Gravitation and Cosmology最新文献

We consider a Bianchi Type I universe filled with cold dark matter and non-interacting Tsallis holographic dark energy in the framework of (f(R)) theory of gravity. We take the GO scale as an IR cutoff and find exact solutions of the field equations by considering a linearly varying deceleration parameter. The evolution of different cosmologically relevant parameters are studied graphically, and Statefinder diagnostics is performed in the light of recent cosmological observations. We find that our model corresponds to current accelerated expansion scenarios, and the function (f(R)approx R) implies that our model resembles General Relativity.

The paper considers Higgs inflation in the Jordan and Einstein pictures. In Jordan’s picture, the dynamic equations are presented in terms of the Higgs field and a superpotential. In the approximation of small field values and in the slow-rolling mode, examples of solutions are found, and verifiability by cosmological parameters is analyzed. Dynamic equations are also obtained in the Einstein picture, and a nonsingular solution is found for a weak Higgs field, whose cosmological parameters slightly differ from the observed data. To analyze the cosmological dynamics, the set of equations in Einstein’s picture is reduced to the form of an autonomous set of equations. Singular points of the dynamical system are found, and a phase portrait near these points is presented for different values of the nonminimal interaction parameter (xi). The case of large values of (xi) is also considered.

We investigate some bouncing cosmological models in an isotropic and homogeneous space-time with in (F(R)) theory of gravity. Two functional forms of (F(R)) have are studied with a bouncing scale factor. The dynamical parameters are derived and analyzed along with cosmographic parameters. A violation of sthe trong energy conditions in both bouncing models is also shown. We show that both models exhibit stable behavior with respect to cosmic time.

The effective Einstein equations on a 3-brane embedded in a 5-dimensional Riemann–Cartan bulk space-time are revisited. Addressing the shortcomings in the hitherto published junction conditions on the brane in the presence of torsion, we have elaborated on our general form of the junction conditions recently published. Applying our general junction conditions, we formulate the effective Einstein equations on a (Z_{2}) symmetric brane in a standard form highlighting the difference to those published so far.

The task of discovering the effect of gravitational waves (GWs) from high-eccentricity relativistic binary star systems (RBSS) on the vertical electric field strength in the Earth’s atmosphere near-ground layer ((E_{z})) at higher multiples of the RBSS rotation frequencies in the infralow frequency scale has been successfully solved using a signal eigenvectors’ and components’ analyzer (eigenoscope). The monitoring data at four spatially separated (E_{z}) observation stations has been used. An approach to multifrequency RBSS monitoring has been formed.

We use a single-mode squeezed thermal vacuum state formalism and examine the nature of a massive homogeneous scalar field minimally coupled to gravity in the framework of semiclassical gravity in a Bianchi type-I universe. We have obtained an estimate leading solution to the semiclassical Einstein equation for the Bianchi type-I universe showing that each scale factor in its respective direction obeys (t^{2/3}) power-law expansion. The mechanism of nonclassical thermal cosmological particle production is also analyzed in the Bianchi type-I universe.

Asymptotically exact solutions are obtained for a spherically symmetric field with the Higgs potential generated by a point scalar charge, and a method for numerical integration of the scalar field equation with the Higgs potential of a point charge is proposed. Examples of numerical modeling of the scalar field equation for a single charge are given. With the help of the solution obtained, solutions to the relativistic equations of motion of a scalar charge in an external scalar field of the Higgs type of a singular scalar source are found, and some unique properties of the scalar interaction between particles are revealed.

It is known that spatial curvature can stabilize extra dimensions in Lovelock gravity. In the present paper, we study stability of the stabilization solutions in 3rd order Lovelock gravity. We show that in the case of negative spatial curvature of extra-dimensional space, the stabilization solution is always stable. On the contrary, for positive spatial curvature, the stability depends on the coupling constant values.

We consider the metric of an axially symmetric rotating black hole. We do not specify the concrete form of a metric and rely on its behavior near the horizon only. Typically, it is characterized (in the coordinates that generalize the Boyer–Lindquist ones) by two integers (p) and (q) that enter asymptotic expansions of the time and radial metric coefficients in the main approximation. For given (p) and (q) we find a general form for which the metric is regular, and how the expansions of the metric coefficients look like. We compare two types of requirement: (i) boundedness of curvature invariants, (ii) boundedness of separate components of the curvature tensor in a freely falling frame. Analysis is done for nonextremal, extremal and ultraextremal horizons separately.

The author investigates the general Lie algebra of operators of coordinates, momenta, and Lorentz group generators, which can be used in quantum gravity, theories with a generalized uncertainty principle, double and triple relativity and theories with noncommutative space-time and momentum spaces. The structure constants of this algebra depend on the constants (c) and (h) as well as additional constants with dimensions of action ((H)), length ((L)), and mass ((M)). In the limiting case of infinite (H), (L), and (M), the algebra goes into that of operators of canonical quantum theory in Minkowski space-time. Some representations of this algebra and equations for generalized fields depending on additional fundamental physical constants are given.