Singularity-free Cosmology Research Articles

BOUNCING BRANEWORLD WITH BORN–INFELD AND GAUSS–BONNET

We show the existence of some bouncing cosmological solutions in the braneworld scenario. More specifically, we consider a dynamical three-brane in the background of Born–Infeld and electrically charged Gauss–Bonnet black hole. We find that, in certain range of parameter space, the brane universe, at least classically, never shrinks to a zero size, resulting in a singularity-free cosmology within the classical domain.

A kind of singularity-free cosmology model

According to Penrose-Hawkings theorem on the singularity of cosmology，the singularity exists in the case when the source havs no rotation or acceleration，and the energy density satisfies the condition ρ+3p≥0. In this paper we study some singularity-free cosmological models under the conditions that the source has rotation. Some cosmological solutions without singularity are obtained.

Exact cosmological solutions from conservation laws and induced gravity matched with observational data

We discuss, in the framework of induced gravity, singularity free cosmologies, deriving a class of exact solutions depending on the form of gravitational coupling and of interaction potential. The basic principle from which such cosmologies are derived, is the fact that, in a more general theory, cosmological singularities can be removed considering conservation laws always and absolutely valid. It is very important to stress that we find a fine agreement among the solutions and the data coming from all recent observational campaigns.

SINGULARITY FREE SOLUTIONS FROM SCALAR-TENSOR GRAVITY COMPARED WITH RECENT COSMOLOGICAL OBSERVATIONS

Singularity free cosmologies, depending on the form of gravitational coupling and interaction potential, are derived in the framework of (n+1)-dimensional scalar-tensor theories of gravity. The results are matched with cosmological observations giving rise to realistic scenarios where the observed acceleration of cosmic fluid is recovered. Furthermore, being the solutions singularity free, the approach could work also at early epochs showing a general validity of the model.

The graceful exit in string cosmology

We re-examine the graceful exit problem in the pre-big bang scenario of string cosmology, by considering the most general time-dependent classical correction to the Lagrangian with up to four derivatives. By including possible forms for quantum loop corrections we examine the allowed region of parameter space for the coupling constants which enable our solutions to link smoothly the two asymptotic low-energy branches of the pre-big bang scenario, and observe that these solutions can satisfy recently proposed entropic bounds on viable singularity free cosmologies.

Early universe evolution in graviton-dilation models

We present a class of graviton-dilaton models which leads to a singularity free evolution of the universe. We study the evolution of a homogeneous isotropic universe. We follow an approach which enables us to analyse the evolution and obtain its generic features even in the absence of explicit solutions, which are not possible in general. We describe the generic evolution of the universe and show, in particular, that it is singularity free in the present class of models. Such models may stand on their own as interesting models for singularity free cosmology, and may be studied accordingly. They may also arise from string theory. We discuss critically a few such possibilities.

Freezing of the Affine Gravity and Singularity Free Cosmological Models

A modified version of the Einstein theory of gravity is proposed in which the constant G is dynamical, that is dependent on the energy stress tensor. This permits one to obtain a model in which the Planck's energy density is unbounded, meaning that gravity never reaches the condition ρ>ρ P . This permits one to separate the affine description from the quantum one, which has recently been observed not to be completely compatible. We describe moreover how this can bring us to violate the strong energy condition so as to avoid the constraints of singularity theorems.

Singularity-Free Homogeneous Isotropic Universe in Graviton-Dilaton Models

We present a class of graviton-dilaton models in which a homogeneous isotropic universe, such as our observed one, evolves with no singularity at any time. Such models may stand on their own as interesting models for singularity free cosmology, and may be studied further accordingly. They may also arise from string theory. We discuss critically a few such possibilities.

The ?-field theory of gravitation and cosmology

The present paper presents, within the Einstein conceptual framework, a scalar field theory of gravitation. The Ω-field, however, is not superimposed on the space-time manifold from outside the given geometry but is derived from the space-time torsion which is shown to be the generator of gravitation and inertia as well as spin. The theory predicts the three crucial tests of gravitation to the same degree of accuracy as does Einstein's theory. But it also predicts gravitational radiation emitted by a pulsating sphere and a singularity free cosmology in contradiction to Einstein's results. Above all, the scalar gravitational field can be easily quantized in the present context.

Scalar trace anomaly and anti-gravitational interaction in a perturbative approach to self-consistent cosmologies

We present a perturbative approach to the equations controlling the behavior of the recently proposed self-consistent, causal, singularity-free cosmologies. This approach sheds a new light on the threshold mass which governs both the (in)stability of empty Minkowski space and the existence of these cosmologies. An unexpected fact arises at the lower order of this perturbative scheme: the mass of the massive (scalar) field coupled non-minimally to gravitation is completely absorbed in a rescaling of the gravitational constant. The latter becomes negative, thereby causing an effective anti-gravitational interaction when the corresponding mass exceeds the minkowskian instability threshold. Moreover, the source of this effective antigravitational interaction is the usual scalar trace anomaly associated with the residual massless part of the matter field.