{"title":"Covariant single-field formulation of effective cosmological bounces","authors":"Marcello Miranda","doi":"10.1007/s10714-025-03357-6","DOIUrl":"10.1007/s10714-025-03357-6","url":null,"abstract":"<div><p>This study explores the feasibility of an effective Friedmann equation in removing the classical Big Bang initial singularity and replacing it with a non-singular bounce occurring at a critical energy density value. In a spatially flat, homogeneous, and isotropic universe, the effective theory is obtained by introducing a function parametrically dependent on the critical energy density. This function measures the deviation from the benchmark theory, which is recovered as the critical energy density approaches infinity. Focusing on the covariant single-field formulation in viable Horndeski gravity, our analysis shows that both the effective and the benchmark theories belong to the same scalar–tensor theory, without any additional propagating degrees of freedom: the cuscuton and extended cuscuton models.\u0000</p></div>","PeriodicalId":578,"journal":{"name":"General Relativity and Gravitation","volume":"57 1","pages":""},"PeriodicalIF":2.1,"publicationDate":"2025-01-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s10714-025-03357-6.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142991937","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}
Pravin K. Dahal, Swayamsiddha Maharana, Fil Simovic, Daniel R. Terno
{"title":"Horizon-bound objects: Kerr–Vaidya solutions","authors":"Pravin K. Dahal, Swayamsiddha Maharana, Fil Simovic, Daniel R. Terno","doi":"10.1007/s10714-024-03345-2","DOIUrl":"10.1007/s10714-024-03345-2","url":null,"abstract":"<div><p>Kerr–Vaidya metrics are the simplest dynamical axially-symmetric solutions, all of which violate the null energy condition and thus are consistent with the formation of a trapped region in finite time according to distant observers. We examine different classes of Kerr–Vaidya metrics, and find two which possess spherically-symmetric counterparts that are compatible with the finite formation time of a trapped region. These solutions describe evaporating black holes and expanding white holes. We demonstrate a consistent description of accreting black holes based on the ingoing Kerr–Vaidya metric with increasing mass, and show that the model can be extended to cases where the angular momentum to mass ratio varies. For such metrics we describe conditions on their dynamical evolution required to maintain asymptotic flatness.Pathologies are also identified in the evaporating white hole geometry in the form of an intermediate singularity accessible by timelike observers. We also describe a generalization of the equivalence between Rindler and Schwarzschild horizons to Kerr–Vaidya black holes, and describe the relevant geometric constructions.</p></div>","PeriodicalId":578,"journal":{"name":"General Relativity and Gravitation","volume":"57 1","pages":""},"PeriodicalIF":2.1,"publicationDate":"2025-01-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s10714-024-03345-2.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142991936","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}
Maria Andrade, Benedito Leandro, Thamara Policarpo
{"title":"Mass and topology of hypersurfaces in static perfect fluid spaces","authors":"Maria Andrade, Benedito Leandro, Thamara Policarpo","doi":"10.1007/s10714-025-03362-9","DOIUrl":"10.1007/s10714-025-03362-9","url":null,"abstract":"<div><p>We investigate the topological implications of stable minimal surfaces existing in a static perfect fluid space while ensuring that the fluid satisfies certain energy conditions. Based on the main findings, the topology of the level set <span>({f=c})</span> (the boundary of a stellar model) is studied, where <i>c</i> is a positive constant and <i>f</i> is the static potential of a static perfect fluid space. Bounds for the Hawking mass for the level set <span>({f=c})</span> of a static perfect fluid space are derived. Consequently, we prove an inequality that resembles the Penrose inequality for compact and non-compact static perfect fluid spaces, guaranteeing that the Hawking mass is positive for a class of surfaces in a static perfect fluid space. We will present a section dedicated to examples of static stellar models, one of them inspired by Witten’s black hole (or Hamilton’s cigar).\u0000\u0000</p></div>","PeriodicalId":578,"journal":{"name":"General Relativity and Gravitation","volume":"57 1","pages":""},"PeriodicalIF":2.1,"publicationDate":"2025-01-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142989917","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":"On the origin and fate of our universe","authors":"Cumrun Vafa","doi":"10.1007/s10714-025-03353-w","DOIUrl":"10.1007/s10714-025-03353-w","url":null,"abstract":"<div><p>This brief review, intended for high energy and astrophysics researchers, explores the implications of recent theoretical advances in string theory and the Swampland program for understanding bounds on the structure of positive potentials allowed in quantum gravity. This has a bearing on both inflationary models for the early universe as well as the fate of our universe. The paper includes a review of the dS conjecture as well as the TransPlanckian Censorship Conjecture and its relation to the species scale. We provide evidence for these principles as well as what they may lead to in terms of phenomenological predictions.</p></div>","PeriodicalId":578,"journal":{"name":"General Relativity and Gravitation","volume":"57 1","pages":""},"PeriodicalIF":2.1,"publicationDate":"2025-01-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142991273","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":"A Background Independent Algebra in Quantum Gravity","authors":"Edward Witten","doi":"10.1007/s10714-025-03360-x","DOIUrl":"10.1007/s10714-025-03360-x","url":null,"abstract":"<div><p>I consider the algebra of operators along the world line of an observer as a background independent algebra in quantum gravity.