Quantum cosmology, eternal inflation, and swampland conjectures

Abstract

In light of the recent swampland conjectures, we explore quantum cosmology and eternal inflation beyond the slow roll regime. We consider a model of a closed universe with a scalar field $\varphi$ in the framework of tunneling approach to quantum cosmology. The scalar field potential is assumed to have a maximum at $\varphi =0$ and can be approximated in its vicinity as $V(\varphi )\approx 3H^2-\frac{1}{2}{m}^2{\varphi }^2$. Using the instanton method, we find that for $m<2H$ the dominant nucleation channel for the universe is tunneling to a homogeneous, spherical de Sitter space. For larger values of $m/H$, the most probable tunneling is to an inhomogeneous closed universe with a domain wall wrapped around its equator. We determine the quantum state of the field $\varphi$ in the nucleated universe by solving the Wheeler-DeWitt equation with tunneling boundary conditions. Our results agree with earlier work which assumed a slow-roll regime $m\ll H$. We finally show that spherical universes nucleating with $m<2H$ undergo stochastic eternal inflation with inflating regions forming a fractal of dimension $d>2$. For larger values of $m$ the field $\varphi$ is unstable with respect to formation of domain walls and cannot be described by a perturbative stochastic approach.

28 pages, 9 figures