Gravitation and Cosmology最新文献_第4页

On a Reconstruction Procedure for Special Spherically Symmetric Metrics in the Scalar-Einstein–Gauss–Bonnet Model: the Schwarzschild Metric Test 论标量-爱因斯坦-高斯-波内特模型中特殊球面对称度量的重构程序：施瓦兹柴尔德度量检验

IF 1.2 4区物理与天体物理

Gravitation and Cosmology Pub Date : 2024-08-23 DOI: 10.1134/S0202289324700257

K. K. Ernazarov, V. D. Ivashchuk

{"title":"On a Reconstruction Procedure for Special Spherically Symmetric Metrics in the Scalar-Einstein–Gauss–Bonnet Model: the Schwarzschild Metric Test","authors":"K. K. Ernazarov, V. D. Ivashchuk","doi":"10.1134/S0202289324700257","DOIUrl":"10.1134/S0202289324700257","url":null,"abstract":"The 4D gravitational model with a real scalar field (varphi), Einstein and Gauss–Bonnet terms is considered. The action contains the potential (U(varphi)) and the Gauss–Bonnet coupling function (f(varphi)). For a special static spherically symmetric metric (ds^{2}=(A(u))^{-1}du^{2}-A(u)dt^{2}+u^{2}dOmega^{2}), with (A(u)>0) ((u>0) is a radial coordinate), we verify the so-called reconstruction procedure suggested by Nojiri and Nashed. This procedure presents certain implicit relations for (U(varphi)) and (f(varphi)) which lead to exact solutions to the equations of motion for a given metric governed by (A(u)). We confirm that all relations in the approach of Nojiri and Nashed for (f(varphi(u))) and (varphi(u)) are correct, but the relation for (U(varphi(u))) contains a typo which is eliminated in this paper. Here we apply the procedure to the (external) Schwarzschild metric with the gravitational radius (2mu) and (u>2mu). Using the “no-ghost” restriction (i.e., reality of (varphi(u))), we find two families of ((U(varphi),f(varphi))). The first one gives us the Schwarzschild metric defined for (u>3mu), while the second one describes the Schwarzschild metric defined for (2mu<u<3mu) ((3mu) is the radius of the photon sphere). In both cases the potential (U(varphi)) is negative.","PeriodicalId":583,"journal":{"name":"Gravitation and Cosmology","volume":"30 3","pages":"344 - 352"},"PeriodicalIF":1.2,"publicationDate":"2024-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142209695","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

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Images of Black Holes Viewed by a Distant Observer 遥远观测者看到的黑洞图像

IF 1.2 4区物理与天体物理

Gravitation and Cosmology Pub Date : 2024-08-23 DOI: 10.1134/S0202289324700154

V. I. Dokuchaev

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A Regular Center Instead of a Black Bounce 常规中心而非黑色弹跳

IF 1.2 4区物理与天体物理

Gravitation and Cosmology Pub Date : 2024-08-23 DOI: 10.1134/S0202289324700178

S. V. Bolokhov, K. A. Bronnikov, M. V. Skvortsova

{"title":"A Regular Center Instead of a Black Bounce","authors":"S. V. Bolokhov, K. A. Bronnikov, M. V. Skvortsova","doi":"10.1134/S0202289324700178","DOIUrl":"10.1134/S0202289324700178","url":null,"abstract":"The widely discussed “black-bounce” mechanism of removing a singularity at (r=0) in a spherically symmetric space-time, proposed by Simpson and Visser, consists in removing the point (r=0) and its close neighborhood, resulting in emergence of a regular minimum of the spherical radius that can be a wormhole throat or a regular bounce. Instead, it has been recently proposed to make (r=0) a regular center by properly modifying the metric, still preserving its form in regions far from (r=0). Different algorithms of such modifications have been formulated for a few classes of singularities. The previous paper considered space-times whose Ricci tensor satisfies the condition (R^{t}_{t}=R^{r}_{r}), and regular modifications were obtained for the Schwarzschild, Reissner-Nordström metrics, and two examples of solutions with magnetic fields obeying nonlinear electrodynamics (NED). The present paper considers regular modifications of more general space-times, and as examples, modifications with a regular center have been obtained for the Fisher (also known as JNW) solution with a naked singularity and a family of dilatonic black holes. Possible field sources of the new regular metrics are considered in the framework of general relativity (GR), using the fact that any static, spherically symmetric metric can be presented as a solution with a combined source involving NED and a scalar field with some self-interaction potential. This scalar field is, in general, not required to be of phantom nature (unlike the sources for black bounces), but in the examples discussed here, the possible scalar sources are phantom in a close neighborhood of (r=0) and are canonical outside it.","PeriodicalId":583,"journal":{"name":"Gravitation and Cosmology","volume":"30 3","pages":"265 - 278"},"PeriodicalIF":1.2,"publicationDate":"2024-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142209854","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

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Ringing of Extreme Regular Black Holes 极端普通黑洞的振荡

IF 1.2 4区物理与天体物理

Gravitation and Cosmology Pub Date : 2024-08-23 DOI: 10.1134/S020228932470018X

Milena Skvortsova

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Prediction of Super-Exponentially Accelerated Universe in a Friedmann–Lemaitre–Robertson–Walker Metric 弗里德曼-勒梅特尔-罗伯逊-沃克公设中的超指数加速宇宙预测

