Time variable cosmological constants from the age of universe

In this Letter, time variable cosmological constant, dubbed age cosmological constant, is investigated motivated by the fact: any cosmological length scale and time scale can introduce a cosmological constant or vacuum energy density into Einstein's theory. The age cosmological constant takes the form ρΛ=3c2MP2/tΛ2, where tΛ is the age or conformal age of our universe. The effective equation of state (EoS) of age cosmological constant are wΛeff=−1+23ΩΛc and wΛeff=−1+23ΩΛc(1+z) when the age and conformal age of universe are taken as the role of cosmological time scales respectively. The EoS are the same as the so-called agegraphic dark energy models. However, the evolution histories are different from the agegraphic ones for their different evolution equations.