Gravitational Origin of Phantom Dark Energy and Late Cosmic Acceleration

TL;DR

This paper proposes a novel approach to dark energy using the Ricci scalar's dual role, leading to a modified Friedmann equation that explains late cosmic acceleration and addresses the big-rip problem.

Contribution

It introduces a new dark energy model based on Ricci scalar dual roles, resulting in a brane-inspired Friedmann equation without extra dimensions.

Findings

Acceleration can be transient or encounter big-rip depending on cosmic tension sign.

Dark energy behavior as barotropic fluid and Chaplygin gas can prevent big-rip.

Transition time from deceleration to acceleration is derived as a function of equation of state.

Abstract

In this letter, dark energy is obtained using dual roles of the Ricci scalar (as a physical field as well as geometry). Dark energy density, obtained here, mimics phantom and the derived Friedmann equation contains a term $\rho^2_{\rm de}/2 \lambda$ with $\rho_{\rm de}$ being the dark energy density and $\lambda$ being the cosmic tension. It is like brane-gravity inspired Friedmann equation, which arises without using the brane-gravity theory. It is found that acceleration is transient for $\lambda < 0$, but for $\lambda > 0$, expansion is found to encounter big-rip problem. It is shown that this problem can be avoided if dark energy behaves as barotropic fluid and generalized Chaplygin gas simultaneously. Moreover, time for transition (from deceleration to acceleration of the universe) is derived as a function of equation of state parameter ${\rm w}_{\rm de} = p_[rm de}/\rho_{\rm de}$ with $p_{\rm de}$ being the pressure for dark energy fluid..