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Abstract: The property of dark energy and the physical reason for acceleration of thepresent universe are two of the most difficult problems in modern cosmology.The dark energy contributes about two-thirds of the critical density of thepresent universe from the observations of type-Ia supernova SNe Ia andanisotropy of cosmic microwave background CMB.The SN Ia observations alsosuggest that the universe expanded from a deceleration to an acceleration phaseat some redshift, implying the existence of a nearly uniform component of darkenergy with negative pressure. We use the ``gold- sample containing 157 SNe Iaand two recent well-measured additions, SNe Ia 1994ae and 1998aq to explore theproperties of dark energy and the transition redshift. For a flat universe withthe cosmological constant, we measure $\Omega {M}=0.28 {-0.05}^{+0.04}$, whichis consistent with Riess et al. The transition redshift is$z {T}=0.60 {-0.08}^{+0.06}$. We also discuss several dark energy models thatdefine the $wz$ of the parameterized equation of state of dark energyincluding one parameter and two parameters $wz$ being the ratio of thepressure to energy density. Our calculations show that the accuratelycalculated transition redshift varies from $z {T}=0.29 {-0.06}^{+0.07}$ to$z {T}=0.60 {-0.08}^{+0.06}$ across these models. We also calculate the minimumredshift $z {c}$ at which the current observations need the universe toaccelerate.



Autor: F. Y. Wang, Z. G. Dai NJU

Fuente: https://arxiv.org/



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