Pub Date : 2024-11-22DOI: 10.1134/S0202289324700385
M. I. Wanas, Samah Nabil, Kyrillos ElAbd, Nouran E. Abdelhamid
Adopting Bażański’s action, two new classes of path equations are derived in Einstein’s nonsymmetric geometry. The first class is the path equations of a test particle moving in a gravitational field, while the second class represents path equations of charged particles. The quantum features of this geometry appear in both classes. The path equations of charged particles give rise to the Lorentz force. Moreover, these path equations may represent an interpretation of some interactions between torsion and the electromagnetic potential even if the electromagnetic force vanishes. It is to be noted that the above two classes of paths are formulated in terms of Einstein’s n onsymmetric connection. An explicit formula of such a connection, satisfying the Einstein metricity condition, is obtained by localizing the global formula given recently by Ivanov and Zlatanović.
采用巴扎斯基的作用,在爱因斯坦的非对称几何中导出了两类新的路径方程。第一类是测试粒子在引力场中运动的路径方程,第二类是带电粒子的路径方程。这两类几何的量子特征都会出现。带电粒子的路径方程产生了洛伦兹力。此外,即使电磁力消失,这些路径方程也可以解释扭转与电磁势之间的某些相互作用。需要指出的是,上述两类路径是根据爱因斯坦的 n 对称连接来表述的。通过将伊万诺夫和兹拉塔诺维奇最近给出的全局公式本地化,可以得到满足爱因斯坦度量条件的这种连接的明确公式。
{"title":"New Path Equations in Einstein Non-Symmetric Geometry","authors":"M. I. Wanas, Samah Nabil, Kyrillos ElAbd, Nouran E. Abdelhamid","doi":"10.1134/S0202289324700385","DOIUrl":"10.1134/S0202289324700385","url":null,"abstract":"<p>Adopting Bażański’s action, two new classes of path equations are derived in Einstein’s nonsymmetric geometry. The first class is the path equations of a test particle moving in a gravitational field, while the second class represents path equations of charged particles. The quantum features of this geometry appear in both classes. The path equations of charged particles give rise to the Lorentz force. Moreover, these path equations may represent an interpretation of some interactions between torsion and the electromagnetic potential even if the electromagnetic force vanishes. It is to be noted that the above two classes of paths are formulated in terms of Einstein’s n onsymmetric connection. An explicit formula of such a connection, satisfying the Einstein metricity condition, is obtained by localizing the global formula given recently by Ivanov and Zlatanović.</p>","PeriodicalId":583,"journal":{"name":"Gravitation and Cosmology","volume":"30 4","pages":"489 - 495"},"PeriodicalIF":1.2,"publicationDate":"2024-11-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142691932","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}
Pub Date : 2024-11-22DOI: 10.1134/S0202289324700361
Amit Samaddar, S. Surendra Singh, Md Khurshid Alam
We explore the cosmological characteristics of the function of (f(Q,T)=alpha Q+betasqrt{Q}+gamma T) where (alpha), (beta) and (gamma) are constants. This investigation is conducted by considering the deceleration parameter in the form (q(z)=q_{0}+q_{1}dfrac{z(1+z)}{1+z^{2}}), where (q_{0}) and (q_{1}) are constants. We apply combined Hubble (46) and BAO (15) data sets to determine the present value of the cosmological parameters. At the (1-sigma) and (2-sigma) confidence levels, we obtain the value of (q_{0}=-0.373^{+0.072}_{-0.070}). Additionally, the plot of (q) vs. (z) shows the accelerated stage of the Universe. We compute (H(z)) using the given form of (q(z)). We examine the behavior of all physical parameters using the expression for (H(z)). We also analyze the statefinder pairs ({r,s}) and plot the (r-s) and (r{-}q) planes. They describe the (Lambda)CDM period for our model. Once more, we investigate the (Om(z)) parameter and the sound speed in this study. The Universe is in a phantom epoch and remains stable. We also employ dynamical systems in our model, considering two distinct forms of the scalar potential. We identify the equilibrium points for both models. For Model 1, three stable equilibrium points are identified, while for Model 2, two stable points are determined. The phase diagram elucidates stability criteria of the equilibrium points. We explore the parameters (Omega_{phi}), (q), (omega_{phi}) and (omega_{textrm{eff}}) at each equilibrium point. The characteristic values of both models are investigated. Based on all calculations, we conclude that our model is stable and consistent with all observational data indicating that the Universe is in a phase of accelerated expansion.
