Cosmological constant problem and long-distance modifications of Einstein theory

TL;DR

This paper develops a covariant nonlocal action for modified gravity theories aimed at addressing the cosmological constant problem and cosmic acceleration, highlighting the role of curvature-squared terms in the Einstein-Hilbert action.

Contribution

It introduces a covariant nonlocal formulation of gravity modifications motivated by cosmological issues, emphasizing the structure of the Einstein-Hilbert action in curvature expansion.

Findings

Constructed a covariant nonlocal action for modified gravity.

Revealed the curvature-squared terms in the covariant curvature expansion.

Provided insights into long-distance modifications of Einstein's theory.

Abstract

We construct the covariant nonlocal action for recently suggested long-distance modifications of gravity theory motivated by the cosmological constant and cosmological acceleration problems. This construction is based on the special nonlocal form of the Einstein-Hilbert action explicitly revealing the fact that this action within the covariant curvature expansion begins with curvature-squared terms.