Low-curvature quantum corrections from unitary evolution of de Sitter space

TL;DR

This paper investigates the quantum evolution of de Sitter space using unimodular gravity, revealing that unitarity resolves horizon issues and induces strong quantum effects, with minimal impact from loop quantum gravity corrections at low cosmological constants.

Contribution

It demonstrates how unimodular gravity and a natural notion of time lead to a unitary quantum description of de Sitter space, resolving horizon breakdowns and highlighting fundamental conflicts in quantum gravity.

Findings

Unitary evolution resolves de Sitter horizon issues.

Quantum effects become significant at the horizon surface.

Loop quantum gravity corrections are negligible for low cosmological constants.

Abstract

We study the quantum dynamics of de Sitter space formulated as a minisuperspace model with flat spatial hypersurfaces in unimodular gravity, both in the Wheeler-DeWitt approach and in loop quantum cosmology (LQC). Time evolution is defined naturally in unimodular time, which appears as conjugate to the cosmological (integration) constant. We show that requiring unitary time evolution "resolves" the de Sitter horizon where the flat slicing breaks down and leads to strong quantum effects there, even though locally nothing special happens at this surface. For a cosmological constant that is far below the Planck scale, loop quantum gravity corrections do not alter the main results in any substantial way. This model illustrates the fundamental clash between general covariance and unitarity in quantum gravity.