{"title":"Dynamical System Analysis of Scalar Field Cosmology in (boldsymbol{f(Q,T)}) Gravity with (boldsymbol{q(z)}) Parametrization","authors":"Amit Samaddar, S. Surendra Singh, Md Khurshid Alam","doi":"10.1134/S0202289324700361","DOIUrl":"10.1134/S0202289324700361","url":null,"abstract":"<p>We explore the cosmological characteristics of the function of <span>(f(Q,T)=alpha Q+betasqrt{Q}+gamma T)</span> where <span>(alpha)</span>, <span>(beta)</span> and <span>(gamma)</span> are constants. This investigation is conducted by considering the deceleration parameter in the form <span>(q(z)=q_{0}+q_{1}dfrac{z(1+z)}{1+z^{2}})</span>, where <span>(q_{0})</span> and <span>(q_{1})</span> are constants. We apply combined Hubble <span>(46)</span> and BAO <span>(15)</span> data sets to determine the present value of the cosmological parameters. At the <span>(1-sigma)</span> and <span>(2-sigma)</span> confidence levels, we obtain the value of <span>(q_{0}=-0.373^{+0.072}_{-0.070})</span>. Additionally, the plot of <span>(q)</span> vs. <span>(z)</span> shows the accelerated stage of the Universe. We compute <span>(H(z))</span> using the given form of <span>(q(z))</span>. We examine the behavior of all physical parameters using the expression for <span>(H(z))</span>. We also analyze the statefinder pairs <span>({r,s})</span> and plot the <span>(r-s)</span> and <span>(r{-}q)</span> planes. They describe the <span>(Lambda)</span>CDM period for our model. Once more, we investigate the <span>(Om(z))</span> parameter and the sound speed in this study. The Universe is in a phantom epoch and remains stable. We also employ dynamical systems in our model, considering two distinct forms of the scalar potential. We identify the equilibrium points for both models. For Model 1, three stable equilibrium points are identified, while for Model 2, two stable points are determined. The phase diagram elucidates stability criteria of the equilibrium points. We explore the parameters <span>(Omega_{phi})</span>, <span>(q)</span>, <span>(omega_{phi})</span> and <span>(omega_{textrm{eff}})</span> at each equilibrium point. The characteristic values of both models are investigated. Based on all calculations, we conclude that our model is stable and consistent with all observational data indicating that the Universe is in a phase of accelerated expansion.</p>","PeriodicalId":583,"journal":{"name":"Gravitation and Cosmology","volume":"30 4","pages":"462 - 480"},"PeriodicalIF":1.2,"publicationDate":"2024-11-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142691917","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}
Pub Date : 2024-11-22DOI: 10.1134/S0202289324700336
Umber Sheikh, Nida Ramzan, Yousra Aziz, Richard Pincak
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.
{"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":"<p>We consider the gravitational collapse of a quark binding string fluid in <span>(f(R,T))</span> 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 <span>(f(R,T)=alpha R+beta T)</span>, (<span>(alpha)</span>, <span>(beta)</span> 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 <span>(f(R_{0},T_{0}))</span> 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.</p>","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}
We present a family of static and spherically symmetric wormholes in Rastall gravity. A unique characteristic of this modified theory is violation of the local conservation of the energy-momentum tensor. These wormholes are supported by applying a specific equation of state for matter satisfying the tracelessness constraint [Kar and Sahdev: Phys. Rev D 52, 2030 (1995)]. Next, we impose some restrictions on the redshift function and solve the field equations analytically for a classical traversable wormholes. Finally, we investigate some issues concerning the energy conditions and the volume integral quantifier in these time-interdependent geometries.
我们提出了拉斯塔尔引力中的静态球对称虫洞系列。这种修正理论的一个独特特征是违反了能量-动量张量的局部守恒。这些虫洞是通过对满足无迹约束的物质应用特定的状态方程来支持的[Kar 和 Sahdev:Phys. Rev D 52, 2030 (1995)]。接下来,我们对红移函数施加了一些限制,并对经典可穿越虫洞的场方程进行了分析求解。最后,我们研究了这些时间相关几何中有关能量条件和体积积分量子的一些问题。
{"title":"Wormholes in Rastall Gravity and Nonvacuum Space-Time","authors":"Ayan Banerjee, Safiqul Islam, Archana Dixit, Anirudh Pradhan","doi":"10.1134/S0202289324700397","DOIUrl":"10.1134/S0202289324700397","url":null,"abstract":"<p>We present a family of static and spherically symmetric wormholes in Rastall gravity. A unique characteristic of this modified theory is violation of the local conservation of the energy-momentum tensor. These wormholes are supported by applying a specific equation of state for matter satisfying the tracelessness constraint [Kar and Sahdev: Phys. Rev D <b>52</b>, 2030 (1995)]. Next, we impose some restrictions on the redshift function and solve the field equations analytically for a classical traversable wormholes. Finally, we investigate some issues concerning the energy conditions and the volume integral quantifier in these time-interdependent geometries.</p>","PeriodicalId":583,"journal":{"name":"Gravitation and Cosmology","volume":"30 4","pages":"496 - 506"},"PeriodicalIF":1.2,"publicationDate":"2024-11-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142691897","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}
Pub Date : 2024-11-22DOI: 10.1134/S0202289324700415
Nasr Ahmed, Anirudh Pradhan
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.
