Interplay between gravity and quintessence: a set of new GR solutions (original) (raw)
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Physics Letters A, 1991
We present the field equations of gravitation, the spherically symmetric solution ofwhich in pseudo-Euclidean space-time has no physical singularity.
Eprint Arxiv Physics 0606155, 2006
The third logically consistent and more rational space-time theory…..…………(4) 3. The Rationality Problems of the Principles of Equivalence and General Relativity...….…………………………......(13) 4. Singularities Appearing in the Gravitational Fields of Thin Circle and Double Spheres and the Rationality Problem of the Einstein's Equations of Gravitational Fields……………………………...……......(25) 5. Revised Formulas of Newtonian Gravity Based on the Schwarzschild Solution of the Einstein's Equation of Gravitation fields………….......(39) 6. The Gravitational Theory Established in Flat Space-time...…………..(62) 7. The Cosmological theory Established in Flat Space-time……………..(67) Authors who are not interested in the concept analysis of space-time and gravitation can start from Section 4 after reading introduction By the coordinate transformations of the Kerr and Kerr-Newman solutions, the solutions for the static distributions of mass thin loop and double spheres with axial symmetry are obtained. The results indicate that no matter what the masses and the densities of thin loop and double spheres are, the space's curvatures in the centre points of loop and the double sphere's connecting line are infinite. The singularity points are completely exposed in vacuum. The space curvatures nearby the singularity points and the surfaces of thin loop as well as double spheres are also highly curved even though the gravitational fields are very weak. It is obvious that all of them are actually impossible. The results show that the space-time singularities appearing in the Einstein's theory of gravity are not caused by the high density and huge mass's distributions. They are caused actually by the descriptive method of curved space-time, having nothing to do with the real world. After the geodesic equation described by the Schwarzschild solution of the Einstein's equation of gravitational field is transformed into flat reference frame to describe, all space-time singularities are transformed into the infinite points of gravitations. This kind of infinites would appear in all theories based on the mode of point particles and not worth to be surprise. So we should give up the descriptive method of geometry, retuning to the classical descriptive method of dynamics and interaction for gravitation.
Modified Gravity and Coupled Quintessence
Lecture Notes in Physics, 2014
The distinction between modified gravity and quintessence or dynamical dark energy is difficult. Many models of modified gravity are equivalent to models of coupled quintessence by virtue of variable transformations. This makes an observational differentiation between modified gravity and dark energy very hard. For example, the additional scalar degree of freedom in f (R)-gravity or non-local gravity can be interpreted as the cosmon of quintessence. Nevertheless, modified gravity can shed light on questions of interpretation, naturalness and simplicity. We present a simple model where gravity is modified by a field dependent Planck mass. It leads to a universe with a cold and slow beginning. This cosmology can be continued to the infinite past such that no big bang singularity occurs. All observables can be described equivalently in a hot big bang picture with inflation and early dark energy.
Quintessence and cosmic acceleration
A cosmological model with perfect fluid and self-interacting quintessence field is considered in the framework of the spatially flat Friedmann-Robertson-Walker (FRW) geometry. By assuming that all physical quantities depend on the volume scale factor of the Universe, the general solution of the gravitational field equations can be expressed in an exact parametric form. The quintessence field is a free parameter. With an appropriate choice of the scalar field a class of exact solutions is obtained, with an exponential type scalar field potential fixed via the gravitational field equations. The general physical behavior of the model is consistent with the recent cosmological scenario favored by supernova type Ia observations, indicating an accelerated expansion of the Universe. *
Singularity-free cosmological solutions in quadratic gravity
Physical Review D, 1999
We study a general field theory of a scalar field coupled to gravity through a quadratic Gauss-Bonnet term xi(phi)R2GB\xi(\phi) R^2_{GB}xi(phi)R2GB. The coupling function has the form xi(phi)=phin\xi(\phi)=\phi^nxi(phi)=phin, where nnn is a positive integer. In the absence of the Gauss-Bonnet term, the cosmological solutions for an empty universe and a universe dominated by the energy-momentum tensor of a scalar field are always characterized by the occurrence of a true cosmological singularity. By employing analytical and numerical methods, we show that, in the presence of the quadratic Gauss-Bonnet term, for the dual case of even nnn, the set of solutions of the classical equations of motion in a curved FRW background includes singularity-free cosmological solutions. The singular solutions are shown to be confined in a part of the phase space of the theory allowing the non-singular solutions to fill the rest of the space. We conjecture that the same theory with a general coupling function that satisfies certain criteria may lead to non-singular cosmological solutions.
Patrik Sandin Cosmological Models and Singularities in General Relativity
2011
This is a thesis on general relativity. It analyzes dynamical properties of Einstein’s field equations in cosmology and in the vicinity of spacetime singularities in a number of different situations. Different techniques are used depending on the particular problem under study; dynamical systems methods are applied to cosmological models with spatial homogeneity; Hamiltonian methods are used in connection with dynamical systems to find global monotone quantities determining the asymptotic states; Fuchsian methods are used to quantify the structure of singularities in spacetimes without symmetries. All these separate methods of analysis provide insights about different facets of the structure of the equations, while at the same time they show the relationships between those facets when the different methods are used to analyze overlapping areas. The thesis consists of two parts. Part I reviews the areas of mathematics and cosmology necessary to understand the material in part II, whi...