# Ricci-Gauss-Bonnet holographic dark energy in Chern-Simons modified gravity: A flat FLRW quintessence-dominated universe

## TL;DR

This paper explores Ricci-Gauss-Bonnet holographic dark energy within Chern-Simons modified gravity, analyzing cosmic evolution and pressure behavior, revealing sign flips and singularities that influence the universe's transition from deceleration to acceleration.

## Contribution

It introduces specific solutions in Chern-Simons modified gravity that model holographic dark energy with sign-changing pressure and discusses their implications for cosmic evolution.

## Key findings

- Predicts sign flip in cosmic pressure during transition from deceleration to acceleration
- Shows asymptotic quintessence-dominated universe in the far future
- Identifies pressure and equation of state singularities at specific cosmic times

## Abstract

We discuss the recently suggested Ricci-Gauss-Bonnet holographic dark energy in Chern-Simons modified gravity. We have tested some general forms of the scale factor $a(t)$, and used two physically reasonable forms which have been proved to be consistent with observations. Both solutions predict a sign flipping in the evolution of cosmic pressure which is positive during the early-time deceleration and negative during the late-time acceleration. This sign flipping in the evolution of cosmic pressure helps in explaining the cosmic deceleration-acceleration transition, and it has appeared in other cosmological models in different contexts. However, the current work shows a pressure singularity which needs to be explained. The evolution of the equation of state parameter $\omega(t)$ shows the same asymptotic behavior for both solutions indicating a quintessence-dominated universe in the far future. We also note that $\omega(t)$ goes to negative values (leaving the decelerating dust-dominated era at $\omega=0$) at exactly the same time the pressure becomes negative. Again, there is another singularity in the behavior of $\omega(t)$ which happens at the same cosmic time of the pressure singularity.