General Relativity and Gravitation最新文献_第9页

Bianchi type IX cosmological model with perfect fluid in ({varvec{f}}({varvec{R}},{varvec{T}})) theory of gravity ({varvec{f}}({varvec{R}},{varvec{T}}))重力理论中具有完美流体的Bianchi IX型宇宙学模型

IF 2.8 4区物理与天体物理

General Relativity and Gravitation Pub Date : 2023-03-27 DOI: 10.1007/s10714-023-03103-w

M. R. Ugale, S. B. Deshmukh

引用次数: 0

Finsler pp-waves and the Penrose limit 芬斯勒pp波和彭罗斯极限

IF 2.8 4区物理与天体物理

General Relativity and Gravitation Pub Date : 2023-03-26 DOI: 10.1007/s10714-023-03101-y

Amir Babak Aazami, Miguel Ángel Javaloyes, Marcus C. Werner

引用次数: 2

A space-time calculus based on symmetric 2-spinors 基于对称2旋量的时空演算

IF 2.8 4区物理与天体物理

General Relativity and Gravitation Pub Date : 2023-03-17 DOI: 10.1007/s10714-023-03088-6

Steffen Aksteiner, Thomas Bäckdahl

引用次数: 1

Hidden freedom in the mode expansion on static spacetimes 静态时空上模态展开的隐自由度

IF 2.8 4区物理与天体物理

General Relativity and Gravitation Pub Date : 2023-03-15 DOI: 10.1007/s10714-023-03099-3

Lissa de Souza Campos, Claudio Dappiaggi, Luca Sinibaldi

{"title":"Hidden freedom in the mode expansion on static spacetimes","authors":"Lissa de Souza Campos, Claudio Dappiaggi, Luca Sinibaldi","doi":"10.1007/s10714-023-03099-3","DOIUrl":"10.1007/s10714-023-03099-3","url":null,"abstract":"<div><p>We review the construction of ground states focusing on a real scalar field whose dynamics is ruled by the Klein–Gordon equation on a large class of static spacetimes. As in the analysis of the classical equations of motion, when enough isometries are present, via a mode expansion the construction of two-point correlation functions boils down to solving a second order, ordinary differential equation on an interval of the real line. Using the language of Sturm–Liouville theory, most compelling is the scenario when one endpoint of such interval is classified as a limit circle, as it often happens when one is working on globally hyperbolic spacetimes with a timelike boundary. In this case, beyond initial data, one needs to specify a boundary condition both to have a well-defined classical dynamics and to select a corresponding ground state. Here, we take into account boundary conditions of Robin type by using well-known results from Sturm–Liouville theory, but we go beyond the existing literature by exploring an unnoticed freedom that emerges from the intrinsic arbitrariness of secondary solutions at a limit circle endpoint. Accordingly, we show that infinitely many one-parameter families of sensible dynamics are admissible. In other words, we emphasize that physical constraints guaranteeing the construction of ground states do not, in general, fix one such state unambiguously. In addition, we provide, in full detail, an example on <span>((1 + 1))</span>-half Minkowski spacetime to spell out the rationale in a specific scenario where analytic formulae can be obtained.</p></div>","PeriodicalId":578,"journal":{"name":"General Relativity and Gravitation","volume":"55 3","pages":""},"PeriodicalIF":2.8,"publicationDate":"2023-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s10714-023-03099-3.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4621921","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 1

Late-time constraints on modified Gauss-Bonnet cosmology 修正高斯-邦纳宇宙论的后期约束

IF 2.8 4区物理与天体物理

General Relativity and Gravitation Pub Date : 2023-03-14 DOI: 10.1007/s10714-023-03092-w

Francesco Bajardi, Rocco D’Agostino

{"title":"Late-time constraints on modified Gauss-Bonnet cosmology","authors":"Francesco Bajardi, Rocco D’Agostino","doi":"10.1007/s10714-023-03092-w","DOIUrl":"10.1007/s10714-023-03092-w","url":null,"abstract":"<div><p>In this paper, we consider a gravitational action containing a combination of the Ricci scalar, <i>R</i>, and the topological Gauss-Bonnet term, <i>G</i>. Specifically, we study the cosmological features of a particular class of modified gravity theories selected by symmetry considerations, namely the <span>(f(R,G)= R^n G^{1-n})</span> model. In the context of a spatially flat, homogeneous and isotropic background, we show that the currently observed acceleration of the Universe can be addressed through geometry, hence avoiding <i>de facto</i> the shortcomings of the cosmological constant. We thus present a strategy to numerically solve the Friedmann equations in presence of pressureless matter and obtain the redshift behavior of the Hubble expansion rate. Then, to check the viability of the model, we place constraints on the free parameters of the theory by means of a Bayesian Monte Carlo method applied to late-time cosmic observations. Our results show that the <i>f</i>(<i>R</i>, <i>G</i>) model is capable of mimicking the low-redshift behavior of the standard <span>(Lambda )</span>CDM model. Finally, we investigate the energy conditions and show that, under suitable choices for the values of the cosmographic parameters, they are all violated when considering the mean value of <i>n</i> obtained from our analysis, as occurs in the case of a dark fluid.\u0000</p></div>","PeriodicalId":578,"journal":{"name":"General Relativity and Gravitation","volume":"55 3","pages":""},"PeriodicalIF":2.8,"publicationDate":"2023-03-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4875956","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: 9

