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 h ypothesis. Different arguments are outlined to justify an universal de pendence 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 predi ctions of the earlier Dirac's cosmology. The deceleration parameter (q (0) = (2 - beta)/(1 + beta)) and the age parameter (H(0)t(0) = (1 + be ta)/3) are now compatible with the observations. The model also allows a ''power-law'' inflationary phase and a rate of matter creation smal ler than the one present in the steady state universe.