LRS Bianchi type-I models with a time-dependent cosmological "constant" - art. no. 063507.

Plane symmetric homogeneous models of the universe with a perfect fluid dis tribution of matter and a variable cosmological "constant" representing the energy density of vacuum have been presented. The models are highly anisot ropic in the early stages of evolution and ultimately evolve to the standar d model at the present epoch. Of the three models obtained in this paper, o ne has an increasing vacuum energy density with time in the early universe. Though highly negative in the very early universe, the vacuum density soon becomes positive, and meets the observational limits at the present epoch. The negative vacuum in the early universe in this model, which decays nume rically, adds up to anisotropy and at the same time contributes to the isot ropization process. The second model is found to admit matter creation from the decaying Vacuum energy whereas the third one, in which the vacuum dens ity is always one third of the corresponding radiation density, is devoid o f any such creation. [S0556-2821(99)01616-1].