Dark-energy dynamics required to solve the cosmic coincidence

作者：Egan Chas A^*; Lineweaver Charles H

来源：Physical Review D - Particles, Fields, Gravitation and Cosmology, 2008, 78(8): 083528.

DOI：10.1103/PhysRevD.78.083528

Dynamic dark-energy (DDE) models are often designed to solve the cosmic coincidence (why, just now, is the dark-energy density rho(de) the same order of magnitude as the matter density rho(m)?) by guaranteeing rho(de)similar to rho(m) for significant fractions of the age of the Universe. However, such behavior is neither sufficient nor necessary to solve the coincidence problem. Cosmological processes constrain the epochs during which observers can exist. Therefore, what must be shown is that a significant fraction of observers see rho(de)similar to rho(m). Precisely when, and for how long, must a DDE model have rho(de)similar to rho(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 realistic DDE model which can be parametrized as w=w(0)+w(a)(1-a) over a few e-folds has rho(de)similar to rho(m) for a significant fraction of observers in the Universe. This demotivates DDE models specifically designed to solve the coincidence using long or repeated periods of rho(de)similar to rho(m).

• 出版日期2008-10