The Big Bang nucleosynthesis abundances of the light elements using improved thermonuclear reaction rates 利用改进的热核反应速率的大爆炸核合成轻元素的丰度

IF 2.8 4区物理与天体物理

General Relativity and Gravitation Pub Date : 2023-03-13 DOI: 10.1007/s10714-023-03096-6

Chen Wu

引用次数: 0

Past-directed scalar field gradients and scalar-tensor thermodynamics 过去方向标量场梯度和标量张量热力学

IF 2.8 4区物理与天体物理

General Relativity and Gravitation Pub Date : 2023-03-09 DOI: 10.1007/s10714-023-03095-7

Andrea Giusti, Serena Giardino, Valerio Faraoni

引用次数: 5

New agegraphic dark energy in Brans–Dicke theory with sign changeable interaction for flat universe 平坦宇宙变符号相互作用下Brans-Dicke理论中的新年龄暗能量

IF 2.8 4区物理与天体物理

General Relativity and Gravitation Pub Date : 2023-03-08 DOI: 10.1007/s10714-023-03097-5

Pinki, Pankaj Kumar

{"title":"New agegraphic dark energy in Brans–Dicke theory with sign changeable interaction for flat universe","authors":"Pinki, Pankaj Kumar","doi":"10.1007/s10714-023-03097-5","DOIUrl":"10.1007/s10714-023-03097-5","url":null,"abstract":"<div><p>In the present study, we discuss a cosmological model considering interaction between new agegraphic dark energy and dark matter with sign changeable interaction term within the framework of Brans–Dicke theory of gravity for a flat universe. We assume the well motivated logarithmic form of Brans–Dicke scalar field in terms of the scale factor to find the cosmological parameters such as equation of state parameter, deceleration parameter and plot graphs to discuss their evolution against redshift parameter <i>z</i>. It is shown that the equation of state parameter may behave like cosmological constant for suitable values of parameters but it shows quintessence like behavior for different values of model parameters in future. The deceleration parameter shows observationally verified recent phase transition and accelerated expansion of the universe in future. The physical significance of well-known cosmological planes i.e. <span>(w-w^{prime })</span> and statefinder diagnostic is also explored for our model. The statefinder diagnostic shows that new agegraphic dark energy behaves like chaplygin gas in early time and behaves like quintessence in future. Moreover, for suitable values of parameters it behaves like cosmological constant at present. The analysis of <span>(w-w^{prime })</span> plane shows that our model shows freezing region and reaches in the vicinity of <span>(Lambda )</span>CDM model in future. Further, we apply thermodynamic analysis and found that the generalized second law of thermodynamics is satisfied with in the model.\u0000</p></div>","PeriodicalId":578,"journal":{"name":"General Relativity and Gravitation","volume":"55 3","pages":""},"PeriodicalIF":2.8,"publicationDate":"2023-03-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s10714-023-03097-5.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4346794","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Wormhole solution in modified teleparallel-Rastall gravity and energy conditions 修正遥平行时空重力和能量条件下的虫洞解

IF 2.8 4区物理与天体物理

General Relativity and Gravitation Pub Date : 2023-02-27 DOI: 10.1007/s10714-023-03093-9

N. Nazavari, K. Saaidi, A. Mohammadi

引用次数: 2

Wormhole Time Machines and Multiple Histories 虫洞时间机器和多重历史

IF 2.8 4区物理与天体物理

General Relativity and Gravitation Pub Date : 2023-02-24 DOI: 10.1007/s10714-023-03094-8

Barak Shoshany, Jared Wogan

{"title":"Wormhole Time Machines and Multiple Histories","authors":"Barak Shoshany, Jared Wogan","doi":"10.1007/s10714-023-03094-8","DOIUrl":"10.1007/s10714-023-03094-8","url":null,"abstract":"<div><p>In a previous paper, we showed that a class of time travel paradoxes which cannot be resolved using Novikov’s self-consistency conjecture can be resolved by assuming the existence of multiple histories or parallel timelines. However, our proof was obtained using a simplistic toy model, which was formulated using contrived laws of physics. In the present paper we define and analyze a new model of time travel paradoxes, which is more compatible with known physics. This model consists of a traversable Morris-Thorne wormhole time machine in 3+1 spacetime dimensions. We define the spacetime topology and geometry of the model, calculate the geodesics of objects passing through the time machine, and prove that this model inevitably leads to paradoxes which cannot be resolved using Novikov’s conjecture, but can be resolved using multiple histories. An open-source simulation of our new model using Mathematica is available for download on GitHub. We also provide additional arguments against the Novikov self-consistency conjecture by considering two new paradoxes, the switch paradox and the password paradox, for which assuming self-consistency inevitably leads to counter-intuitive consequences. Our new results provide more substantial support to our claim that if time travel is possible, then multiple histories or parallel timelines must also be possible.</p></div>","PeriodicalId":578,"journal":{"name":"General Relativity and Gravitation","volume":"55 2","pages":""},"PeriodicalIF":2.8,"publicationDate":"2023-02-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s10714-023-03094-8.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4925668","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 2