ELKO SPINOR MODEL WITH TORSION AND COSMOLOGY

We investigate the cosmology of ELKO spinor model when minimal coupling with torsion is included. Unlike the Dirac spinor which interacts only with the totally anti-symmetric components of torsion tensor, we find the interaction of the time component of the trace of torsion tensor with ELKO spinor provides different aspects of cosmology with fermions. We discuss a couple of cases with given potentials of ELKO spinor which can result in interesting cosmological consequences. Especially, we show that there exists an exact cosmological solution in which the universe began its acceleration only recently and this solution is an attractor. This corresponds to specific forms of torsion and potential with a mild fine-tuning which can address the coincidence problem.

AN EXACT COSMOLOGICAL SOLUTION WITH ENERGY EXCHANGE BETWEEN VACUUM AND MATTER, AND VACUUM AND RADIATION

We extend the cosmological version with energy exchange proposed by Barrow and Clifton from the case of two fluids to the case of three fluids, and find an exact cosmological solution for spatially flat Robertson–Walker metric. In this solution the integrating constants and the parameters introduced by the model are determined from cosmic observations.

Inflationary cosmological universe containing dark matter and many charged galaxies

Within the framework of Einstein's theory, cosmological universes are considered that contain three types of "fluids." A neutral cosmological fluid (dark matter), which is present everywhere, determines the overall time evolution of the universe. The second type consists of charged matter that constitutes the cores of galaxies. The electromagnetic fields generated by the charged matter make up the third kind of fluid, which is evidently null. An exact cosmological solution is furnished that provides for an early inflationary period and contains many charged black holes as galactic cores.

An oscillatory big-bang singularity

The big-bang singularities in the exact cosmological solutions of the Einstein field equations that have been studied up to now are power asymptotes in the sense that all scalar polynomials in the curvature tensor diverge monotonically as a power of clock time along the fundamental world lines, as the singularity is approached. One can thus regard the solutions as being asymptotically self-similar near the singularity. In this paper, we illustrate a more complicated type of singularity by giving an example of an exact cosmological solution in which the big-bang singularity is of an oscillatory nature, so that the solution is not asymptotically self-similar.