A Graceful Exit for the Cosmological Constant Damping Scenario

TL;DR

This paper introduces a class of scalar-tensor models that dynamically damp the cosmological constant, avoiding large variations in Newton's constant and offering a potential solution to the old cosmological constant problem.

Contribution

It proposes a new scalar-tensor framework that achieves dynamical damping of the cosmological constant without unacceptable variations in Newton's constant.

Findings

Models successfully damp the effective cosmological constant.

Avoids large variations in Newton's constant.

Provides a natural hierarchy of couplings via fermion condensation.

Abstract

We present a broad and simple class of scalar-tensor scenarios that successfully realize dynamical damping of the effective cosmological constant, therefore providing a viable dynamical solution to the fine-tuning or "old" cosmological constant problem. In contrast to early versions of this approach, pioneered in the works of A. Dolgov in the 1980es, these do not suffer from unacceptable variations of Newton's constant, as one aims at a small but strictly positive (rather than zero) late-time curvature. In our approach, the original fine-tuning issue is traded for a hierarchy of couplings, and we further suggest a way to naturally generate this hierarchy based on fermion condensation and softly broken field shift symmetry.