The Conformal Stealth of any Standard Cosmology

TL;DR

This paper demonstrates that any homogeneous and isotropic universe can host a conformally invariant scalar field that remains invisible to the universe's dynamics, existing without backreaction and extending to higher dimensions.

Contribution

It introduces the concept of conformal stealths in cosmology, showing their universal presence in standard models regardless of topology or matter content, including higher-dimensional cases.

Findings

Existence of conformal stealths in all homogeneous and isotropic universes.

Stealths evolve without affecting the universe's evolution.

Extension of stealth concept to higher-dimensional cosmologies.

Abstract

It is shown that any homogeneous and isotropic universe, independently of its spatial topology and matter content, allows for the presence of a conformal stealth, i.e. a nontrivial conformally invariant scalar field with vanishing energy-momentum tensor, which evolves along with the universe without causing even the smallest backreaction. Surprisingly, this gravitationally invisible universal witness is inhomogeneous with zero consequences for the underlying cosmology. Additionally, it is shown that these results are not exclusive of a four-dimensional universe by generalizing them to higher dimensions.