Self-accelerated universe induced by repulsive effects as an alternative to dark energy and modified gravities

TL;DR

This paper proposes a geometrical mechanism for cosmic acceleration based on intrinsic repulsive effects in space-time, unifying dark energy and inflation without introducing new fields or modifying gravity laws.

Contribution

It introduces a novel intrinsic geometrical effect causing repulsive gravity, unifying dark energy and inflation within a single framework based on curvature eigenvalues.

Findings

Repulsive gravity effects naturally emerge in homogeneous and isotropic universes.

The model fits well with recent supernova data.

The approach unifies late-time acceleration and early inflation without extra fields.

Abstract

The existence of current-time universe's acceleration is usually modeled by means of two main strategies. The first makes use of a dark energy barotropic fluid entering \emph{by hand} the energy-momentum tensor of Einstein's theory. The second lies on extending the Hilbert-Einstein action giving rise to the class of extended theories of gravity. In this work, we propose a third approach, derived as an intrinsic geometrical effect of space-time, which provides repulsive regions under certain circumstances. We demonstrate that the effects of repulsive gravity naturally emerge in the field of a homogeneous and isotropic universe. To this end, we use an invariant definition of repulsive gravity based upon the behavior of the curvature eigenvalues. Moreover, we show that repulsive gravity counterbalances the standard gravitational attraction influencing both late and early times of the universe evolution. This phenomenon leads to the present speed up and to the fast expansion due to the inflationary epoch. In so doing, we are able to unify both dark energy and inflation in a single scheme, showing that the universe changes its dynamics when ${\ddot H\over H}=-2\dot H$, at the repulsion onset time where this condition is satisfied. Further, we argue that the spatial scalar curvature can be taken as vanishing because it does not affect at all the emergence of repulsive gravity. We check the goodness of our approach through two cosmological fits involving the most recent union 2.1 supernova compilation.