The Cosmological Optical Theorem

Understand

The unitarity of time evolution, or colloquially the conservation of probability, sits at the heart of our descriptions of fundamental interactions via quantum field theory.

• The implications of unitarity for scattering amplitudes are well understood, for example through the optical theorem and cutting rules.
• In contrast, the implications for in-in correlators in curved spacetime and the associated wavefunction of the universe, which are measured by cosmological surveys, are much less transparent.
• For fields of any mass in de Sitter spacetime with general local interactions, which need not be invariant under de Sitter isometries, we show that unitarity implies an infinite set of relations among the coefficients $ \psi_{n} $ of the wavefunction of the universe with $ n $ fields, which we name Cosmological Optical Theorem.