BICEP2, non Bunch-Davies and Entanglement

Abstract

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 $r = 0.2$ 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 vacuua are known to lead to pathologies. In this note we propose to interpret them as excited/squeezed states built over the standard Bunch-Davies vacuum and discuss the associated entanglement properties due to de Sitter horizon, and how such an approach may be more natural in the context of inflation.