Horizon-free universe

We have studied a theory of gravity, consistent with all astronomical observations, which is an extension of general relativity generated by a gravitational field Lagrangian proportional to $R+A{R}^2$ (where $R$ is the scalar curvature and $A$ is a new dimensional constant). We find cosmological solutions without a particle horizon for any value of $A$, compatible with cosmological observations if $A$ is negative and small enough. It is pointed out that while alleviating the problem of the large-scale physical uniformity of the universe, the theory may also alleviate the problem of the development of smaller-scale structures from an initially isotropic state, and possibly the problem of "hidden mass."