Anthropic versus cosmological solutions to the coincidence problem

TL;DR

This paper explores cosmological and anthropic solutions to the coincidence problem in dark energy models, showing how universe lifetime and anthropic constraints influence model viability and the coincidence issue.

Contribution

It demonstrates how anthropic constraints can resolve the coincidence problem without requiring dynamical dark energy, and links universe lifetime to model exclusion.

Findings

Models close to ΛCDM are excluded without anthropic constraints.

Stringent anthropic constraints can solve the coincidence problem.

Universe lifetime influences the viability of dark energy models.

Abstract

In this paper we investigate possible solutions to the coincidence problem in flat phantom dark energy models with a constant dark energy equation of state and quintessence models with a linear scalar field potential. These models are representative of a broader class of cosmological scenarios in which the universe has a finite lifetime. We show that, in the absence of anthropic constraints, including a prior probability for the models inversely proportional to the total lifetime of the universe excludes models very close to the $\Lambda {\rm CDM}$ model. This relates a cosmological solution to the coincidence problem with a dynamical dark energy component having an equation of state parameter not too close to -1 at the present time. We further show, that anthropic constraints, if they are sufficiently stringent, may solve the coincidence problem without the need for dynamical dark energy.