Cosmological stealths with nonconformal couplings

TL;DR

This paper investigates the existence of stealth fields in cosmology with nonconformal couplings, showing they can coexist with different matter phases in the universe's evolution, unlike the conformal case.

Contribution

It demonstrates that nonconformal couplings allow homogeneous stealths to coexist with various matter-dominated phases in the universe's evolution.

Findings

Inhomogeneous stealths are only possible in de Sitter backgrounds.

Homogeneous stealths can coexist with all matter phases in the ΛCDM model.

Nonconformal couplings expand the conditions for stealth field existence.

Abstract

In this paper we reconsider the existence of stealth fields during the evolution of our Universe by admitting more realistic nonminimal couplings to gravity than the conformal one. In the framework of the FRW cosmology we found that inhomogeneous stealths, as those enabled in the conformal case, are only allowed in de Sitter backgrounds. In particular, it is shown that the homogeneous stealths resulting from nonconformal couplings can coexist with each kind of matter dominant in the several phases characterizing the evolution of our Universe according to the $\Lambda$CDM model.