BICEP2, non-Bunch–Davies and entanglement

BICEP2 result on the tensor to scalar ratio r   indicates a blue tilt in the primordial gravitational wave spectrum. This blue tilt and the observed large value r=0.2r=0.2 are difficult to accommodate within the single field inflationary scenarios under standard conditions. Non-Bunch–Davies vacuum states have been proposed as a possibility. Such vacua are known to lead to pathologies. In this note we point out that it is known that these states ought to be interpreted as excited/squeezed states built over the standard Bunch–Davies vacuum in order to avoid pathological issues. We discuss the associated entanglement properties due to de Sitter horizon, and how such an approach may be more natural in the context of inflation. In particular, we suggest to employ entanglement considerations in de Sitter background to study the nature and intrinsic properties of modified initial states.