Pub Date : 2025-12-05DOI: 10.1088/1361-6382/ae22b6
Brien C Nolan
Yes and maybe. In contrast to the fluid particles of this perfect fluid spacetime which follow non-geodesic world-lines and escape to infinity, we prove that freely-falling test particles of McVittie spacetime can reach the black hole horizon in finite proper time. We review the relevant evidence and argue that the fate of an extended test body is less clear. More precisely: we consider expanding McVittie spacetimes with a non-negative cosmological constant. In each member of this class, we identify a region of the spacetime such that an observer following an initially-ingoing timelike geodesic crosses the black hole horizon of the spacetime in a finite amount of proper time. The curvature behaves in interesting ways along these geodesics. In the case of a positive cosmological constant, curvature scalars (of zero, first and second order in derivatives), Jacobi fields and parallel propagated (p.p.) frame components of the curvature remain finite along timelike geodesics running into the black hole horizon. For a vanishing cosmological constant, scalar curvature terms of zero and first order as well as Jacobi fields remain finite in this limit. However, scalar curvature terms of second order diverge, and we show that there are p.p. frame components of the curvature tensor that also diverge in this limit. We argue that this casts a doubt as to whether or not an extended test body can survive crossing the black hole horizon in this case.
{"title":"Can you fall into a McVittie black hole? Will you survive?","authors":"Brien C Nolan","doi":"10.1088/1361-6382/ae22b6","DOIUrl":"https://doi.org/10.1088/1361-6382/ae22b6","url":null,"abstract":"Yes and maybe. In contrast to the fluid particles of this perfect fluid spacetime which follow non-geodesic world-lines and escape to infinity, we prove that freely-falling test particles of McVittie spacetime can reach the black hole horizon in finite proper time. We review the relevant evidence and argue that the fate of an extended test body is less clear. More precisely: we consider expanding McVittie spacetimes with a non-negative cosmological constant. In each member of this class, we identify a region of the spacetime such that an observer following an initially-ingoing timelike geodesic crosses the black hole horizon of the spacetime in a finite amount of proper time. The curvature behaves in interesting ways along these geodesics. In the case of a positive cosmological constant, curvature scalars (of zero, first and second order in derivatives), Jacobi fields and parallel propagated (p.p.) frame components of the curvature remain finite along timelike geodesics running into the black hole horizon. For a vanishing cosmological constant, scalar curvature terms of zero and first order as well as Jacobi fields remain finite in this limit. However, scalar curvature terms of second order diverge, and we show that there are p.p. frame components of the curvature tensor that also diverge in this limit. We argue that this casts a doubt as to whether or not an extended test body can survive crossing the black hole horizon in this case.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"4 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2025-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145673598","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2025-12-05DOI: 10.1088/1361-6382/ae22b4
Neven Bilić, Dragoljub D Dimitrijević, Goran S Djordjević, Milan Milošević and Marko Stojanović
The local primordial density fluctuations caused by quantum vacuum fluctuations during inflation grow into stars and galaxies in the late Universe and, if they are large enough, also produce primordial black holes (BHs). We study the formation of the primordial BHs in k-essence inflation models with a potential characterized by an inflection point. The background and perturbation equations are integrated numerically for two specific models. Using the critical collapse and peaks formalism, we calculate the abundance of primordial BHs today.
{"title":"Primordial black hole formation in k-inflation models","authors":"Neven Bilić, Dragoljub D Dimitrijević, Goran S Djordjević, Milan Milošević and Marko Stojanović","doi":"10.1088/1361-6382/ae22b4","DOIUrl":"https://doi.org/10.1088/1361-6382/ae22b4","url":null,"abstract":"The local primordial density fluctuations caused by quantum vacuum fluctuations during inflation grow into stars and galaxies in the late Universe and, if they are large enough, also produce primordial black holes (BHs). We study the formation of the primordial BHs in k-essence inflation models with a potential characterized by an inflection point. The background and perturbation equations are integrated numerically for two specific models. Using the critical collapse and peaks formalism, we calculate the abundance of primordial BHs today.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"71 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2025-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145673596","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2025-12-05DOI: 10.1088/1361-6382/ae2378
Jeferson de Oliveira, A B Pavan, Kai Lin and Yu-Hao Cui
In this work, some properties of spherically symmetric charged black holes in Bumblebee gravity are studied and analyzed. The evolution of massive and massless scalar fields around these black holes indicates their stability for σ > 0. We identify two distinct behaviors in the late-time decay: massive fields exhibit an oscillatory polynomial tail, while massless fields present a purely polynomial tail when . The duration of the ringdown phase increases with the Lorentz-violating parameter σ. The real part of the quasinormal modes is less sensitive to Lorentz symmetry breaking than the imaginary part. Regarding the optical appearance of the black hole, the Lorentz-violating parameter reduces its luminosity while simultaneously increasing the radial extent of the accretion disk.
