We note that the decoherence of inflationary curvature perturbation ζ is dominated by a boundary term of the gravity action. Although this boundary term cannot affect cosmological correlators 〈ζn〉, it induces much faster decoherence for ζ than that of previous calculations. The gravitational origin of inflationary decoherence sheds light on the quantum (or non-classical) nature of gravity. By comparing with a Schrödinger-Newton toy model of classical gravity, we show that gravity theories of classical or quantum origins can be distinguished by comparing their different impacts on decoherence rate of ζ. Our calculation also indicates that density fluctuation δρ better preserves quantum information than ζ for the purpose of constructing cosmological Bell-like experiments.

In quantum field theory, the in and out states can be related to the full Hamiltonian by the iϵ prescription. A Wick rotation can further bring the correlation functions to Euclidean spacetime where the integrals are better defined. This setup is convenient for analytical calculations. However, for numerical calculations, an infinitesimal ϵ or a Wick rotation of numerical functions are difficult to implement. We propose two new numerical methods to solve this problem, namely an Integral Basis method based on linear regression and a Beta Regulator method based on Cesàro/Riesz summation. Another class of partition-extrapolation methods previously used in electromagnetic engineering is also introduced. We benchmark these methods with existing methods using in-in formalism integrals, indicating advantages of these new methods over the existing methods in computation time and accuracy.