Initial state entanglement in inflationary cosmology (Vol. 47 No. 1)

Recent observational data indicate that inflationary cosmology gives an excellent description of the very early universe. Inflationary cosmology assumes that quantum fluctuations seed the observed large scale structure in the universe. So we may be able to test the initial quantum state of the universe observationally in the future. Especially, if primordial vacuum state is entangled, the effect of entanglement could then be observed.

We give a new interpretation of the effect of initial state entanglement on the spectrum of vacuum fluctuations. We consider an initially entangled state between two free massive scalar fields in de Sitter space. We construct the initial state by making use of a Bogoliubov transformation between the Bunch-Davies vacuum and a four-mode squeezed state, and then derive the exact power spectrum for one of the scalar fields. We demonstrate that an oscillatory spectrum hardly appears for the initially entangled state unless an ad hoc absolute value of the Bogoliubov coefficients is chosen. We stress that, on the contrary, an initially non-entangled state may naturally produce an oscillatory spectrum due to quantum interference if the initial state deviates from the Bunch-Davies vacuum.

S. Kanno, A note on initial state entanglement in inflationary cosmology, EPL 111, 60007 (2015)
[Abstract]