DIRACS COSMOLOGY WITH VARYING COSMOLOGICAL CONSTANT

The phenomenological approach to investigating the decay of the vacuum energy density is generalized in the spirit of Dirac's large number hypothesis. Different arguments are outlined to justify an universal dependence of the type Lambda = beta H-2 (beta is a pure number and H is the Hubble parameter). Such time-varying Lambda does change the predictions of the earlier Dirac's cosmology. The deceleration parameter (q(0) = (2 - beta)/(1 + beta)) and the age parameter (H(0)t(0) = (1 + beta)/3) are now compatible with the observations. The model also allows a ''power-law'' inflationary phase and a rate of matter creation smaller than the one present in the steady state universe.