Swampland Constraints on No-Boundary Quantum Cosmology

TL;DR

This paper examines how Swampland conjectures constrain the Hartle-Hawking no-boundary proposal, showing that the likelihood of a classical universe is extremely limited unless certain parameters are very small, which challenges the classical creation scenario.

Contribution

It demonstrates the incompatibility between no-boundary quantum cosmology and Swampland conjectures, providing bounds on parameters for classical universe emergence.

Findings

Classical universe probability is tiny under Swampland constraints.

Parameters must be much smaller than unity for classical solutions to exist.

Order unity parameters lead to the absence of saddle-point solutions, implying a quantum universe.

Abstract

The Hartle-Hawking no-boundary proposal describes the quantum creation of the universe. To have a non-negligible probability to obtain a classical expanding universe, eternal inflation is required, which is severely constrained by Swampland conjectures such as the refined de Sitter conjecture and the distance conjecture. We discuss this issue in detail and demonstrate the incompatibility. We show that the dimensionless parameters in the refined de Sitter conjecture should be bounded from above by a positive power of the scalar potential to realize the classical expanding universe. In other words, the probability of the classical expanding universe is extremely small under the Swampland conjectures unless the parameters are much smaller than unity. If they are order unity, on the other hand, the saddle-point solution itself ceases to exist implying a genuinely quantum universe.