Halting eternal acceleration with an effective negative cosmological constant

TL;DR

This paper investigates a cosmological model with a negative cosmological constant and a scalar field, demonstrating it can fit observational data and potentially halt eternal acceleration, and reconstructs an equivalent f(R) gravity theory.

Contribution

It introduces a model with negative b3 and a scalar field that fits observational data and reconstructs an equivalent f(R) gravity theory to avoid theoretical issues.

Findings

The model fits supernova, galaxy cluster, and CMB data well.

A negative b3 can halt eternal acceleration.

An equivalent f(R) theory reproduces the same dynamics.

Abstract

In order to solve the problem of eternal acceleration, a model has been recently proposed including both a negative cosmological constant $\Lambda$ and a scalar field evolving under the action of an exponential potential. We further explore this model by contrasting it against the Hubble diagram of Type Ia supernovae, the gas mass fraction in galaxy clusters and the acoustic peak and shift parameters. It turns out that the model is able to fit quite well this large dataset so that we conclude that a negative $\Lambda$ is indeed allowed and could represent a viable mechanism to halt eternal acceleration. In order to avoid problems with theoretical motivations for both a negative $\Lambda$ term and the scalar field, we reconstruct the gravity Lagrangian $f(R)$ of a fourth order theory of gravity predicting the same dynamics (scale factor and Hubble parameter) as the starting model. We thus end up with a $f(R)$ theory able to both fit the data and solve the problem of eternal acceleration without the need of unusual negative $\Lambda$ and ad hoc scalar fields.