IF 1.2 4区物理与天体物理

Gravitation and Cosmology Pub Date : 2024-08-23 DOI: 10.1134/S0202289324700221

Giridhari Deogharia, Sandip Dutta

{"title":"Prediction of Super-Exponentially Accelerated Universe in a Friedmann–Lemaitre–Robertson–Walker Metric","authors":"Giridhari Deogharia, Sandip Dutta","doi":"10.1134/S0202289324700221","DOIUrl":"10.1134/S0202289324700221","url":null,"abstract":"A coupled model of variable-modified Chaplygin gas (as a candidate of dark energy) and dark matter is assumed in the background of the Friedmann–Lemaitre–Robertson–Walker universe. Firstly, a two-dimensional autonomous dynamical system is considered for a flat universe after determining some suitable dimensionless parameters. The evolution of those parameters along with the deceleration parameter is observed. Next, the evolution of matter and energy density parameters is studied for variational coupling parameters. Phase portrait analysis is performed to explain the present as well as future expansion of the universe. Secondly, both three- and four-dimensional dynamic systems are constructed when the evolution of spatially homogeneous and isotropic model of the universe is considered, which includes the cosmological constant and three-curvature symmetry surfaces. For the three-dimensional system, updates of dimensionless parameters along with deceleration parameters are analyzed for variational coupling parameters with respect to progression of the universe. Again, the evolution of the deceleration parameter is studied for different values of (n). Stability analysis is carried out for the concerned dynamical system with the help of eigenvalues. The four-dimensional dynamical system is remarkable as it helps to study the evolution of (Lambda) density along with other parameters. Lastly, for the concerned dynamical system, the evolution of matter and energy density parameters is analyzed for different values of (c) to study whether or not the coupling parameters affect the ultimate evolution of the universe.","PeriodicalId":583,"journal":{"name":"Gravitation and Cosmology","volume":"30 3","pages":"312 - 322"},"PeriodicalIF":1.2,"publicationDate":"2024-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142209692","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Quantum Gravitational Eigenstates in Navarro–Frenk–White Potentials 纳瓦罗-弗伦克-怀特势中的量子引力特征状态

IF 1.2 4区物理与天体物理

Gravitation and Cosmology Pub Date : 2024-08-23 DOI: 10.1134/S0202289324700233

Isaac Lobo, Allan Ernest, Matthew Collins

{"title":"Quantum Gravitational Eigenstates in Navarro–Frenk–White Potentials","authors":"Isaac Lobo, Allan Ernest, Matthew Collins","doi":"10.1134/S0202289324700233","DOIUrl":"10.1134/S0202289324700233","url":null,"abstract":"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.","PeriodicalId":583,"journal":{"name":"Gravitation and Cosmology","volume":"30 3","pages":"323 - 329"},"PeriodicalIF":1.2,"publicationDate":"2024-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142209693","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Transit Cosmological Models in Non-Coincident Gauge Formulation of (boldsymbol{f(Q,C)}) Gravity Theory with Observational Constraints 具有观测约束条件的 $$boldsymbol{f(Q,C)}$ 重力理论的非共轭引力公式中的过境宇宙学模型

IF 1.2 4区物理与天体物理

Gravitation and Cosmology Pub Date : 2024-08-23 DOI: 10.1134/S0202289324700245

Dinesh Chandra Maurya

{"title":"Transit Cosmological Models in Non-Coincident Gauge Formulation of (boldsymbol{f(Q,C)}) Gravity Theory with Observational Constraints","authors":"Dinesh Chandra Maurya","doi":"10.1134/S0202289324700245","DOIUrl":"10.1134/S0202289324700245","url":null,"abstract":"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.","PeriodicalId":583,"journal":{"name":"Gravitation and Cosmology","volume":"30 3","pages":"330 - 343"},"PeriodicalIF":1.2,"publicationDate":"2024-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142209694","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

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Initial Data Problem for a Traversable Wormhole with Interacting Mouths 具有相互作用虫口的可穿越虫洞的初始数据问题

IF 1.2 4区物理与天体物理

Gravitation and Cosmology Pub Date : 2024-08-23 DOI: 10.1134/S0202289324700191

A. L. Smirnov

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Brioschi 16-Spinors and Photons as Solitons in the Skyrme—Faddeev Chiral Model 布里奥斯奇 16--Skyrme-Faddeev 手性模型中的孤子和光子

IF 1.2 4区物理与天体物理

Gravitation and Cosmology Pub Date : 2024-08-23 DOI: 10.1134/S0202289324700142

Yu. P. Rybakov

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Self-Creation Gravity Versus General Relativity: a Cosmological Comparison 自创引力与广义相对论：宇宙学比较

IF 1.2 4区物理与天体物理

Gravitation and Cosmology Pub Date : 2024-08-23 DOI: 10.1134/S0202289324700166

E. A. Hegazy, Magd E. Kahil

{"title":"Self-Creation Gravity Versus General Relativity: a Cosmological Comparison","authors":"E. A. Hegazy, Magd E. Kahil","doi":"10.1134/S0202289324700166","DOIUrl":"10.1134/S0202289324700166","url":null,"abstract":"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.","PeriodicalId":583,"journal":{"name":"Gravitation and Cosmology","volume":"30 3","pages":"254 - 264"},"PeriodicalIF":1.2,"publicationDate":"2024-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142226560","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0