Initial-state selection in de Sitter cosmology

Determine the physically appropriate initial state for de Sitter cosmology, including whether de Sitter invariance uniquely selects such a state or permits multiple choices.

Background

The paper identifies the specification of an initial state as a major unresolved issue in cosmology. Even when quantum field theory is required to be de Sitter invariant on a fixed background, the discussion emphasizes that this condition may not uniquely determine the state.

The subsequent sections study the Bunch–Davies and Hartle–Hawking wavefunctions as particular constructions, but the broader problem of selecting the physically correct initial state remains unresolved.