Entanglement Entropy and Decoupling in the Universe

Understand

In the expanding universe, two interacting fields are no longer in thermal contact when the interaction rate becomes smaller than the Hubble expansion rate.

• After decoupling, two subsystems are usually treated separately in accordance with equilibrium thermodynamics and the thermodynamic entropy gives a fiducial quantity conserved in each subsystem.
• In this paper, we discuss a correction to this paradigm from quantum entanglement of two coupled fields.
• The thermodynamic entropy is generalized to the entanglement entropy.