Screening fifth forces in k-essence and DBI models

TL;DR

This paper investigates whether non-linear scalar field theories like k-essence and DBI can naturally suppress fifth forces, finding screening mechanisms in some models but not in DBI, with implications for cosmology.

Contribution

It demonstrates the existence of Vainshtein-like screening in k-essence models and shows that DBI models do not exhibit such screening, expanding understanding of scalar field theories.

Findings

Vainshtein-like screening exists in some k-essence models.

DBI models do not support a screening mechanism.

Certain k-essence models can explain cosmic acceleration while suppressing fifth forces.

Abstract

New fifth forces have not yet been detected in the laboratory or in the solar system, hence it is typically difficult to introduce new light scalar fields that would mediate such forces. In recent years it has been shown that a number of non-linear scalar field theories allow for a dynamical mechanism, such as the Vainshtein and chameleon ones, that suppresses the strength of the scalar fifth force in experimental environments. This is known as screening, however it is unclear how common screening is within non-linear scalar field theories. k-essence models are commonly studied examples of non-linear models, with DBI as the best motivated example, and so we ask whether these non-linearities are able to screen a scalar fifth force. We find that a Vainshtein-like screening mechanism exists for such models although with limited applicability. For instance, we cannot find a screening mechanism for DBI models. On the other hand, we construct a large class of k-essence models which lead to the acceleration of the Universe in the recent past for which the fifth force mediated by the scalar can be screened.