Nonsingular Cosmological Models Research Articles

Nonsingular cosmological models with torsion determined by vacuum polarization of quantum fields

Nonsingular cosmological models with reducing torsion induced by vacuum quantum effects are constructed. The metric of the models described corresponds to the inflationary universe. Moreover, anisotropic nonsingular cosmological model with constant torsion is constructed.

Inflation in a Bianchi type-I Einstein-Cartan cosmological model.

We present a Bianchi type-I cosmological model in the Einstein-Cartan theory of gravity. We assume that the Universe is filled in with radiation and nonzero vacuum energy (cosmological constant). Generic initial conditions lead to a nonsingular cosmological model with a finite initial radius. Singularity appears when the anisotropic energy density is greater than or equal to the spin energy density. For sufficiently large times the scale factor grows exponentially. We discuss consequences of our model in a more realistic physical situation.

Localization of the Einstein group and a nonsingular cosmological model of space-time with torsion

We consider an Einstein-invariant gauge theory of gravitation (EGT), obtained by localizing the group of motions of a homogeneous static Einstein Universe. Taking into account the cosmological term, we find exact solutions of EGT are as nonsingular homogeneous Isotropic cosmological models with both the metric and the torsion regular. It is shown that EGT satisfies the principle of correspondence with Newton's theory of gravity and with the tetrad theory of gravity in the space of absolute parallelism.

Nonsingular cosmological model with torsion induced by vacuum quantum effects

We calculated the anomalous trace of the stress—energy tensor for massless scalar and spinor fields in curved spacetime with torsion. We found that the effective action dependence of metric and torsion corresponds to a conformal anomaly. We solved the equation of motion resulting from the effective action. Metric and torsion (free from singularities) were found. The metric which was obtained in our work corresponds to the inflationary universe.

On the tetrad theory of gravity

After reviewing problems which appear in the theory of teleparallelism (tetrad theory) based on a Lagrangian quadratic in the torsion, the possibility of adding higher-order terms is discussed. For a “test Lagrangian,”O(3)-symmetric vacuum solutions and spatially homogeneous and isotropic solutions are found. The latter contain nonsingular cosmological models.

Theory of a gauged gravitational field with localization of the Einstein group

A theory of a gauged gravitational field with localization of the group of motions of a homogeneous static Einstein universe (Einstein group R x SO(4)) is formulated. Starting from the tetradic components of Einstein's universe, a relationship is established between the Riemannian metric and the gauge fields of Einstein's group. The metric connection with torsion, transforming when the gauge fields are switched off into the Christoffel connection of Einstein's universe, is found. It is shown that in the limit of infinite radius of curvature of Einsteinr's universe, the given Einstein-invariant gauge theory transforms into the tetradic theory of gravitation with localized triadic rotations. Exact solutions are obtained in the form of nonsingular cosmological models.

Nonsingular cosmological models in Brans-Dicke theory

An attempt has been made to construct nonsingular cosmological models in Brans-Dicke theory by taking vacuum field as the long-range interacting scalar field which tends to avert the occurrence of initial singularity in a homogeneous and isotropic cosmological model. Such a model will possess an extremely small value of coupling parameter ω, “as such they will be characteristically different from the usual Brans-Dicke models with ω ⩾ 6.” A justification for the estimated value of coupling parameter in the present paper has been given with particular reference to the helium problem. The model satisfies the initial conditions as proposed by Salam, Sinha, etc. However, it predicts a larger value of the energy density at the present epoch.

Interacting quantum fields in a nonsingular cosmological model

Abstract The density of massless vector bosons created in a conformally flat nonsingular cosmological model is calculated.

A non-singular quantum Universe

CLASSICAL relativistic singularities remain one of the most puzzling problems of contemporary physics. Although no consensus of opinion has been attained on their status, a great deal of work has been devoted to the search for physical mechanisms capable of eliminating the cosmological singularities, whose existence follows from the theorems of Hawking and Penrose1,2. The alternative view that the initial singularity of big-bang models is essential for the coming into being of the Universe, has also been advocated3,4. Some suggestions of cosmological singularity avoidance have recently come to light, in the ‘classical’ quantum regime (from 10−43–10−23s) (refs 5–8) or even without resorting to quantum effects9. The quantum gravitational period (t < 10−43 s) remains potentially very interesting for searching for singularity avoidance mechanisms. An interesting approach is that of quantum cosmology, based on the hamiltonian formulation of general relativity (Dirac's10 or Arnowitt, Deser and Misner's11 (ADM) method). This approach was initiated by De Witt12 and then followed by Misner13 and many others (see refs 14,15) and is used here to derive a non-singular quantum cosmological model.

Generalized ideal-fluid Lagrangian and nonsingular cosmological model of space-time

Generalized ideal-fluid Lagrangian and nonsingular cosmological model of space-time

The superfluid vacuum state, time-varying cosmological constant, and nonsingular cosmological models

Some cosmological consequences of the superfluid vacuum state developed previously by the authors are discussed, particularly with regard to the initial stages of the universe. The transition temperature of the hadronic superfluid (superfluid during the hadron era) is estimated to be 10 13 K, which is the same as the Hagedorn temperature, giving a physical basis of the thermodynamic bootstrap model.

A non-singular homogeneous universe with torsion

The Raychaudhuri equation and other relations for a spinning fluid in the framework of the Einstein-Cartan theory are obtained. It is shown that non-singular cosmological models of the Bianchi types I÷VIII are possible. As an example, a class of solutions for the I and the V type is presented.

The Flatter Regions of Newman, Unti, and Tamburino's Generalized Schwarzschild Space

The ``generalized Schwarzschild'' metric discovered by Newman, Unti, and Tamburino, which is stationary and spherically symmetric, is investigated. We find that the orbit of a point under the group of time translations is a circle, rather than a line as in the Schwarzschild case. The time-like hypersurfaces r = const which are left invariant by the group of motions are topologically three-spheres S3, in contrast to the topology S2 × R (or S2 × S1) for the r = const surfaces in the Schwarzschild case. In the Schwarzschild case, the intersection of a spacelike surface t = const and an r = const surface is a sphere S2. If σ is any spacelike hypersurface in the generalized metric, then its (two-dimensional) intersection with an r = const surface is not any closed two-dimensional manifold, that is, the generalized metric admits no reasonable spacelike surfaces. Thus, even though all curvature invariants vanish as r → ∞, in fact Rμναβ = O(1/r3) as in the Schwarzschild case, this metric is not asymptotically flat in the sense that coordinates can be introduced for which gμν − ημν = O(1/r). An apparent singularity in the metric at small values of r, which appears to be similar to the spurious Schwarzschild singularity at r = 2m, has not been studied. If this singularity should again be spurious, then the ``generalized Schwarzschild'' space would represent a terminal phase in the evolution of an entirely nonsingular cosmological model which, in other phases, contains closed spacelike hypersurfaces but no matter.