R^2 Dark Matter

TL;DR

This paper discusses an extension of gravity called R^2-gravity, which adds a scalar curvature squared term, introducing a scalar field that could explain dark matter without ghosts or phenomenological issues.

Contribution

It presents a ghost-free, phenomenologically viable four-derivative gravity extension with a scalar degree of freedom potentially accounting for dark matter.

Findings

R^2-gravity introduces a scalar field as dark matter candidate.

The theory remains free of ghosts and is phenomenologically viable.

It does not improve ultraviolet behavior of Einstein gravity.

Abstract

There is a non-trivial four-derivative extension of the gravitational spectrum that is free of ghosts and phenomenologically viable. It is the so called $R^2$-gravity since it is defined by the only addition of a term proportional to the square of the scalar curvature. Just the presence of this term does not improve the ultraviolet behaviour of Einstein gravity but introduces one additional scalar degree of freedom that can account for the dark matter of our Universe.