Dark-Energy Dynamics Required to Solve the Cosmic Coincidence
Loading...
Date
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Description
Dynamic dark energy (DDE) models are often designed to solve the cosmic coincidence (why, just now, is the dark energy density $ρ_{de}$, the same order of magnitude as the matter density $ρ_m$?) by guaranteeing $ρ_{de} \sim ρ_m$ for significant fractions of the age of the universe. This typically entails ad-hoc tracking or oscillatory behaviour in the model. However, such behaviour is neither sufficient nor necessary to solve the coincidence problem. What must be shown is that a significant fraction of observers see $ρ_{de} \sim ρ_m$. Precisely when, and for how long, must a DDE model have $ρ_{de} \sim ρ_{m}$ in order to solve the coincidence? We explore the coincidence problem in dynamic dark energy models using the temporal distribution of terrestrial-planet-bound observers. We find that any dark energy model fitting current observational constraints on $ρ_{de}$ and the equation of state parameters $w_0$ and $w_a$, does have $ρ_{de} \sim ρ_m$ for a large fraction of observers in the universe. This demotivates DDE models specifically designed to solve the coincidence using long or repeated periods of $ρ_{de} \sim ρ_m$.
16 pages, 8 figures, Submitted to Phys. Rev. D
16 pages, 8 figures, Submitted to Phys. Rev. D