Non Singular Origin of the Universe and its Present Vacuum Energy Density Academic Article uri icon

abstract

  • We consider a nonsingular origin for the universe starting from an Einstein static universe, the so-called "emergent universe" scenario, in the framework of a theory which uses two volume elements &surd; {-{g}}d4x and Phid4x, where Phi is a metric independent density, used as an additional measure of integration. Also curvature, curvature square terms and for scale invariance a dilaton field varphi are considered in the action. The first-order formalism is applied. The integration of the equations of motion associated with the new measure gives rise to the spontaneous symmetry breaking of scale invariance. After spontaneous symmetry breaking of scale invariance it is found that a nontrivial potential for the dilaton is generated. In the Einstein frame we also add a cosmological term that parametrizes the zero point fluctuations. The resulting effective potential for the dilaton contains two flat regions, for varphi --> ∞ relevant for the nonsingular origin of the universe, followed by an inflationary phase and varphi --> - ∞, describing our present universe. The dynamics of the scalar field becomes nonlinear and these nonlinearities are instrumental in the stability of some of the emergent universe solutions, which exists for a parameter range of values of the vacuum energy in varphi --> - ∞, which must be positive but not very big, avoiding the extreme fine tuning required to keep the vacuum energy density of the present universe small. Zero vacuum energy density for the present universe defines the threshold for the creation of the universe.

publication date

  • January 1, 2011