Thin-wall vacuum decay in the presence of a compact dimension meets the $H_0$ and $S_8$ tensions

Understand

The proposal of a rapid sign-switching cosmological constant in the late universe, mirroring a transition from anti-de Sitter (AdS) to de Sitter (dS) space, has significantly improved the fit to observational data and provides a compelling framework for ameliorating major cosmological tensions, such as the $H_0$ and $S_8$ tensions.

• An attractive theoretical realisation that accommodates the AdS $\to$ dS transition relies on the Casimir forces of fields inhabiting the bulk of a 5-dimensional (5-dim) set up.
• Among the fields characterising the dark sector, there is a real scalar field $\phi$ endowed with a potential holding two local minima with very small difference in vacuum energy and bigger curvature (mass) of the lower one.
• Shortly after the false vacuum tunnels to its true vacuum state, $\phi$ becomes more massive and its contribution to the Casimir energy becomes exponentially suppressed.