{"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":"<p>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 <span>(Lambda(H))</span> leads to a positive kinetic term and a negative potential with AdS minimum. The cosmic pressure <span>(p)</span> is always positive, but the energy density <span>(rho)</span> starts to get negative after finite time. However, there is a time interval where they both are positive. Although this behavior of <span>(rho)</span> 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 <span>(epsilon)</span>. Due to the existence of the <span>(rho^{2})</span> term, we have tested the new nonlinear energy conditions. The slow-roll parameters have been investigated and compared to Planck 15 results.</p>","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}
Pub Date : 2024-08-23DOI: 10.1134/S0202289324700269
Z. Yousaf, M. Z. Bhatti, A. Farhat
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.
摘要 在存在各向异性流体的情况下,我们研究了球对称相对论物质的不规则系数。在(f(mathcal{G},T^{2}))引力中,我们使用系统结构研究了运动方程和动力学关系,其中(T)代表能动张量的迹,(mathcal{G})是高斯-波奈项。利用韦尔张量,我们研究了两个众所周知的微分方程,它们将导致对不均匀性来源的分析。在(f(mathcal{G},T^{2}))引力中,我们通过绝热和非绝热状态下的具体案例研究了不规则因子。我们发现,对于无压非辐射流体和各向同性流体,共形张量和附加曲率项会影响不均匀性。与其他情况不同的是,对于非辐射各向异性流体,我们观察到项((Pi+mathcal{E}))现在解释了密度不均匀性的存续,而不仅仅是韦尔张量和修正项。最后一种情况清楚地说明了在(f(mathcal{G},T^{2}))框架中,辐射项、流体剪切力和膨胀标量这几个部分是如何从结构的均质状态形成不均匀性的。在 (f(mathcal{G},T^{2})=0) 的情况下,我们的所有结果都与 GR 的结果一致。
{"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":"<p>In the presence of an anisotropic fluid, we examine the irregularity factors for a spherically symmetric relativistic matter. In <span>(f(mathcal{G},T^{2}))</span> gravity, we investigate the equations of motion and dynamical relations using a systematic construction, where <span>(T)</span> stands for the trace of the energy-momentum tensor, and <span>(mathcal{G})</span> 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 <span>(f(mathcal{G},T^{2}))</span> 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 <span>((Pi+mathcal{E}))</span> 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 <span>(f(mathcal{G},T^{2}))</span> framework, are accountable for the formation of inhomogeneities from a homogeneous state of the structure. In the case <span>(f(mathcal{G},T^{2})=0)</span>, all our results reduce to those of GR.</p>","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}
Pub Date : 2024-08-23DOI: 10.1134/S0202289324700270
Faizuddin Ahmed, Abdelmalek Bouzenada
In this research, we focus on investigating the behavior of zero-spin scalar boson-antiboson particles in a specific space-time of ((1+2))-dimensional circularly symmetric and static traversable wormhole with cosmic strings, all under the influence of a quantum flux field. We start by deriving the wave equation from the Klein–Gordon equation, which governs the relativistic quantum motion of scalar bosons-antibosons. By solving this equation using the confluent Heun equation, we obtain the ground state energy level (E^{+}_{1,ell}) and the corresponding wave function (Psi^{+}_{1,ell}) as a particular case. The main findings of this study indicate that various factors, such as the presence of cosmic strings, the radius of the wormhole throat, and the quantum flux, have significant impacts on the behavior of scalar bosons-antibosons.