</p></div>","PeriodicalId":578,"journal":{"name":"General Relativity and Gravitation","volume":"57 1","pages":""},"PeriodicalIF":2.1,"publicationDate":"2025-01-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142989290","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":"Differential curvature invariants and event horizon detection for accelerating Kerr–Newman black holes in (anti-)de Sitter spacetime","authors":"G. V. Kraniotis","doi":"10.1007/s10714-024-03348-z","DOIUrl":"10.1007/s10714-024-03348-z","url":null,"abstract":"<div><p>We compute analytically differential curvature invariants for accelerating, rotating and charged black holes with a cosmological constant <span>(varLambda )</span>. Specifically, we compute novel closed-form expressions for the Karlhede and the Abdelqader-Lake invariants, for accelerating Kerr–Newman black holes in (anti-)de Sitter spacetime or subsets thereof with the aim of detecting physically relevant surfaces, like horizons and ergospheres. We explicitly show that some of the computed invariants of the particular class of spacetimes are vanishing at the event, Cauchy and acceleration horizons or ergosurface. Using the Bianchi identities we calculate in the Newman-Penrose tetrad formalism in closed-form the Page-Shoom curvature invariant for the general class of accelerating, rotating and charged Plebański-Demiański black holes with <span>(varLambda not =0)</span> and we prove that is zero at the relevant surfaces. For the invariants that vanish at horizon radii we show that are non-zero everywhere else, or in the case there are additional roots such roots do not affect their capability to detect the physically relevant surfaces. Such curvature invariants are locally measurable quantities and thus could allow the local experimental detection of the event and acceleration horizons or outer ergosurface. The differential invariants which are norms associated with the gradients of the first two Weyl invariants, are explored in detail. Although both locally single out the horizons, their global behaviour is also intriguing. Both reflect the background angular momentum and electric charge as the volume of space allowing a timelike gradient decreases with increasing spin and charge.</p></div>","PeriodicalId":578,"journal":{"name":"General Relativity and Gravitation","volume":"57 1","pages":""},"PeriodicalIF":2.1,"publicationDate":"2025-01-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142987811","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":"Kaluza–Klein bubble with massive scalar field","authors":"Darrell Jackson","doi":"10.1007/s10714-025-03350-z","DOIUrl":"10.1007/s10714-025-03350-z","url":null,"abstract":"<div><p>A well-known soliton (bubble) solution of five-dimensional Kaluza–Klein General Relativity is modified by imposing mass on the scalar field. By forcing the scalar field to be short-range, the failure of the original bubble solution to satisfy the equivalence principle is remedied, and the bubble acquires gravitational mass. Most importantly, the mass is quantized, even in this classical setting, and has a value <span>(m_P / (4 sqrt{alpha }))</span>, where <span>(m_P)</span> is the Planck mass, and <span>(alpha )</span> is the fine-structure constant. This result applies for any choice of scalar-field mass, as it is an attractor for the field equations.</p></div>","PeriodicalId":578,"journal":{"name":"General Relativity and Gravitation","volume":"57 1","pages":""},"PeriodicalIF":2.1,"publicationDate":"2025-01-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s10714-025-03350-z.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142981539","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}
{"title":"Cosmic evolution of Bianchi III model within Born-Infeld f(R) gravity theory","authors":"Debika Kangsha Banik, Sebika Kangsha Banik, Kalyan Bhuyan","doi":"10.1007/s10714-024-03346-1","DOIUrl":"10.1007/s10714-024-03346-1","url":null,"abstract":"<div><p>In this paper, we have put forwarded a detailed investigation on the cosmic evolution of Bianchi type III model within the realm of Born-Infeld <i>f</i>(<i>R</i>) gravity executing the Palatini approach. Using a very eminent tool known as Dynamical System Approach (DSA), we have curtailed the complexity of the non linear field equations and study the dynamics for the form <span>(f(R) =R-beta / R^n)</span>. The main focus of our work is to retrieve the sequence of cosmic evolution and to study the evolution of shear as well as spatial curvature.</p></div>","PeriodicalId":578,"journal":{"name":"General Relativity and Gravitation","volume":"57 1","pages":""},"PeriodicalIF":2.1,"publicationDate":"2025-01-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142974838","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":"Same as ever: looking for (in)variants in the black holes landscape","authors":"Carlos A. R. Herdeiro","doi":"10.1007/s10714-025-03351-y","DOIUrl":"10.1007/s10714-025-03351-y","url":null,"abstract":"<p><i>\"Is it a goose, a duck or a swan?\"</i>—asked the alien. <i>\"I do not know; and to</i> <i><u>know</u></i> <i>we have to look</i> <i><u>closer</u></i>.\"—said the earthling. <i>\"But even from here we can see it has webbed feet... so it is not a chicken.\" </i></p>","PeriodicalId":578,"journal":{"name":"General Relativity and Gravitation","volume":"57 1","pages":""},"PeriodicalIF":2.1,"publicationDate":"2025-01-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s10714-025-03351-y.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142974538","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}
{"title":"Black holes beyond General Relativity","authors":"Enrico Barausse, Jutta Kunz","doi":"10.1007/s10714-024-03333-6","DOIUrl":"10.1007/s10714-024-03333-6","url":null,"abstract":"<div><p>Here, we will discuss some ideas for possible classical/semi-classical modifications of the black hole solutions in General Relativity (GR). These modifications/extensions include black holes in higher dimensions; black holes with additional gravitational fields, or fields beyond the Standard Model of Particle Physics; black holes in alternative classical theories of gravity and in semiclassical gravity; phenomenological models that extend the GR black hole solutions.</p></div>","PeriodicalId":578,"journal":{"name":"General Relativity and Gravitation","volume":"57 1","pages":""},"PeriodicalIF":2.1,"publicationDate":"2025-01-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s10714-024-03333-6.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142968158","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}