A. V. Toporensky

The fate of (phantom) dark energy universe with string curvature corrections

Abstract We study the evolution of (phantom) dark energy universe by taking into account the higher-order string corrections to Einstein–Hilbert action with fixed dilaton and modulus fields. While the presence of a cosmological constant gives stable de Sitter fixed points in the cases of heterotic and bosonic strings, no stable de Sitter solutions exist when a phantom fluid is present. We find that the universe can exhibit a Big Crunch singularity with a finite time for type II string, whereas it reaches a Big Rip singularity for heterotic and bosonic strings. Thus the fate of dark energy universe crucially depends upon the type of string theory under consideration.

Big crunch avoidance in k=1 semiclassical loop quantum cosmology

It is well known that a closed universe with a minimally coupled massive scalar field always collapses to a singularity unless the initial conditions are extremely fine tuned. We show that the corrections to the equations of motion for the massive scalar field, given by loop quantum gravity in high curvature regime, always lead to a bounce independently of the initial conditions. In contrast to the previous works in loop quantum cosmology, we note that the singularity can be avoided even at the semi-classical level of effective dynamical equations with non-perturbative quantum gravity modifications, without using a discrete quantum evolution.

Reconstruction and deceleration–acceleration transitions in modified gravity

We discuss the cosmological reconstruction in modified Gauss–Bonnet and F(R) gravities. Two alternative representations of the action (with and without auxiliary scalar) are considered. The approximate description of deceleration–acceleration transition cosmologies is reconstructed. It is shown that cosmological solution containing Big Bang and Big Rip singularities may be reconstructed only using the representation with the auxiliary field. The analytical description of the deceleration–acceleration transition cosmology in modified Gauss–Bonnet gravity is demonstrated to be impossible at sufficiently general conditions.

Cosmological dynamics of non-minimally coupled scalar field system and its late time cosmic relevance

We investigate the cosmological dynamics of non-minimally coupled scalar field system described by

Simplest Cosmological Model with the Scalar Field

F(\phi)R

A NOTE ON DIFFERENCES BETWEEN (4+1)- AND (5+1)-DIMENSIONAL ANISOTROPIC COSMOLOGY IN THE PRESENCE OF THE GAUSS–BONNET TERM

coupling with

Exact exponential solutions in Einstein–Gauss–Bonnet flat anisotropic cosmology

F(\phi)=(1-\xi\phi^N)R

Dynamical features of scalar-torsion theories

(

Nature of singularities in anisotropic string cosmology

N\ge2

Complex inflaton field in quantum cosmology

) and the field potential,