Gravitation and Cosmology最新文献

Gravitational quantum theory applied to the weak gravity regions of deep gravitational wells predicts that photon-particle interaction cross sections can vary significantly, depending on the eigenspectral composition of the particle’s wave function. These often-reduced cross sections can potentially enable the nature and origin of dark matter to be understood without recourse to new particles or new physics, and without compromising the observations from nucleosynthesis and the cosmic microwave background. The present work extends the calculations of the Einstein-(A) coefficients relevant to these photon interactions (previously carried out for (1/r) central point-mass (CPM) potentials) to potentials derived from Navarro–Frenk–White (NFW) radial density profiles, which more realistically describe galaxy halos. The Wentzel–Kramers–Brillouin (WKB) and Modified Airy Function (MAF) approximation strategies were used to find the eigenfunctions appropriate to these potentials, and hence obtain the relevant Einstein-(A) coefficients. The results show that states with high principal and angular quantum number in NFW potentials have a significantly low transition rate. The results are also compared to those in the CPM potentials published in an earlier work.

The current study investigates dark energy cosmological models using a boundary term and a non-coincident gauge formulation of nonmetricity gravity. To obtain the modified field equations from the action, we considered the function (f(Q,C)=Q+lambda C^{m}), where (Q) is the nonmetricity scalar, (C) is the boundary term given by (C=mathring{R}-Q), and (lambda,m) are model parameters. The scale factor that we acquired, (a(t)=[sinh(k_{0}t)]^{1/n}), is determined by taking into account the time-dependent deceleration parameter. The constants (n) and (k_{0}) are used in this calculation. By comparing the Hubble function with (H(z)) datasets, we were able to use likelihood analysis to determine the model parameters that best fit the data. We have performed our result analysis and a discussion using the cosmological parameters, including the effective equation-of-state parameter, energy density, energy conditions, deceleration parameter, OM diagnostic analysis, and age of the universe, using these best match values of the model parameters.

We consider the time-symmetric initial data problem for GR minimally coupled to a phantom scalar field and a Maxwell field. The main focus is on initial data sets describing two interacting mouths of the same traversable wormhole. These data sets are similar in many respects to the Misner initial data with two black holes. More precisely, the corresponding solutions of the constraint equations determine the initial geometries which are topologically equivalent to the manifold (mathbb{S}^{2}timesmathbb{S}^{1})-{point} (i.e., ({mathbb{R}^{3}}) with a “handle”) and therefore describe initial states of intra-universe wormholes. Thus the results of the paper can be considered as an input for numerical simulation of such wormholes.

Following Einstein’s idea of representing particles as solitons, i.e., clots of some nonlinear universal field, the Brioschi 16-spinors are introduced since they prove to be well suited for the role of this fundamental field. Taking into account the principle of spontaneous symmetry breaking as the foundation for the stability of particles as topological solitons, the 16-spinor realization of the Skyrme–Faddeev chiral model is suggested. Within the scope of this model, it is possible to describe photons as solitons, the interaction with electromagnetic and gravitational fields being included. The existence of asymptotically exact soliton solutions to the equations of motion is proven, with the special large parameter (tau) being introduced.

In the context of the self-creation theory of gravitation and its counterpart, the relativity theory, we examine their associated Bianchi-type (VI_{0}) cosmological models by considering the existence of electromagnetic fields. The solution of the Einstein equations is presented by assuming that the cosmological model leads to a constant deceleration parameter ((q=textrm{const})). There is no restriction on the pressure and density for the solution derived (i.e., the equation of state is not used). The technique of obtaining the scalar field (phi) is different from that used in the previous investigation. A law that shows the effect of the electromagnetic field on the entropy of the universe is derived. The entropy introduced in the two theories is a consequence of the second law of thermodynamics. Consequently, the well-known thermodynamic functions of the universe are revisited. The scalar field introduced in the self-creation theory give a good explanation for the entropy and other thermodynamics functions of the universe as compared to general relativity. Moreover, in the absence of the electromagnetic field, the solution obtained in the self-creation theory and in general relativity indicate a radiation model, provided that the obtained models, whether expressed geometrically or physically are displayed.

