Gravitation and Cosmology最新文献_第2页

Black Hole Formation from Collapsing Quark Binding String Fluid in (boldsymbol{f(R,T)}) Theory 夸克束缚弦流体在(boldsymbol{f(R,T)})中坍缩产生的黑洞形成理论

IF 1.2 4区物理与天体物理

Gravitation and Cosmology Pub Date : 2024-11-22 DOI: 10.1134/S0202289324700336

Umber Sheikh, Nida Ramzan, Yousra Aziz, Richard Pincak

{"title":"Black Hole Formation from Collapsing Quark Binding String Fluid in (boldsymbol{f(R,T)}) Theory","authors":"Umber Sheikh, Nida Ramzan, Yousra Aziz, Richard Pincak","doi":"10.1134/S0202289324700336","DOIUrl":"10.1134/S0202289324700336","url":null,"abstract":"We consider the gravitational collapse of a quark binding string fluid in (f(R,T)) theory of gravity. A quark binding string state of a fluid is expected to occur as a combination of quark matter and strings in the initial phases of the Universe. Assuming the collapse of this quark fluid, the junction conditions are derived, taking famous FRW and Schwarzschild space-times as the interior and exterior regions, respectively. We have assumed that (f(R,T)=alpha R+beta T), ((alpha), (beta) are positive constants). The collapsing gravitational mass is calculated under the conditions of a trace of the energy momentum tensor and a constant scalar curvature. It is calculated how long and how far the apparent horizons form. The constant term (f(R_{0},T_{0})) is a factor which delays the collapse. The event horizon formation is followed by creation of an apparent horizon, which results in a black hole. Additionally, the existence of the string tension lengthens the period before the horizon forms. As a result, it is anticipated that the Universe’s black holes are expected to originate during the quark binding string phase.","PeriodicalId":583,"journal":{"name":"Gravitation and Cosmology","volume":"30 4","pages":"441 - 449"},"PeriodicalIF":1.2,"publicationDate":"2024-11-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142691935","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

Wormholes in Rastall Gravity and Nonvacuum Space-Time 拉斯塔尔引力和非真空时空中的虫洞

IF 1.2 4区物理与天体物理

Gravitation and Cosmology Pub Date : 2024-11-22 DOI: 10.1134/S0202289324700397

Ayan Banerjee, Safiqul Islam, Archana Dixit, Anirudh Pradhan

引用次数: 0

Logamediate Inflation on the Swiss-Cheese Brane with Varying Cosmological Constant 瑞士奶酪链上的对数膨胀与变化的宇宙常数

IF 1.2 4区物理与天体物理

Gravitation and Cosmology Pub Date : 2024-11-22 DOI: 10.1134/S0202289324700415

Nasr Ahmed, Anirudh Pradhan

{"title":"Logamediate Inflation on the Swiss-Cheese Brane with Varying Cosmological Constant","authors":"Nasr Ahmed, Anirudh Pradhan","doi":"10.1134/S0202289324700415","DOIUrl":"10.1134/S0202289324700415","url":null,"abstract":"The existence of Schwarzschild black holes in the structure of a Swiss-cheese brane world has led to the conclusion that this specific brane-world scenario is more realistic than the FLRW branes. In this paper, we show that Logamediate inflation on the Swiss-cheese brane with a time-dependent cosmological constant (Lambda(H)) leads to a positive kinetic term and a negative potential with AdS minimum. The cosmic pressure (p) is always positive, but the energy density (rho) starts to get negative after finite time. However, there is a time interval where they both are positive. Although this behavior of (rho) can be considered as a drawback of the Swiss-cheese brane, where positive energy dominates the present universe, it has been suggested that the presence of some source of negative energy could have played a significant role in the early cosmic expansion. The model suffers from the eternal inflation problem which appears from the evolution of the first slow-roll parameter (epsilon). Due to the existence of the (rho^{2}) term, we have tested the new nonlinear energy conditions. The slow-roll parameters have been investigated and compared to Planck 15 results.","PeriodicalId":583,"journal":{"name":"Gravitation and Cosmology","volume":"30 4","pages":"523 - 535"},"PeriodicalIF":1.2,"publicationDate":"2024-11-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142691918","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

