The gravity lagrangian according to solar system experiments

TL;DR

This paper constrains the form of f(R) gravity theories at low curvatures using solar system experiments, showing that nonlinear modifications are incompatible with observational data and cannot explain cosmic acceleration.

Contribution

It provides bounds on the f(R) function at low curvatures, ruling out certain nonlinear models based on observational constraints.

Findings

Nonlinear f(R) models at low curvature are incompatible with solar system tests.

The f(R) function must be close to linear within specific bounds.

Certain proposed modifications to gravity cannot explain cosmic acceleration without conflicting with observations.

Abstract

In this work we show that the gravity lagrangian f(R) at relatively low curvatures in both metric and Palatini formalisms is a bounded function that can only depart from the linearity within the limits defined by well known functions. We obtain those functions by analysing a set of inequalities that any f(R) theory must satisfy in order to be compatible with laboratory and solar system observational constraints. This result implies that the recently suggested f(R) gravity theories with nonlinear terms that dominate at low curvatures are incompatible with observations and, therefore, cannot represent a valid mechanism to justify the cosmic speed-up.