A new cosmological constant model

Abstract

We propose a new cosmological model with a time-dependent cosmological constant ($Λ\propto 1/t^2$), which starting at the Planck time as $Λ_{Pl}\sim M^2_{Pl}$, evolves to the present-day allowed value of $Λ_0\sim10^{-120}M^2_{Pl}$. This scenario is supported by non-critical string theory considerations. We compute the age of the Universe and the time-dependence of the scale factor in this model, and find general agreement with recent determinations of the Hubble parameter for substantial values of $Ω_{\rm Λ}$. This effectively low-density open Universe model differs from the traditional cosmological constant model, and has observable implications for particle physics and cosmology.