Energy Density Bounds in Cubic Quasi-Topological Cosmology

TL;DR

This paper explores the thermodynamical and causal properties of cubic Quasi-Topological Gravity models in four dimensions, revealing new early-time acceleration phases and deriving density bounds for consistent cosmological evolution.

Contribution

It introduces a detailed analysis of cubic Quasi-Topological Gravity in cosmology, highlighting new early acceleration and thermodynamical constraints not previously studied.

Findings

Identifies bounds on matter densities for thermodynamic consistency.

Discovers a new early-time acceleration phase in QTG cosmology.

Calculates QTG corrections to causal diamond volume.

Abstract

We investigate the thermodynamical and causal consistency of cosmological models of the cubic Quasi-Topological Gravity (QTG) in four dimensions, as well as their phenomenological consequences. Specific restrictions on the maximal values of the matter densities are derived by requiring the apparent horizon's entropy to be a non-negative, non-decreasing function of time. The QTG counterpart of the Einstein-Hilbert (EH) gravity model of linear equation of state is studied in detail. An important feature of this particular QTG cosmological model is the new early-time acceleration period of the evolution of the Universe, together with the standard late-time acceleration present in the original EH model. The QTG correction to the causal diamond's volume is also calculated.