Nonlinear Spinor Fields and its role in Cosmology

Different characteristic of matter influencing the evolution of the Universe has been simulated by means of a nonlinear spinor field. Exploiting the spinor description of perfect fluid and dark energy evolution of the Universe given by an anisotropic Bianchi type-VI, VI$_0$, V, III, I or isotropic Friedmann-Robertson-Walker (FRW) one has been studied. It is shown that due to some restrictions on metric functions, initial anisotropy in the models Bianchi type-VI, VI$_0$, V and III does not die away, while the anisotropic Bianchi type-I models evolves into the isotropic one.Comment: 22 pages, 12 Figure

Structural instability of Friedmann-Robertson-Walker cosmological models

Cosmological singularity and asymptotic behaviour of scale factor of generalized cosmological models are analyzed in respect of their structural stability. It is shown, that cosmological singularity is structurally unstable for the majority of models with barotropic perfect fluid with strong energy condition. Inclusion of Lambda-term extends the set of structurally stable cosmological models.Comment: 14 pages, 4 figures in TeXCad, developed version of talk, presented at XIII Russian Gravitational Conference, June 2008, to be published in GRG, minor changes concerning added reference

Bianchi type-I model with cosmic string in the presence of a magnetic field: spinor description

A Bianchi type-I cosmological model in the presence of a magnetic flux along a cosmic string is investigated. A nonlinear spinor field is used to simulate the cosmological cloud of strings. It is shown that the spinor field simulation offer the possibility to solve the system of Einstein's equation without any additional assumptions. It is shown that the present model is nonsingular at the end of the evolution and does not allow the anisotropic Universe to turn into an isotropic one.Comment: 14 pages, 4 figures, new figus are added, singularity and isotropization process are discussed in detai

Spinor model of a perfect fluid and their applications in Bianchi type-I and FRW models

Different characteristic of matter influencing the evolution of the Universe has been simulated by means of a nonlinear spinor field. Exploiting the spinor description of perfect fluid and dark energy evolution of the Universe given by an anisotropic Bianchi type-I (BI) or isotropic Friedmann-Robertson-Walker (FRW) one has been studied.Comment: 10 pages, 8 Figure

Rotating cylindrical wormholes and energy conditions

We seek wormholes among rotating cylindrically symmetric configurations in general relativity. Exact wormhole solutions are presented with such sources of gravity as a massless scalar field, a cosmological constant, and a scalar field with an exponential potential. However, none of these solutions are asymptotically flat, which excludes the existence of wormhole entrances as local objects in our Universe. To overcome this difficulty, we try to build configurations with flat asymptotic regions using the cut-and-paste procedure: on both sides of the throat, a wormhole solution is matched to a properly chosen region of flat space-time at some surfaces ∑- and ∑+. It is shown, however, that if the source of gravity in the throat region is a scalar field with an arbitrary potential, then one or both thin shells appearing on ∑- and ∑+ inevitably violate the null energy condition. Thus, although rotating wormhole solutions are easily found without exotic matter, such matter is still necessary for obtaining asymptotic flatness. © 2016 World Scientific Publishing Company

Rotating cylindrical wormholes and energy conditions

We seek wormholes among rotating cylindrically symmetric configurations in general relativity. Exact wormhole solutions are presented with such sources of gravity as a massless scalar field, a cosmological constant, and a scalar field with an exponential potential. However, none of these solutions are asymptotically flat, which excludes the existence of wormhole entrances as local objects in our Universe. To overcome this difficulty, we try to build configurations with flat asymptotic regions using the cut-and-paste procedure: on both sides of the throat, a wormhole solution is matched to a properly chosen region of flat space-time at some surfaces ∑- and ∑+. It is shown, however, that if the source of gravity in the throat region is a scalar field with an arbitrary potential, then one or both thin shells appearing on ∑- and ∑+ inevitably violate the null energy condition. Thus, although rotating wormhole solutions are easily found without exotic matter, such matter is still necessary for obtaining asymptotic flatness. © 2016 World Scientific Publishing Company

Potentially observable cylindrical wormholes without exotic matter in general relativity

All known solutions to the Einstein equations describing rotating cylindrical wormholes lack asymptotic flatness in the radial directions and therefore cannot describe wormhole entrances as local objects in our Universe. To overcome this difficulty, wormhole solutions are joined to flat asymptotic regions at some surfaces Σ- and Σ+. The whole configuration thus consists of three regions, the internal one containing a wormhole throat, and two flat external ones, considered in rotating reference frames. Using a special kind of anisotropic fluid respecting the weak energy condition (WEC) as a source of gravity in the internal region, we show that the parameters of this configuration can be chosen in such a way that matter on both junction surfaces Σ- and Σ+ also respects the WEC. Closed timelike curves are shown to be absent by construction in the whole configuration. It seems to be the first example of regular twice (radially) asymptotically flat wormholes without exotic matter and without closed timelike curves, obtained in general relativity. © 2019 American Physical Society

Rotating cylindrical wormholes

We consider stationary, cylindrically symmetric configurations in general relativity and formulate necessary conditions for the existence of rotating cylindrical wormholes. It is shown that in a comoving reference frame, the rotational part of the gravitational field is separated from its static part and forms an effective stress-energy tensor with exotic properties, which favors the existence of wormhole throats. Exact vacuum and scalar-vacuum solutions (with a massless scalar) are considered as examples, and it turns out that even vacuum solutions can be of wormhole nature. However, solutions obtainable in this manner cannot have well-behaved asymptotic regions, which excludes the existence of wormhole entrances appearing as local objects in our Universe. To overcome this difficulty, we try to build configurations with flat asymptotic regions by the cut-and-paste procedure: on both sides of the throat, a wormhole solution is matched to a properly chosen region of flat space at surfaces Σ- and Σ+. It is shown, however, that if we describe the throat region with vacuum or scalar-vacuum solutions, one or both thin shells appearing on Σ- and Σ+ inevitably violate the null energy condition. In other words, although rotating wormhole solutions are easily found without exotic matter, such matter is still necessary for obtaining asymptotic flatness. © 2013 American Physical Society

Quantum cosmology with scalar-vector and scalar-spinor interactions

The problem of matter creation in the early Universe is considered in terms of quantum cosmology, introducing interactions of the scalar field with the spinor and vector fields of matter

A homogeneous multicomponent cosmological model with interacting spinor, scalar, and vector fields in the presence of dark energy

The evolution of a homogeneous multicomponent cosmological model with interacting spinor, vector, and scalar fields in the presence of dark energy described by the ideal liquid with the corresponding state equation is considered. The source of the vector and spinor fields is the kinetic energy of the inflation (scalar) field that is modeled by introduction of Lagrangians for the spinor and vector fields interacting with the scalar field through the squared gradient. A system of the dynamic Einstein-Proca-Klein-Fock and ideal liquid equations in the presence of interaction of the cosmological model components is solved. The role of individual components in the process of model evolution is elucidated. © 2009 Springer Science+Business Media, Inc