Edgard Gunzig

Thermodynamics and cosmology

A new type of cosmological history which includes large-scale entropy production is proposed. These cosmologies are based on a reinterpretation of the matter-energy stress tensor in Einsteins equations. This modifies the usual adiabatic energy conservation laws, thereby leading to a possible irreversible matter creation. This creation corresponds to an irreversible energy flow from the gravitational field to the created matter constituents. This new point of view results from the consideration of thermodynamics of open systems in the framework of cosmology. It appears that the usual initial singularity is structurally unstable with respect to irreversible matter creation. The corresponding cosmological history therefore starts from an instability of the vacuum rather than from a singularity. The universe evolves through an inflationary phase. This appears to be an attractor independent of the initial vacuum fluctuation.

Einstein frame or Jordan frame

Scalar-tensor theories of gravity can beformulated in the Jordan or in the Einstein frame, whichare conformally related. The issue of which conformalframe is physical is a contentious one; we provide a straightforward example based ongravitational waves in order to clarify theissue.

Superinflation, quintessence, and nonsingular cosmologies

The dynamics of a universe dominated by a self-interacting nonminimally coupled scalar field are considered. The structure of the phase space and complete phase portraits are given. New dynamical behaviors include superinflation (

Cosmogenesis and the origin of the fundamental length scale

\dot{H}>0

Inflationary Cosmology and Thermodynamics

), avoidance of big bang singularities through classical birth of the universe, and spontaneous entry into and exit from inflation. This model is promising for describing quintessence as a nonminimally coupled scalar field.

The dynamical system approach to scalar field cosmology

The creation of the universe is regarded as a self-consistent process in which matter is engendered by the space-time varying cosmological gravitational field and vice versa. Abundant production can occur only if the mass of the particles so created is of the order of the Planck mass (= κ−12. We conjecture that this is the origin of the fundamental length scale in field theory, as it is encountered, for example, in present efforts towards grandunification. The region of particle production is steady state in character. It ceases when the produced particles decay. The geometry of this steady state is characteristic of a de Sitter space. It permits one to estimate the number of ordinary particles presently observed, N. We find log N = O (mτdecay) = O(g−2) = O(102), with the usual estimate of g = O(10− at the Planck length scale. This is not inconsistent with the experimental estimate N ⋍ O(1090). After production, cosmological history gives way to the more conventional scheme of free expansion. The present paper is a self-contained account of our view of cosmological history and the production of matter in a varying gravitational field. Special care has been taken to describe the vacuum correctly in the present context and to perform the necessary subtractions of zero-point effects.

Conformal invariant general relativity with dynamical symmetry breakdown

We present a simple and thermodynamically consistent cosmology with a phenomenological model of quantum creation of radiation due to vacuum decay. Thermodynamics and Einsteins equations lead to an equation in which H is determined by the particle number N. The model is completed by specifying the particle creation rate , which leads to a second-order evolution equation for H. We propose a simple that is naturally defined and that conforms to the thermodynamical conditions: (i) the entropy production rate starts at a maximum; (ii) the initial vacuum (for radiation) is a non-singular regular vacuum and (iii) the creation rate is initially higher than the expansion rate H, but then falls below H. The evolution equation for H then has a remarkably simple exact solution, in which a non-adiabatic inflationary era exits smoothly to the radiation era, without a reheating transition. For this solution, we give exact expressions for the cosmic scale factor, energy density of radiation and vacuum, temperature, entropy and super-horizon scalar perturbations.

Singularities of gravity in the presence of nonminimally coupled scalar fields

A spatially flat FLRW universe (motivated by inflation) is studied; by a dimensional reduction of the dynamical equations of scalar field cosmology, it is demonstrated that a spatially flat universe cannot exhibit chaotic behaviour. The result holds when the source of gravity is a non-minimally coupled scalar field, for any self-interaction potential and for arbitrary values of the coupling constant with the Ricci curvature. The phase space of the dynamical system is studied, and regions inaccessible to the evolution are found. The topology of the forbidden regions, their dependence on the parameters, the fixed points and their stability character, and the asymptotic behaviour of the solutions are studied. New attractors are found, in addition to those known from the minimal coupling case, certain exact solutions are presented and the implications for inflation are discussed. The equation of state is not prescribed a priori , but rather is deduced self-consistently from the field equations.

Gravitational instability of empty Minkowski space-time

Abstract A conformal invariant theory of gravitation is proposed which matches General Relativity in the classical limit. It implies a dynamical origin for mass and a selection rule on “elementary” matter constituents. It is conjectured that the theory is renormalizable.

Superinflation, quintessence, and the avoidance of the initial singularity

We investigate the robustness of some recent results obtained for homogeneous and isotropic cosmological models with conformally coupled scalar fields. For this purpose, we investigate anisotropic homogeneous solutions of the models described by the action