Classicality and Quantum Break-Time for Cosmic Axions

Understand

We investigate the length of the period of validity of a classical description for the cosmic axion field.

• To this end, we first show that we can understand the oscillating axion solution as expectation value over an underlying coherent quantum state.
• Once we include self-interaction of the axion, the quantum state evolves so that the expectation value over it starts to deviate from the classical solution.
• The time-scale of this process defines the quantum break-time.