A Unified Universe

TL;DR

This paper proposes a unified gravitational model incorporating local and non-local corrections to explain the universe's evolution from inflation to dark energy-driven acceleration without scalar fields.

Contribution

It introduces a combined local and non-local gravity model that naturally transitions through key cosmic epochs, unifying inflation and dark energy within a single framework.

Findings

The model achieves a graceful exit from inflation via oscillations.

Late-time acceleration is driven by the non-local term.

Both terms are derived from covariant effective field theory.

Abstract

We present a unified evolution of the universe from very early times until the present epoch by including both the leading local correction $R^2$ and the leading non-local term $R\frac{1}{\square^2}R$ to the classical gravitational action. We find that the inflationary phase driven by $R^2$ term gracefully exits in a transitory regime characterized by coherent oscillations of the Hubble parameter. The universe then naturally enters into a radiation dominated epoch followed by a matter dominated era. At sufficiently late times after radiation-matter equality, the non-local term starts to dominate inducing an accelerated expansion of the universe at the present epoch. We further exhibit the fact that both the leading local and non-local terms can be obtained within the covariant effective field theory of gravity. This scenario thus provides a unified picture of inflation and dark energy in a single framework by means of a purely gravitational action without the usual need of a scalar field.