{"title":"Effects of a Flux Field on Quantum Dynamics of Scalar Particles in Wormhole Background with Disclinations","authors":"Faizuddin Ahmed, Abdelmalek Bouzenada","doi":"10.1134/S0202289324700270","DOIUrl":"10.1134/S0202289324700270","url":null,"abstract":"<p>In this research, we focus on investigating the behavior of zero-spin scalar boson-antiboson particles in a specific space-time of <span>((1+2))</span>-dimensional circularly symmetric and static traversable wormhole with cosmic strings, all under the influence of a quantum flux field. We start by deriving the wave equation from the Klein–Gordon equation, which governs the relativistic quantum motion of scalar bosons-antibosons. By solving this equation using the confluent Heun equation, we obtain the ground state energy level <span>(E^{+}_{1,ell})</span> and the corresponding wave function <span>(Psi^{+}_{1,ell})</span> as a particular case. The main findings of this study indicate that various factors, such as the presence of cosmic strings, the radius of the wormhole throat, and the quantum flux, have significant impacts on the behavior of scalar bosons-antibosons.</p>","PeriodicalId":583,"journal":{"name":"Gravitation and Cosmology","volume":"30 3","pages":"368 - 375"},"PeriodicalIF":1.2,"publicationDate":"2024-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142209711","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}
Pub Date : 2024-08-23DOI: 10.1134/S0202289324700208
Elmo Benedetto, Luca D’Errico, Antonio Feoli
During typical general relativity courses, the gravitational fields generated by rotating objects and the so-called frame dragging effect are explained by emphasizing the presence of a gravitational Coriolis-like force term. It is well known that, in a rotating system, there is also a fictitious centrifugal force. In general, textbooks do not discuss also the possibility of a gravitational centrifugal-like force, and, in a recent paper, we have analyzed the presence of a repulsive force in the vicinity of a rotating mass. Now, however, we want to reviews some historical aspects of Mach’s Principle and to analyze the centrifugal gravitational term inside a rotating spherical shell, with a new simple approach.
{"title":"Machian Effects Inside a Rotating Spherical Shell","authors":"Elmo Benedetto, Luca D’Errico, Antonio Feoli","doi":"10.1134/S0202289324700208","DOIUrl":"10.1134/S0202289324700208","url":null,"abstract":"<p>During typical general relativity courses, the gravitational fields generated by rotating objects and the so-called frame dragging effect are explained by emphasizing the presence of a gravitational Coriolis-like force term. It is well known that, in a rotating system, there is also a fictitious centrifugal force. In general, textbooks do not discuss also the possibility of a gravitational centrifugal-like force, and, in a recent paper, we have analyzed the presence of a repulsive force in the vicinity of a rotating mass. Now, however, we want to reviews some historical aspects of Mach’s Principle and to analyze the centrifugal gravitational term inside a rotating spherical shell, with a new simple approach.</p>","PeriodicalId":583,"journal":{"name":"Gravitation and Cosmology","volume":"30 3","pages":"301 - 305"},"PeriodicalIF":1.2,"publicationDate":"2024-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142209690","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}
Pub Date : 2024-08-23DOI: 10.1134/S0202289324700282
Archana Dixit, Anirudh Pradhan, K. Ghaderi
This investigation focuses on a Bianchi type-V universe characterized by spatial homogeneity and anisotropy, wherein the cosmic medium consists of interacting dark matter and holographic dark energy. We obtain solutions to the field equations by considering the Hubble parameter (H(z)=(H_{0}/sqrt{2})sqrt{1+(1+z)^{2n}}), and constrain the model parameters. Employing Bayesian analysis and likelihood functions in conjunction with the Markov Chain Monte Carlo (MCMC) method, we determine the following model parameters: (H_{0}=71.3388^{+0.00010}_{-0.00094}), and (n=-1.08147^{+0.00010}_{-0.00010}). In this study, we constrain the model parameters by using the joint datasets ((H(z)+textrm{BAO}+textrm{Pantheon})). We explain the physical and geometric aspects of the model. We also examine the behavior of the velocity of sound and different energy conditions to test the viability of our cosmological model.