Causes of Energy Density Inhomogeneity in Energy Momentum Squared Gravity 能量动量平方引力中能量密度不均匀的原因

IF 1.2 4区物理与天体物理

Gravitation and Cosmology Pub Date : 2024-08-23 DOI: 10.1134/S0202289324700269

Z. Yousaf, M. Z. Bhatti, A. Farhat

{"title":"Causes of Energy Density Inhomogeneity in Energy Momentum Squared Gravity","authors":"Z. Yousaf, M. Z. Bhatti, A. Farhat","doi":"10.1134/S0202289324700269","DOIUrl":"10.1134/S0202289324700269","url":null,"abstract":"In the presence of an anisotropic fluid, we examine the irregularity factors for a spherically symmetric relativistic matter. In (f(mathcal{G},T^{2})) gravity, we investigate the equations of motion and dynamical relations using a systematic construction, where (T) stands for the trace of the energy-momentum tensor, and (mathcal{G}) is the Gauss–Bonnet term. With the use of the Weyl tensor, we examine two well-known differential equations that would lead to an analysis of the sources of inhomogeneities. In (f(mathcal{G},T^{2})) gravity, the irregularity factors are investigated by taking specific cases in the adiabatic and non-adiabatic regimes. We find that the conformal tensor and additional curvature terms compromise inhomogeneity for a pressureless nonradiating fluid and an isotropic fluid. In contrast to other cases, for a nonradiating anisotropic fluid, we observe that the term ((Pi+mathcal{E})) now accounts for the survival of density inhomogeneity, rather than just the Weyl tensor and the modified terms. The last case clearly illustrates how several components, namely, radiating terms, the fluid shear and the expansion scalar in the (f(mathcal{G},T^{2})) framework, are accountable for the formation of inhomogeneities from a homogeneous state of the structure. In the case (f(mathcal{G},T^{2})=0), all our results reduce to those of GR.","PeriodicalId":583,"journal":{"name":"Gravitation and Cosmology","volume":"30 3","pages":"353 - 367"},"PeriodicalIF":1.2,"publicationDate":"2024-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142209696","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

Effects of a Flux Field on Quantum Dynamics of Scalar Particles in Wormhole Background with Disclinations 通量场对带偏角虫洞背景中标量粒子量子动力学的影响

IF 1.2 4区物理与天体物理

Gravitation and Cosmology Pub Date : 2024-08-23 DOI: 10.1134/S0202289324700270

Faizuddin Ahmed, Abdelmalek Bouzenada

引用次数: 0

Machian Effects Inside a Rotating Spherical Shell 旋转球壳内的马赫效应

IF 1.2 4区物理与天体物理

Gravitation and Cosmology Pub Date : 2024-08-23 DOI: 10.1134/S0202289324700208

Elmo Benedetto, Luca D’Errico, Antonio Feoli

引用次数: 0

Interacting Bianchi Type-V Universe: Observational Constraints 相互作用的比安奇V型宇宙：观测约束

IF 1.2 4区物理与天体物理

Gravitation and Cosmology Pub Date : 2024-08-23 DOI: 10.1134/S0202289324700282

Archana Dixit, Anirudh Pradhan, K. Ghaderi

引用次数: 0

Riemann Solitons on Relativistic Space-Times 相对论时空的黎曼孤子

IF 1.2 4区物理与天体物理

Gravitation and Cosmology Pub Date : 2024-08-23 DOI: 10.1134/S020228932470021X

Shahroud Azami, Mehdi Jafari

引用次数: 0

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}

引用次数: 0

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

引用次数: 0