Instabilities in tensorial nonlocal gravity

TL;DR

This paper examines nonlocal tensorial modifications to general relativity and finds that, in most cases, these models lead to unstable cosmological evolutions due to rapidly growing energy densities.

Contribution

It provides a detailed analysis of the stability issues in tensorial nonlocal gravity models within cosmology, highlighting their general instability.

Findings

Nonlocal tensorial gravity models often cause rapidly increasing energy densities.

Most models do not support stable cosmological evolution.

Stable solutions are only found in very particular cases.

Abstract

We discuss the cosmological implications of nonlocal modifications of general relativity containing tensorial structures. Assuming the presence of standard radiation- and matter-dominated eras, we show that, except in very particular cases, the nonlocal terms contribute a rapidly growing energy density. These models therefore generically do not have a stable cosmological evolution.