TY - JOUR
T1 - Dark-energy dynamics required to solve the cosmic coincidence
AU - Egan, Chas A.
AU - Lineweaver, Charles H.
PY - 2008/10/20
Y1 - 2008/10/20
N2 - Dynamic dark-energy (DDE) models are often designed to solve the cosmic coincidence (why, just now, is the dark-energy density ρde the same order of magnitude as the matter density ρm?) by guaranteeing ρde∼ρm 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 ρde∼ρm. Precisely when, and for how long, must a DDE model have ρde∼ρm 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=w0+wa(1-a) over a few e-folds has ρde∼ρm 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 ρde∼ρm.
AB - Dynamic dark-energy (DDE) models are often designed to solve the cosmic coincidence (why, just now, is the dark-energy density ρde the same order of magnitude as the matter density ρm?) by guaranteeing ρde∼ρm 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 ρde∼ρm. Precisely when, and for how long, must a DDE model have ρde∼ρm 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=w0+wa(1-a) over a few e-folds has ρde∼ρm 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 ρde∼ρm.
UR - http://www.scopus.com/inward/record.url?scp=55649111596&partnerID=8YFLogxK
U2 - 10.1103/PhysRevD.78.083528
DO - 10.1103/PhysRevD.78.083528
M3 - Article
SN - 1550-7998
VL - 78
JO - Physical Review D - Particles, Fields, Gravitation and Cosmology
JF - Physical Review D - Particles, Fields, Gravitation and Cosmology
IS - 8
M1 - 083528
ER -