Dynamical Aspects of Analogue Gravity: The Backreaction of Quantum Fluctuations in Dilute Bose-Einstein Condensates

TL;DR

This paper investigates how quantum fluctuations influence the classical background in dilute Bose-Einstein condensates, revealing limitations of common semiclassical methods in accurately capturing backreaction effects.

Contribution

It provides an ab initio derivation of backreaction forces in Bose-Einstein condensates and critiques the effectiveness of the effective-action method used in semiclassical quantum gravity.

Findings

Effective-action method fails to fully capture backreaction.

Backreaction derived from microscopic physics shows limitations of semiclassical approaches.

Operator ordering issues affect the calculation of backreaction forces.

Abstract

We discuss the backreaction force exerted by quantum fluctuations in dilute Bose-Einstein condensates onto the motion of the classical background, derived by an ab initio approach from microscopic physics. It is shown that the effective-action method, widely employed in semiclassical quantum gravity, fails to give the full backreaction force. The failure of the effective-action method is traced back, inter alia, to the problem of the correct choice of the fundamental variables and the related operator ordering issues.