Gravitation and Cosmology最新文献

We study the nonrelativistic Schrödinger wave equation under the influence of a quantum flux field with an interaction potential in the background of a pointlike global monopole (PGM). In fact, we consider an inverse quadratic Yukawa plus inverse square potential and derive the radial equation employing the Greene–Aldrich approximation scheme in the centrifugal term. We determine the approximate eigenvalue solution using the parametric Nikiforov–Uvarov method and analyze the result. Afterwards, we derive the radial wave equation using the same potential employing a power series expansion method in the exponential potential and solve it analytically. We show that the energy eigenvalues are shifted by the topological defects of a pointlike global monopole as compared to the flat space result. In addition, we see that the energy eigenvalues depend on the quantum flux field that shows an analogue to the Aharonov–Bohm effect.

This study is an investigation of exact cosmological models in modified (f(R,L_{m})) gravity with observational constraints, where (R) is the Ricci scalar, and (L_{m}) is the matter Lagrangian for a perfect fluid. We have obtained the field equations using a flat FLRW metric with matter Lagrangian (L_{m}=-p) and (f(R,L_{m})=R/2+alpha L_{m}^{n}-beta), where (alpha), (beta), (n) are positive parameters. We have solved the field equations for the scale factor (a(t)) with the equation of state (EoS) (p=omegarho), where (p) is the isotropic pressure and (rho) is the energy density. We have obtained the scale factor (a(t)=k_{0}[sinh(k_{1}t+k_{2})]^{[2(n+omega-nomega]/[3n(1+omega)]}), where (k_{1}=frac{sqrt{3beta}}{2}frac{n(1+omega)}{n+omega-nomega}), and (k_{0}), (k_{2}) are integration constants. Using this scale factor, we have analyzed various cosmological parameters ({H_{0},q_{0},j_{0},s_{0},t_{0}}) with observational constraints by applying the (chi^{2}) test with four observational datasets (H(z)), Union 2.1, JLA and Bined datasets. Also, we have analyzed the Om diagnostic parameter.

Equations of motion of spinning density for extended objects and tthe corresponding deviation equations are derived. The problem of motion for a variable mass of a spinning extended object is obtained. Spinning fluids may be considered as a special case to express the motion of spinning density for extended objects. Meanwhile, the spinning density tensor can be expressed in terms of the tetrad formalism of general relativity to be regarded as a gauge theory of gravity. The equations of spinning and spinning deviation density tensors have been derived using a specific type of Bazanski Lagrangian.

We demonstrate a new anisotropic solution to the Einstein field equations in Finch–Skea space-time. The physical features of a stellar configuration have been studied in previous investigations. We create a model that meets all physical plausibility conditions for a variety of stars and plot graphs for 4U 1820-30.

The possibility of geometrization of the gravitational and electromagnetic fields in 4D Finsler space (the Model of Embedded Spaces—MES) is investigated. The model postulates a proper metric set of an element of distributed matter and asserts that space-time is a mutual physical embedding of such sets. The simplest MES geometry is constructed (its relativistic Finsler version) with a connection that depends on the properties of matter and its fields (torsion and nonmetricity are absent). The field hypothesis and the Least Action Principle of the matter-field system lead to Einstein-type and Maxwell-type equations, and their nonlinearity to the anisotropic field contribution to the seed mass of matter. It is shown that the seed matter plays the role of a physical vacuum of the Embedding and determines the cosmological constant. In the special case of a conformal metric, the Maxwell-type equations reduce to the Maxwell equations themselves and a negative electromagnetic contribution. A possible experimental verification of this result is evaluated. The “redshift” effect in an electric field is also mentioned as a method for studying the vacuum and a relic electric charge. A study of the gauge structure of the presented theory is postponed to the future.

The evolution of a quantized electromagnetic mode in a space-time toy model with nontrivial topology, allowing closed timelike and null world lines, is considered. The physical consequences of adopting an ontological or epistemological view on a quantum state are compared. It is done within a framework of two alternative interpretations of mode evolution—Deutsch’s D-CTC model (ontological) and S-CTC model (epistemological). The future states of the mode (with respect to the causal loop) are calculated for two types of interaction with the mode’s previous version coming from the future. The found differences of the predictions may be helpful for building a future fundamental theory unifying quantum physics and gravity.

We study embedding gravity, a modified theory of gravity in which our space-time is assumed to be a four-dimensional surface in flat ten-dimensional space. Based on a simple geometric idea, this theory can be reformulated as general relativity with additional degrees of freedom and a contribution to action which can be interpreted as describing dark matter. We study the canonical formalism for such a formulation of embedding gravity. After solving simple constraints, the Hamiltonian is reduced to a linear combination of four first-class constraints with Lagrange multipliers. There still remain six pairs of second-class constraints. Possible ways of taking these constraints into account are discussed. We show that one way of solving the constraints leads to a canonical system going into the previously known canonical formulation of the complete embedding theory with an implicitly defined constraint.

We present constraints on the deceleration ((q)) and jerk ((j)) parameters using the late-time integrated Sachs-Wolfe effect, type Ia supernovae, and (H(z)) data . We first directly measure the deceleration and jerk parameters using the cosmic chronometers data with the Taylor series expression of (H(z)).However, due to the unusual variations in the deceleration parameter with slight changes in other parameters like snap ((s)) and lerk ((l)), we found that direct measurements using the series expansion of (H(z)) is not a suitable method for non-(Lambda)CDM models, and so we will need to derive the deceleration parameter after constraining the density parameters and dark energy equation of state. Then we present the derived values of the deceleration parameter from the (Lambda)CDM, WCDM and CPL models. We also discuss the transition redshift (z_{t}) in relation with the deceleration parameter. Our best fit values for the deceleration parameter, after combining results from (H(z)), Union 2.1 and NVSS-ISW, are obtained as (-0.5808pm 0.025) for (Lambda)CDM, (-0.61pm 0.15) for both WCDM and CPL models. Our best fit for the combined jerk parameter for the (Lambda)CDM model is (1pm 3.971e-07), for WCDM it is (1.054pm 0.141), and for the CPL model it is (1.0654pm 0.1345). Also, the combined transition redshift is obtained as (0.724pm 0.047) for the (Lambda)CDM model.

We construct a special class of four-dimensional axisymmetric stationary space-times whose Ricci scalar is constant but are not Einstein space-times. We find that this solution has a ring singularity. At the end, we discuss some numerical results for these space-times.

A space experiment aimed at specifying the law of the Sun’s gravity more precisely is discussed. An extended “standard flight” scheme with two gravity assist maneuvers (slingshots) of a space probe near Venus and Earth is suggested, where the slingshots serve as amplifiers of small deflections caused by a deviation of the gravity law from a chosen ansatz. The deviation of the probe’s trajectory from its classic (Newtonian) pattern is calculated in detail using the isotropic Eddington–Robertson metric for the Sun’s gravity field and the “patched conic approximation” method for description of each slingshot. The trajectory deviation in the two-slingshots scheme is roughly assessed, the results indicating a principal possibility to detect the ultraweak distinctive feature of relativistic gravity.