Dark Energy Dominance and Cosmic Acceleration in First Order Formalism

TL;DR

This paper explores a first order Palatini formalism for modified gravity coupled with a scalar field, demonstrating its potential to produce cosmic acceleration, dark energy dominance, and solutions to the cosmological constant problem.

Contribution

It introduces a specific non-linear gravity-scalar system in the Palatini formalism, showing its cosmological implications differ from the metric approach and can address key cosmological issues.

Findings

FRW cosmology can exhibit quintessence or phantom phases.

Gravity-assisted dark energy dominance is confirmed in this formalism.

A dynamical solution to the cosmological constant problem is proposed.

Abstract

The current accelerated universe could be produced by modified gravitational dynamics as it can be seen in particular in its Palatini formulation. We analyze here a specific non-linear gravity-scalar system in the first order Palatini formalism which leads to a FRW cosmology different from the purely metric one. It is shown that the emerging FRW cosmology may lead either to an effective quintessence phase (cosmic speed-up) or to an effective phantom phase. Moreover, the already known gravity assisted dark energy dominance occurs also in the first order formalism. Finally, it is shown that a dynamical theory able to resolve the cosmological constant problem exists also in this formalism, in close parallel with the standard metric formulation.