Phantom dark energy and cosmological solutions without the Big Bang singularity

Abstract

The hypothesis is rapidly gaining popularity that the dark energy pervading our universe is extra-repulsive ($-p>ρ$). The density of such a substance(usually called phantom energy) grows with the cosmological expansion and may become infinite in a finite time producing a Big Rip. In this Letter we analyze the late stages of the universe evolution and demonstrate that the presence of the phantom energy in the universe is not enough in itself to produce the Big Rip. This singularity occurrence requires the fulfillment of some additional, rather strong conditions. A more probable outcome of the cosmological evolution is the decay of the phantom field into 'normal' matter. The second, more intriguing consequence of the presence of the phantom field is the possibility to introduce a cosmological scenario that does not contain a Big Bang. In the framework of this model the universe eternally expands, while its density and other physical parameters oscillate over a wide range, never reaching the Plank values. Thus, the universe evolution has no singularities at all.