A new cosmological constant model

We propose a new cosmological model with a time-dependent cosmological constant ($\mathrm{\Lambda }\propto 1\mathrm{/}{t}^2$), which starting at the Planck time as ${\mathrm{\Lambda }}_{Pl}\sim M_{Pl}^2$, evolves to the present-day allowed value of ${\mathrm{\Lambda }}_0\sim {10}^{-120}{M}_{Pl}^2$. 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 ${\mathrm{\Omega }}_{\mathrm{\Lambda }}$. This effectively low-density open Universe model differs from the traditional cosmological constant model, and has observable implications for particle physics and cosmology.