Many dark energy models fail to pass the cosmic age test because of the old quasar APM 08279+5255 at redshift z=3.91,the ΛCDMmodel and holographic dark energy models being no exception.Inthis paper,we focus onthe topic of the age problem inthe new agegraphic dark energy(NADE)model.We determine the age of the universe in the NADE model by fitting the observational data,including type Ia supernovae(SNIa),baryon acoustic oscillations(BAO)and the cosmic microwave background(CMB).We find that the NADE model also faces the challenge of the age problem caused by the old quasar APM 08279+5255.In order to overcome such a difficulty,we consider the possible interaction between dark energy and dark matter.We show that this quasar can be successfully accommodated in the interacting new agegraphic dark energy(INADE)model at the 2σlevel under the current observational constraints.
We compare some popular dark energy models under the assumption of a flat universe by using the latest observational data including the type Ia supernovae Constitution compilation,the baryon acoustic oscillation measurement from the Sloan Digital Sky Survey,the cosmic microwave background measurement given by the seven-year Wilkinson Microwave Anisotropy Probe observations and the determination of H0 from the Hubble Space Telescope.Model comparison statistics such as the Bayesian and Akaike information criteria are applied to assess the worth of the models.These statistics favor models that give a good fit with fewer parameters.Based on this analysis,we find that the simplest cosmological constant model that has only one free parameter is still preferred by the current data.For other dynamical dark energy models,we find that some of them,such as the αdark energy,constant w,generalized Chaplygin gas,Chevalliear-Polarski-Linder parametrization,and holographic dark energy models,can provide good fits to the current data,and three of them,namely,the Ricci dark energy,agegraphic dark energy,and Dvali-Gabadadze-Porrati models,are clearly disfavored by the data.
LI Miao1,2,LI XiaoDong2,3 & ZHANG Xin1,4 1Kavli Institute for Theoretical Physics China,Chinese Academy of Sciences,Beijing 100190,China
The initial condition Ωde（zini）=n^2（1＋zini）^-2/4 at zini = 2000,widely used to solve the differential equation of the density of the new agegraphic dark energy（NADE） Ωde,makes the NADE model a single-parameter dark-energy cosmological model.However,we find that this initial condition is only applicable in a flat universe with only dark energy and pressureless matter.In fact,in order to obtain more information from current observational data,such as the cosmic microwave background（CMB） and the baryon acoustic oscillations（BAO）,we need to consider the contribution of radiation.For this situation,the initial condition mentioned above becomes invalid.To overcome this shortcoming,we investigate the evolutions of dark energy in matter-dominated and radiation-dominated epochs,and obtain a new initial condition de（zini）=n2（1＋zini）-2（1＋F（zini））2/4 at z ini = 2000,where F（z）≡Ωr0（1＋z）/[Ωm0＋Ωr0（1＋z）] with Ωr0 and Ωm0 being the current density parameters of radiation and pressureless matter,respectively.This revised initial condition is applicable for the differential equation of Ωde obtained in the standard Friedmann-Robertson-Walker（FRW） universe with dark energy,pressureless matter,radiation,and even spatial curvature,and can still keep the NADE model as a single-parameter model.With the revised initial condition and the observational data of type Ia supernova（SNIa）,CMB,and BAO,we finally constrain the NADE model.The results show that the single free parameter n of the NADE model can be constrained tightly.
