acceleration-induced shear viscosity in flat space and the conformal quantum anomaly in curved space, pointing to a possible novel probe of the conformal anomaly in systems with extreme acceleration. Moreover, for conformal field theories, we explicitly show that globally entanglement viscosity saturates the Kovtun-Son-Starinets bound.