de Sitter Space Decay and Cosmological Constant Relaxation in Unimodular Gravity with Charged Membranes

TL;DR

This paper shows that in unimodular gravity with charged membranes, de Sitter space is inherently unstable and decays, leading to a natural explanation for a small cosmological constant without anthropic arguments.

Contribution

It demonstrates the instability of de Sitter space in unimodular gravity with membranes and explains how a tiny cosmological constant naturally emerges in this framework.

Findings

De Sitter space decays in the presence of charged membranes.

The fluxes form a refined discretuum of states.

Almost-Minkowski space is the long-term attractor when flux terms dominate.

Abstract

General covariant unimodular gravity frameworks, based on the Henneaux-Teitelboim formulation, are, in disguise, precisely $4$-form field theories corrected with higher dimension operators. In the presence of charged tensional membranes, any de Sitter space in all such theories is unstable and decays. If the fluxes sourced by membranes are mutually incommensurate, de Sitter geometries comprise a very refined discretuum of states. Whenever the $4$-form sector is dominated by terms linear in flux the almost-Minkowski space is the unique long-time attractor. As a result, a tiny cosmological constant is natural in all such frameworks, without appealing to anthropic reasoning.