Singularity-free Cosmological Model Research Articles

Perturbations in a singularity-free cosmological model.

view Abstract Citations (8) References (10) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Perturbations in a Singularity-free Cosmological Model Israelit, Mark ; Rosen, Nathan Abstract The work is based on a singularity-free model of the universe previously proposed by the authors. According to this model, at the beginning of the present expansion phae the universe was filled with prematter for which P = -rho, and rho is about rho(p), the Planck density, and the prematter went over to ordinary matter in the course of time. Two approaches are considered. In the first it is assumed that there are initial perturbations in the prematter. These grow tremendously in the course of time. In the second it is assumed that the prematter has no perturbations, but that perturbations develop as the prematter is converted to ordinary matter. Publication: The Astrophysical Journal Pub Date: July 1991 DOI: 10.1086/170207 Bibcode: 1991ApJ...375..463I Keywords: Astronomical Models; Density Distribution; Gauge Theory; Perturbation Theory; Relativity; Universe; Astrophysics; COSMOLOGY; EARLY UNIVERSE; RELATIVITY full text sources ADS |

A quantum cosmological model based on Einstein's universe

The conformal factor and a massless scalar field are quantized on Einstein background spacetime. A singularity-free cosmological model is obtained and discussed.

A singularity-free cosmological model in general relativity

view Abstract Citations (62) References (9) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Singularity-free Cosmological Model in General Relativity Israelit, Mark ; Rosen, Nathan Abstract A cosmological model is proposed in the framework of Einstein's general relativity theory which is free from the singularity, flatness, homogeneity and isotropy, and horizon problems which afflict the standard cosmological model. The present model describes a nonsingular closed universe initially filled with 'prematter' characterized by a density rho euqal to the Planck density and a pressure P = -rho. The universe undergoes a very rapid expansion in the course of which there is a transition from the prematter period to the radiation-dominated period. These periods and the transition between them are described by a single equation of state. When the radiation period is reached, the universe behaves as if it had started from the big bang. Thereafter its behavior is like that of the standard model. Publication: The Astrophysical Journal Pub Date: July 1989 DOI: 10.1086/167622 Bibcode: 1989ApJ...342..627I Keywords: Astronomical Models; Relativity; Singularity (Mathematics); Computational Astrophysics; Equations Of State; Universe; Astrophysics; COSMOLOGY; EARLY UNIVERSE; RELATIVITY full text sources ADS |

A singularity-free cosmological model in ECSK theory

In the framework of the ECSK [Einstein-Cartan-Sciama-Kibble] theory of cosmology, a scalar field nonminimally coupled to the gravitational field is considered. For a Robertson-Walker open universe (k=0) in the radiation era, the field equations admit a singularity-free solution for the scale factor. In theory, the torsion is generated through nonminimal coupling of a scalar field to the gravitation field. The nonsingular nature of the cosmological model automatically solves the flatness problem. Further absence of event horizon and particle horizon explains the high degree of isotropy, especially of 2.7-K background radiation.

Vacuum Polarization and Scalar Field Effects in the Early Universe

Talcing into account vacuum polarization effects and a coherent massive scalar field we consider a singularity free cosmological model from which an intermediate inflationary stage follows quite naturally. According to the ideas of Tryon, Fomin, Zeldovich and others on the spontaneous creation of an universe by a quantum process the newly created universe must be closed. Its evolution starts from a finite initial value a of the order of the Planck length with a zero velocity ho = 0 (h - Hubble parameter). Therefore, in this moment an effective source term not fulfilling the strong energy condition must be dominant. It can originate fron a coherent massive scalar field (mass m) with zero kinetic energy and/or the vacuum polarization (considered here in the form of a modified gravitational Lagrangian with quadratic terms of the Ricci scalar). The corresponding general Lagrangian reads (c = h =1) where ∝ is a negative coupling constant and Lmat is the Lagrangian of other possible existing matter. Both the massive scalar field and the vacuum polarization effects drive the universe to expand exponentially for a definite time interval depending on the initial radius a0 and the parameters m and ∝, during which all other matter being originally present is diluted. The following small oscillations superimposed on the dust-like power law behaviour of the scale factor cause an intensive particle production, and the universe heats up to a radiation dominated Friedmann universe. This process must terminate before baryogenesis. The matching of the different phases of the cosmological evolution and the requirement to fit the parameters of the observed universe lead to a definite parameter range for m and |∝| well below the Planck values. In consequence the present mass density must be equal to the critical one (Ω = 1) with high accuracy.

Quantum cosmological model with a scalar field as source

It is shown that if both the conformal factor and scalar field are quantized on a background spacetime, a singularity-free cosmological model can be obtained and the quantum states must be zero-energy ones.

A Finite Temperature λϕ4 Model and De Sitter-Friedmann Phase Transition in the Early Universe

In this paper, we propose a simple finite temperature λϕ4 cosmological model to show that a new type singularity free cosmological model could be established by taking a series of important quantum and statistical effects into consideration such as spontaneous symmetry breaking, trace anomaly and particle creation, symmetry restoration at high temperature through phase transition and others. To begin with, the state of the universe would be a cold singu1arity free and horizon free Beltrami-Anti de Sitter one rather than a hot one. Then associated with the, particle creation, the temperature would, become higher and higher and as soon. as the temperature reached a critical value, Tc, a second-order phase transition would take place and the universe would transfer to a hot radiation dominated Friedmann state.

Is the cosmological singularity compulsory

The cosmological singularity is inherent in all conventional general relativistic cosmological models. There can be no question that it is an unphysical feature; yet there does not seem to be any convervative way of eliminating it. Here we present singularity-free isotropic cosmological models which are indistinguishable from general relativistic ones at late times. They are based on the general theory of variable rest masses that we developed recently. Outside cosmology this theory simulates general relativity well. Thus it provides a framework incorporating those features which have made geneal relativity so sucessful while providing a way out of singularity dilemma. The cosmological models can be made to incorporate Dirac's large numbers hypothesis. G(now)/G(0)approx.10/sup -38/.