Screening mechanisms in hybrid metric-Palatini gravity

TL;DR

This paper examines the screening mechanisms in hybrid metric-Palatini gravity, analyzing their effectiveness around astrophysical objects and establishing observational bounds to constrain the model's parameters.

Contribution

It provides a detailed analysis of the thin shell condition in hybrid metric-Palatini gravity and derives observational bounds from solar system experiments.

Findings

Thin shell condition depends on background field value.

Most objects satisfy the thin shell condition, with some exceptions.

Solar system data impose strong constraints on the model.

Abstract

We investigate the efficiency of screening mechanisms in the hybrid metric-Palatini gravity. The value of the field is computed around spherical bodies embedded in a background of constant density. We find a thin shell condition for the field depending on the background field value. In order to quantify how the thin shell effect is relevant, we analyze how it behaves in the neighborhood of different astrophysical objects (planets, moons or stars). We find that the condition is very well satisfied except only for some peculiar objects. Furthermore we establish bounds on the model using data from solar system experiments such as the spectral deviation measured by the Cassini mission and the stability of the Earth-Moon system, which gives the best constraint to date on $f(R)$ theories. These bounds contribute to fix the range of viable hybrid gravity models.