We study the thermodynamics of black holes (BHs) with a Gauss–Bonnet correction term in ((3+1))-dimensional AdS space-time. It is known that this term has no effect on the equations of motion, however, it modifies the entropy which is calculated using Wald’s formula. The corrections to the area law appear in the form of a term involving the Gauss–Bonnet parameter. We study charged BHs, namely, Reissner-Nordström and Born–Infeld, under this regime. The first thing we encounter are divergences in heat capacity. After eliminating the possibility of first-order phase transition, we apply two well trusted methods from standard thermodynamics, namely, the Ehrenfest scheme and the Ruppeiner state space geometry analysis to ensure the second-order nature of the phase transition points. Our main focus in this study is on the effects of the Gauss–Bonnet and Born–Infeld parameters on the phase transition points.

We have explored the observed matter-antimatter asymmetry in the Universe to constrain the model parameters in Extended Symmetric Teleparallel Gravity (STG) or (f(Q,T)) gravity, where (Q) is the nonmetricity and (T) is the trace of the energy momentum tensor. We have considered two functional forms of (f(Q,T)) to find the baryon asymmetry to entropy ratio calculated at a decoupling temperature. Two different data sets, namely, the Hubble data set and the (text{Hubble}+text{BAO}+text{Pantheon}) data set, are used to constrain the scale factor, and the constrained model is used to obtain the baryon asymmetry to entropy ratio. It is observed that the model constrained from the Hubble data set favors a narrow range of the (f(Q,T)) gravity parameters to reproduce the observed baryon asymmetry.

Against the background of insufficient information on the law of gravity in near space, a justification is proposed for conducting a high-precision artificial experiment to determine the law of gravity dominating the Solar System. It is proposed to use the Sun–Earth–Venus system, space probes, and observers as a “gravitational space laboratory.” The scheme of a “standard ballistic flight” is defined as a complex trajectory of the probe, comprising the Earth-Venus path, accelerating gravitational maneuver at Venus, and the Venus–Earth orbit path. The data at the end point of the trajectory provide a conclusion on the format of the law of gravity of the Sun. The key instruments of the experiment, the gravity assist maneuver and the function of its sensitivity to changes in the probe–planet impact parameter, are described in detail. Schemes and results of an analytical calculation and numerical construction of the probe trajectory are given. It is shown that this experiment provides a margin for successful observation of the probe positions in classical and relativistic gravity, which makes it possible to distinguish the gravity type. At the evaluation level, the issues of economics of the experiment are touched upon, and the provision of observational statistics and the possibility of obtaining additional scientific and practically significant information are discussed.

We study the dependence of the parameters of the evolution of scalarly charged black holes (BHs) in the early Universe on the parameters of field theories of interaction, and the influence of the geometric structure of the relative position of BHs on the limitation of their maximum mass, The problem of the metric of a scalarly charged BH in a medium of expanding scalarly charged matter is discussed, the expression is obtained for the macroscopic cosmological constant at late stages of expansion, generated by quadratic fluctuations of the metric, connecting the cosmological constant value with the BH masses and their concentration.

We investigate an exact Universe model which is observationally viable and filled with a binary mixture of a perfect fluid and the cosmological constant (Lambda). We consider the redshift drift (dot{z}=(1+z)H_{0}-H(z)) and perform statistical tests to obtain the best fit value of the model parameters of the derived Universe with its observed values. Here, (H_{0}) and (z) denote the present value of the Hubble constant and the redshift, respectively. We estimate the best fit values of the Hubble constant and the density parameters as (H_{0}=68.58pm 0.84) km/(s Mpc), ((Omega_{m})_{0}=0.26pm 0.010), and ((Omega_{Lambda})_{0}=0.71pm 0.025) by bounding the derived model with the latest observational Hubble data (OHD), while with joint Pantheon data and OHD, its values are (H_{0}=71.93pm 0.58) km/(s Mpc), ((Omega_{m})_{0}=0.272pm 0.06), and ((Omega_{Lambda})_{0}=0.74pm 0.09). The analysis of the deceleration and jerk parameters shows that the Universe in the derived model is compatible with the (Lambda)CDM model. We also investigate that the cosmological models owning a redshift drift minimize the (H_{0}) tension.