Decoherence of Cosmological Perturbations from Boundary Terms and the Non-Classicality of Gravity

TL;DR

This paper demonstrates that boundary terms in gravity actions significantly influence the decoherence of inflationary perturbations, providing insights into the quantum nature of gravity and implications for cosmological quantum experiments.

Contribution

It reveals the dominant role of boundary terms in inflationary decoherence and distinguishes classical from quantum gravity effects through decoherence rates.

Findings

Boundary terms cause faster decoherence of curvature perturbations.

Decoherence rates differ between classical and quantum gravity models.

Density fluctuations better preserve quantum information than curvature perturbations.

Abstract

We note that the decoherence of inflationary curvature perturbation $\zeta$ is dominated by a boundary term of the gravity action. Although this boundary term cannot affect cosmological correlators $\left\langle \zeta^n \right\rangle$, it induces much faster decoherence for $\zeta$ 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 Schr\"odinger-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 $\zeta$. Our calculation also indicates that density fluctuation $\delta\rho$ better preserves quantum information than $\zeta$ for the purpose of constructing cosmological Bell-like experiments.