Relaxing the Cosmological Constant: a Proof of Concept

TL;DR

This paper introduces a natural mechanism where a scalar field with a shallow potential dynamically relaxes a large initial cosmological constant to its observed small value, involving NEC violation and leading to standard cosmology.

Contribution

It presents a novel model where NEC violation triggers relaxation of the cosmological constant without eternal inflation, fixing dark energy to a specific value.

Findings

The model achieves a small effective cosmological constant consistent with observations.

It demonstrates a universe evolution from NEC violation to standard Big Bang cosmology.

The approach avoids eternal inflation and fixes dark energy parameters.

Abstract

We propose a technically natural scenario whereby an initially large cosmological constant (c.c.) is relaxed down to the observed value due to the dynamics of a scalar evolving on a very shallow potential. The model crucially relies on a sector that violates the null energy condition (NEC) and gets activated only when the Hubble rate becomes sufficiently small --- of the order of the present one. As a result of NEC violation, this low-energy universe evolves into inflation, followed by reheating and the standard Big Bang cosmology. The symmetries of the theory force the c.c. to be the same before and after the NEC-violating phase, so that a late-time observer sees an effective c.c. of the correct magnitude. Importantly, our model allows neither for eternal inflation nor for a set of possible values of dark energy, the latter fixed by the parameters of the theory.