{"title":"Scalar quasinormal modes, late-time tails and optical appearance of charged black holes in Bumblebee gravity","authors":"Jeferson de Oliveira, A B Pavan, Kai Lin and Yu-Hao Cui","doi":"10.1088/1361-6382/ae2378","DOIUrl":"https://doi.org/10.1088/1361-6382/ae2378","url":null,"abstract":"In this work, some properties of spherically symmetric charged black holes in Bumblebee gravity are studied and analyzed. The evolution of massive and massless scalar fields around these black holes indicates their stability for σ > 0. We identify two distinct behaviors in the late-time decay: massive fields exhibit an oscillatory polynomial tail, while massless fields present a purely polynomial tail when . The duration of the ringdown phase increases with the Lorentz-violating parameter σ. The real part of the quasinormal modes is less sensitive to Lorentz symmetry breaking than the imaginary part. Regarding the optical appearance of the black hole, the Lorentz-violating parameter reduces its luminosity while simultaneously increasing the radial extent of the accretion disk.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"29 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2025-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145673601","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2025-12-02DOI: 10.1088/1361-6382/ae217f
Zhi-Jie Lu, Teng-Yu Long, Wen-Hai Tan, Min-Na Qiao, Ming-Guang Fu, Jian-Ping Liu and Shan-Qing Yang
Torsion pendulums have vital applications in gravitational experiments. Seismic cross-coupling is one of the important noises, which can be suppressed by the eddy current damper, but this technology is still inadequate for torsion pendulums suspended by high-Q fused silica fiber. In this paper, we analyze the seismic cross-coupling for different-shaped torsion pendulums with eddy current dampers. The nonlinear coupling of the high-frequency vibration to the low-frequency twist oscillation is demonstrated. The impact of the pendulum’s asymmetry and the damping is discussed. We evaluated the seismic coupling noise on a torsion pendulum in our underground laboratory obtaining at 1 mHz for a hollow cubic test mass, and for a rectangle bar pendulum, it increases to , much larger than the thermal noise of the silica fiber. For the seismic cross-coupling noise in an asymmetrical pendulum, we propose a novel common-mode rejection method with two similar pendulums, where one is used as a reference, and the other responds to the scientific signal. For the rectangle bar pendulum, about one order of magnitude suppression can be realized, with the noise level reaching in the mHz frequency band.
