9 research outputs found
Regular accelerating Universe without dark energy
Homogeneous isotropic cosmological models with two torsion functions filled
with scalar fields and usual gravitating matter are built and investigated in
the framework of the Poincar\'e gauge theory of gravity. It is shown that by
certain restrictions on indefinite parameters of gravitational Lagrangian the
cosmological equations at asymptotics contain an effective cosmological
constant that can explain observable acceleration of cosmological expansion.
The behavior of inflationary cosmological solutions at extremely high energy
densities is analyzed, regular bouncing solutions are obtained. The role of the
space-time torsion provoking the acceleration of cosmological expansion is
discussed.Comment: 15 pages, 16 figures, iopart class file, some additions mad
Torsion and accelerating expansion of the universe in quadratic gravitation
Several exact cosmological solutions of a metric-affine theory of gravity
with two torsion functions are presented. These solutions give a essentially
different explanation from the one in most of previous works to the cause of
the accelerating cosmological expansion and the origin of the torsion of the
spacetime. These solutions can be divided into two classes. The solutions in
the first class define the critical points of a dynamical system representing
an asymptotically stable de Sitter spacetime. The solutions in the second class
have exact analytic expressions which have never been found in the literature.
The acceleration equation of the universe in general relativity is only a
special case of them. These solutions indicate that even in vacuum the
spacetime can be endowed with torsion, which means that the torsion of the
spacetime has an intrinsic nature and a geometric origin. In these solutions
the acceleration of the cosmological expansion is due to either the scalar
torsion or the pseudoscalar torsion function. Neither a cosmological constant
nor dark energy is needed. It is the torsion of the spacetime that causes the
accelerating expansion of the universe in vacuum. All the effects of the
inflation, the acceleration and the phase transformation from deceleration to
acceleration can be explained by these solutions. Furthermore, the energy and
pressure of the matter without spin can produce the torsion of the spacetime
and make the expansion of the universe decelerate as well as accelerate.Comment: 20 pages. arXiv admin note: text overlap with gr-qc/0604006,
arXiv:1110.344