Gravitation and Cosmology最新文献

{"title":"Cosmological Models Based on an Asymmetric Scalar Doublet with Kinetic Coupling of Components. I. General Properties of the Cosmological Model","authors":"Yu. G. Ignat’ev,&nbsp;I. A. Kokh","doi":"10.1134/S0202289324700312","DOIUrl":"10.1134/S0202289324700312","url":null,"abstract":"<p>A mathematical model of the evolution of the Universe, based on an asymmetric doublet of classical and phantom scalar Higgs fields with a kinetic connection between the components, is constructed and studied. A detailed qualitative analysis is carried out, the properties of the modelCs symmetry and invariance with respect to the similarity transformation of fundamental constants are proven. The principles of numerical modeling are formulated, and an example of numerical modeling of the model evolution is given for a specific set of fundamental constants and initial conditions. The asymptotic behavior of the model near cosmological singularities is studied, and It is shown that it then manifests itself as a perfect fluid with an extremely rigid equation of state.</p>","PeriodicalId":583,"journal":{"name":"Gravitation and Cosmology","volume":"30 4","pages":"408 - 425"},"PeriodicalIF":1.2,"publicationDate":"2024-11-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142691934","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}

{"title":"Observational Constraints on Anisotropic Cosmology Through the Deceleration Parameter in Saez–Ballester Theory","authors":"Kangujam Priyokumar Singh,&nbsp;Asem Jotin Meitei","doi":"10.1134/S0202289324700403","DOIUrl":"10.1134/S0202289324700403","url":null,"abstract":"<p>We explore the cosmological tests of the deceleration parameter <span>(q=K-gamma/H)</span>, where <span>(K)</span> and <span>(gamma)</span> are arbitrary constants in a Bianchi type-III cosmological model in the framework of the Saez–Ballester theory of gravitation. Under the assumption that the shear scalar (<span>(sigma)</span>) is proportional to the expansion scalar (<span>(theta)</span>), we evaluate the physical and kinematic parameters, the jerk parameter, and the deceleration parameter (DP) in the early deceleration phase <span>((q&gt;0))</span> and the current acceleration phase <span>((q&lt;0))</span>. The energy conditions and the <span>(Om(z))</span> analysis for our spatially homogeneous and anisotropic Bianchi type-III model are discussed in details. Furthermore, we perform a <span>(chi^{2})</span> test to obtain the best fit values of the model parameters in the derived model by using <span>(46,H(z))</span> data sets in the redshift range <span>(0leq zleq 2.36)</span> and also analyze the present age of the universe.</p>","PeriodicalId":583,"journal":{"name":"Gravitation and Cosmology","volume":"30 4","pages":"507 - 522"},"PeriodicalIF":1.2,"publicationDate":"2024-11-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142691926","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}

{"title":"General Vacuum Solution of Modified Gravity with Gauss–Bonnet Term","authors":"M. V. Shubina","doi":"10.1134/S020228932470035X","DOIUrl":"10.1134/S020228932470035X","url":null,"abstract":"<p>We present a general vacuum solution of the modified Gauss–Bonnet gravity equations for the Friedmann–Lemaître–Robertson–Walker metric. We use an ansatz to reduce the gravitational equations to an ordinary differential equation for the function <span>(F=F(G))</span>. The solution obtained depends on an arbitrary function and is new. As an example, we take the arbitrary function in the form of a power one and analyze the solutions for both <span>(F(G))</span> and the main cosmological physical quantities as the scale factor, Hubble rate, the Gauss–Bonnet term and the scalar curvature.</p>","PeriodicalId":583,"journal":{"name":"Gravitation and Cosmology","volume":"30 4","pages":"455 - 461"},"PeriodicalIF":1.2,"publicationDate":"2024-11-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142691929","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}

{"title":"Tunneling of Hawking Radiation in Starobinsky–Bel–Robinson Gravity","authors":"Dhanvarsh Annamalai,&nbsp;Akshat Pandey","doi":"10.1134/S0202289324700348","DOIUrl":"10.1134/S0202289324700348","url":null,"abstract":"<p>We examine the Hawking radiation of a Schwarszchild-type black hole in Starobinsky–Bel–Robinson (SBR) gravity and calculate the corrected Hawking temperature using the tunneling method. We then discuss the deviation of our Hawking temperature from the standard Schwarszchild result. We relate the corrections to the Hawking temperature beyond the semiclassical approximation. We highlight that starting with a modification of the classical black hole geometry and calculating the semiclassical Hawking temperature yields temperature corrections comparable to those obtained when the classical background is kept unchanged and beyond-semiclassical terms in the temperature are included.</p>","PeriodicalId":583,"journal":{"name":"Gravitation and Cosmology","volume":"30 4","pages":"450 - 454"},"PeriodicalIF":1.2,"publicationDate":"2024-11-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142691933","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}

{"title":"Cosmological Models Based on an Asymmetric Scalar Doublet with Kinetic Coupling of Components. II. Numerical Modeling","authors":"Yu. G. Ignat’ev,&nbsp;I. A. Kokh","doi":"10.1134/S0202289324700324","DOIUrl":"10.1134/S0202289324700324","url":null,"abstract":"<p>Numerical modeling of a mathematical model of the cosmological evolution of an asymmetric scalar doublet with kinetic interaction between the components was carried out. A wide range of values of fundamental parameters and initial conditions of the model are considered. Various types of behavior have been identified: models with an infinite inflationary past and future—with and without a rebound point, models with a finite past and infinite future, with an infinite past and finite future (Big Rip), as well as models with a finite past and future. Based on numerical analysis, the behavior of models near the initial singularity and the Big Rip is studied; it is shown that in both cases the barotropic coefficient tends to unity, which corresponds to an extremely rigid state of matter near the singularities. A numerical example of the cosmological generation of the classical component of a scalar doublet by its phantom component is given. An assessment was made of the creation of the velocity of fermion pairs by a scalar field near the rebound points, and it has been shown that a scalar field at the cold stage of the Universe can ensure creation of the required number of massive scalarly charged fermions.</p>","PeriodicalId":583,"journal":{"name":"Gravitation and Cosmology","volume":"30 4","pages":"426 - 440"},"PeriodicalIF":1.2,"publicationDate":"2024-11-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142691930","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}

{"title":"New Path Equations in Einstein Non-Symmetric Geometry","authors":"M. I. Wanas,&nbsp;Samah Nabil,&nbsp;Kyrillos ElAbd,&nbsp;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}

{"title":"Dynamical System Analysis of Scalar Field Cosmology in (boldsymbol{f(Q,T)}) Gravity with (boldsymbol{q(z)}) Parametrization","authors":"Amit Samaddar,&nbsp;S. Surendra Singh,&nbsp;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}

{"title":"Black Hole Formation from Collapsing Quark Binding String Fluid in (boldsymbol{f(R,T)}) Theory","authors":"Umber Sheikh,&nbsp;Nida Ramzan,&nbsp;Yousra Aziz,&nbsp;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}

{"title":"Wormholes in Rastall Gravity and Nonvacuum Space-Time","authors":"Ayan Banerjee,&nbsp;Safiqul Islam,&nbsp;Archana Dixit,&nbsp;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}

{"title":"Logamediate Inflation on the Swiss-Cheese Brane with Varying Cosmological Constant","authors":"Nasr Ahmed,&nbsp;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}