Self-acceleration and matter content in bicosmology from Noether Symmetries

TL;DR

This paper explores how Noether symmetries in bigravity cosmologies constrain the behavior of unobservable matter fields, leading to models that either resemble General Relativity or predict a de Sitter universe, with implications for stability.

Contribution

It introduces a method to constrain matter dynamics in bigravity using Noether symmetries, resulting in novel cosmological models with specific phenomenological features.

Findings

Models either decouple to GR or evolve towards de Sitter space.

The conserved quantity from symmetry relates to vacuum energy.

Potential instabilities may favor the GR-like model.

Abstract

In bigravity, when taking into account the potential existence of matter fields minimally coupled to the second gravitation sector, the dynamics of our Universe depends on some matter that cannot be observed in a direct way. In this paper, we assume the existence of a Noether symmetry in bigravity cosmologies in order to constrain the dynamics of that matter. By imposing this assumption we obtain cosmological models with interesting phenomenology. In fact, considering that our universe is filled with standard matter and radiation, we show that the existence of a Noether symmetry implies that either the dynamics of the second sector decouples, being the model equivalent to General Relativity, or the cosmological evolution of our universe tends to a de Sitter state with the vacuum energy in it given by the conserved quantity associated with the symmetry. The physical consequences of the genuine bigravity models obtained are briefly discussed. We also point out that the first model, which is equivalent to General Relativity, may be favored due to the potential appearance of instabilities in the second model.