Scale invariance and a gravitational model with non-eternal inflation

TL;DR

This paper introduces a gravity model that naturally produces early inflation, standard cosmological epochs, and late-time acceleration without scalar fields, relying on scale invariance and breaking Lorentz invariance in the gravitational sector.

Contribution

It presents a novel 3+1 dimensional gravity model that achieves a unified description of cosmic inflation, matter domination, and late acceleration without scalar fields, incorporating scale invariance and modified Lorentz symmetry.

Findings

Achieves early inflation and late acceleration with large hierarchy of cosmological constants.

Smooth transition from inflation to radiation era without scalar fields.

Resembles Einstein gravity in weak fields despite Lorentz invariance breaking.

Abstract

We propose a 3 + 1 dimensional model of gravity which results in inflation at early times, followed by radiation- and matter-dominated epochs and a subsequent acceleration at late times. Both the inflation and late time acceleration are nearly de Sitter with a large hierarchy between the effective cosmological constants. There is no scalar field agent of inflation, and the transition from the inflation to the radiation-dominated period is smooth. This model is designed so that it yields, at the cost of giving up on Lorentz invariance in the gravitational sector, the Dirac-Born-Infeld type conformal scalar theory when the universe is conformally flat. It, however, resembles Einstein's gravity with the Gibbons-Hawking-York boundary term in weakly curved space-times.