Noether constants for the acoustic field in the Robertson-Walker space-time

摘要

The acoustic space-time for sound waves in the isotropic and homogeneous universe inherits the background Robertson-Walker isometries. Noether constants associated with the six-parameter isometry group of this space defines components of the momentum, hyperbolic momentum and angular momentum of sound. These constants are exact and can replace the approximate constants of motion which are currently in use.