摘要 本研究的重点是以空间均匀性和各向异性为特征的边奇型-V宇宙,其中宇宙介质由相互作用的暗物质和全息暗能量组成。我们通过考虑哈勃参数(H(z)=(H_{0}/sqrt{2})sqrt{1+(1+z)^{2n}}/)得到场方程的解,并对模型参数进行约束。利用贝叶斯分析和似然函数,结合马尔可夫链蒙特卡罗(MCMC)方法,我们确定了以下模型参数:(H_{0}=71.3388^{+0.00010}_{-0.00094}), and (n=-1.08147^{+0.00010}_{-0.00010}).在这项研究中,我们利用联合数据集((H(z)+textrm{BAO}+textrm{Pantheon})来约束模型参数。)我们解释了模型的物理和几何方面。我们还研究了声速的行为和不同的能量条件,以检验我们的宇宙学模型的可行性。
{"title":"Interacting Bianchi Type-V Universe: Observational Constraints","authors":"Archana Dixit, Anirudh Pradhan, K. Ghaderi","doi":"10.1134/S0202289324700282","DOIUrl":"10.1134/S0202289324700282","url":null,"abstract":"<p>This investigation focuses on a Bianchi type-V universe characterized by spatial homogeneity and anisotropy, wherein the cosmic medium consists of interacting dark matter and holographic dark energy. We obtain solutions to the field equations by considering the Hubble parameter <span>(H(z)=(H_{0}/sqrt{2})sqrt{1+(1+z)^{2n}})</span>, and constrain the model parameters. Employing Bayesian analysis and likelihood functions in conjunction with the Markov Chain Monte Carlo (MCMC) method, we determine the following model parameters: <span>(H_{0}=71.3388^{+0.00010}_{-0.00094})</span>, and <span>(n=-1.08147^{+0.00010}_{-0.00010})</span>. In this study, we constrain the model parameters by using the joint datasets (<span>(H(z)+textrm{BAO}+textrm{Pantheon})</span>). We explain the physical and geometric aspects of the model. We also examine the behavior of the velocity of sound and different energy conditions to test the viability of our cosmological model.</p>","PeriodicalId":583,"journal":{"name":"Gravitation and Cosmology","volume":"30 3","pages":"376 - 391"},"PeriodicalIF":1.2,"publicationDate":"2024-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142209712","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}
Pub Date : 2024-08-23DOI: 10.1134/S020228932470021X
Shahroud Azami, Mehdi Jafari
We examine almost Riemann solitons and almost gradient Riemann solitons in generalized Robertson–Walker space-times and perfect fluid space-times. At first, we prove that if a generalized Robertson–Walker space-time admits an almost Riemann soliton or an almost gradient Riemann soliton, then it becomes a perfect fluid space-time. Next, we observe that a space-time with an almost Riemann soliton whose potential vector field, is a conformal vector field, is an Einstein manifold, and if the potential vector field is a nonhomothetic conformal vector field, then space-time is of Petrov type O or N. In final, we prove that if a generalized Robertson–Walker space-time satisfies the definition of an almost Riemann soliton, and (Q.P=0) then it is an Einstein manifold, and consequently it is a perfect fluid space-time.
摘要 我们研究广义罗伯逊-沃克时空和完美流体时空中的近黎曼孤子和近梯度黎曼孤子。首先,我们证明,如果广义罗伯逊-沃克时空中存在几乎黎曼孤子或几乎梯度黎曼孤子,那么它就成为完美流体时空。接下来,我们观察到,一个具有几乎黎曼孤子的时空,如果其势能向量场是共形向量场,那么它就是爱因斯坦流形;如果势能向量场是非同调共形向量场,那么它就是彼得罗夫 O 或 N 型时空。最后,我们证明,如果广义罗伯逊-沃克时空满足几乎黎曼孤子的定义,并且(Q.P=0),那么它就是爱因斯坦流形,因此它是完美流体时空。
{"title":"Riemann Solitons on Relativistic Space-Times","authors":"Shahroud Azami, Mehdi Jafari","doi":"10.1134/S020228932470021X","DOIUrl":"10.1134/S020228932470021X","url":null,"abstract":"<p>We examine almost Riemann solitons and almost gradient Riemann solitons in generalized Robertson–Walker space-times and perfect fluid space-times. At first, we prove that if a generalized Robertson–Walker space-time admits an almost Riemann soliton or an almost gradient Riemann soliton, then it becomes a perfect fluid space-time. Next, we observe that a space-time with an almost Riemann soliton whose potential vector field, is a conformal vector field, is an Einstein manifold, and if the potential vector field is a nonhomothetic conformal vector field, then space-time is of Petrov type O or N. In final, we prove that if a generalized Robertson–Walker space-time satisfies the definition of an almost Riemann soliton, and <span>(Q.P=0)</span> then it is an Einstein manifold, and consequently it is a perfect fluid space-time.</p>","PeriodicalId":583,"journal":{"name":"Gravitation and Cosmology","volume":"30 3","pages":"306 - 311"},"PeriodicalIF":1.2,"publicationDate":"2024-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142209691","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}