Robustness of the Cosmological Constant Damping Mechanism Through Matter Eras

TL;DR

This paper investigates a scalar-tensor gravity model that naturally maintains a small Hubble rate across different cosmic eras, aligning with observations and addressing the cosmological constant problem.

Contribution

It demonstrates a parameter space region where the model reproduces standard cosmological evolution and satisfies observational constraints, enhancing the viability of the damping mechanism.

Findings

Model reproduces standard cosmological evolution through radiation and matter eras.

Automatically satisfies constraints on fifth force interactions.

Maintains a small Hubble rate regardless of initial vacuum energy.

Abstract

A dynamical resolution to the cosmological constant fine-tuning problem has been previously put forward, based on a scalar-tensor gravitational theory possessing de Sitter attractor solutions characterized by a small Hubble expansion rate, irrespective of an initially large vacuum energy. We show that a technically natural subregion of the parameter space yields a cosmological evolution through radiation- and matter-dominated eras that is essentially indistinguishable from that predicted by General Relativity. Similarly, the proposed model automatically satisfies the observational constraints on a fifth force mediated by the new scalar degree of freedom.