Spherically Symmetric Solutions in F(R) Gravity and Gravitational Repulsion

TL;DR

This paper investigates spherically symmetric solutions in F(R) gravity, revealing conditions under which gravity can become repulsive, potentially explaining cosmic void formation and modifying classical stability analyses.

Contribution

It identifies parameter ranges where flat space-time approximation holds and shows that high-amplitude oscillations in curvature can lead to gravitational repulsion in large objects.

Findings

Modified gravity can be repulsive for large astronomical objects.

High-frequency curvature oscillations alter Jeans instability analysis.

Potential explanation for cosmic void formation.

Abstract

Spherically symmetric solutions in F(R) theories in astronomical systems with rising energy density are studied. The range of parameters is established for which the flat space-time approximation for the background metric is valid. For the solutions in which the curvature scalar oscillates with large amplitude and high frequency, found in our previous papers, it is shown that the analysis of the Jeans instability is strongly modified. It is discovered that for large astronomical objects modified gravity can be repulsive, so such objects shrink forming relatively thin shells instead of quasi uniform bodies. This may explain the formation of cosmic voids.