{"title":"Research of the seismic coupling to the torsion pendulum and a common-mode rejection method","authors":"Zhi-Jie Lu, Teng-Yu Long, Wen-Hai Tan, Min-Na Qiao, Ming-Guang Fu, Jian-Ping Liu and Shan-Qing Yang","doi":"10.1088/1361-6382/ae217f","DOIUrl":"https://doi.org/10.1088/1361-6382/ae217f","url":null,"abstract":"Torsion pendulums have vital applications in gravitational experiments. Seismic cross-coupling is one of the important noises, which can be suppressed by the eddy current damper, but this technology is still inadequate for torsion pendulums suspended by high-Q fused silica fiber. In this paper, we analyze the seismic cross-coupling for different-shaped torsion pendulums with eddy current dampers. The nonlinear coupling of the high-frequency vibration to the low-frequency twist oscillation is demonstrated. The impact of the pendulum’s asymmetry and the damping is discussed. We evaluated the seismic coupling noise on a torsion pendulum in our underground laboratory obtaining at 1 mHz for a hollow cubic test mass, and for a rectangle bar pendulum, it increases to , much larger than the thermal noise of the silica fiber. For the seismic cross-coupling noise in an asymmetrical pendulum, we propose a novel common-mode rejection method with two similar pendulums, where one is used as a reference, and the other responds to the scientific signal. For the rectangle bar pendulum, about one order of magnitude suppression can be realized, with the noise level reaching in the mHz frequency band.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"23 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2025-12-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145651349","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2025-12-01DOI: 10.1088/1361-6382/ae1d09
Yan-Chong Liu, Qian-Ni Huang, Ming Hu, Yun Ma, Shi-Meng Yang, Zi-He Huang, Bing-Qing He and Ze-Bing Zhou
Due to the processing accuracy of the test mass (TM) in gravitational reference sensors, the electrostatic force in the non-sensitive direction of the TM will produce a cross-coupling effect in the sensitive direction. This paper quantifies the impact of TM geometric imperfections (parallelism and perpendicularity) on electrostatic cross-coupling noise. The electrostatic coupling effects are examined while the TianQin spacecraft adopts free and drag-free modes in the Z direction by examining the solar radiation pressure during the scientific operation period. In the free mode, the electrostatic force couples the low-frequency variations of solar pressure to the sensitive direction, which requires the coupling coefficient to be better than 3 × 10−6. The drag-free mode can effectively reduce the electrostatic control forces in non-sensitive directions, thereby reducing coupling effects, which the coupling coefficient requirement can be relaxed to 7.5 × 10−5. By reducing the displacement sensing noise, the requirement for coupling coefficient can be further reduced.
{"title":"Modeling and analysis of the electrostatic cross-coupling effect of the gravitational reference sensor for TianQin project","authors":"Yan-Chong Liu, Qian-Ni Huang, Ming Hu, Yun Ma, Shi-Meng Yang, Zi-He Huang, Bing-Qing He and Ze-Bing Zhou","doi":"10.1088/1361-6382/ae1d09","DOIUrl":"https://doi.org/10.1088/1361-6382/ae1d09","url":null,"abstract":"Due to the processing accuracy of the test mass (TM) in gravitational reference sensors, the electrostatic force in the non-sensitive direction of the TM will produce a cross-coupling effect in the sensitive direction. This paper quantifies the impact of TM geometric imperfections (parallelism and perpendicularity) on electrostatic cross-coupling noise. The electrostatic coupling effects are examined while the TianQin spacecraft adopts free and drag-free modes in the Z direction by examining the solar radiation pressure during the scientific operation period. In the free mode, the electrostatic force couples the low-frequency variations of solar pressure to the sensitive direction, which requires the coupling coefficient to be better than 3 × 10−6. The drag-free mode can effectively reduce the electrostatic control forces in non-sensitive directions, thereby reducing coupling effects, which the coupling coefficient requirement can be relaxed to 7.5 × 10−5. By reducing the displacement sensing noise, the requirement for coupling coefficient can be further reduced.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"22 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145645272","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2025-12-01DOI: 10.1088/1361-6382/ae1ee2
Alexandre Arbey, Etera R Livine and Clara Montagnon
In the context of the general effort to model black hole (BH) dynamics, and in particular their return-to-equilibrium through quasi-normal modes (QNMs), it is crucial to understand how much test-field perturbations deviate from physical perturbations in modified gravity scenarios. On the one hand, physical perturbations follow the modified Einstein equations of the considered extension of general relativity. The complexity of those equations can quickly escalate with extra fields and non-linear couplings. On the other hand, test-field perturbations, with negligible back-reaction on the space-time geometry, describe the propagation of both matter fields and spin s = 2 gravitational waves on the BH geometry. They are not subject to the intricacies of the modified Einstein equations, and only probe the background spacetime metric. If their physics were to not deviate significantly from physical perturbations, they would be especially useful to investigate predictions from quantum gravity scenarios which lack explicit detailed Einstein equations. Here we focus on a specific modified gravity solution—Babichev-Charmousis-Lehébel BHs in scalar–tensor theories—for which physical perturbations and related QNM frequencies have already been studied and computed numerically. We compute the test-field QNM frequencies and compare the two QNM spectra. This provides a concrete example of the significant differences arising between test-fields and physical perturbations, and flags unphysical deviations related to the test-field framework.
{"title":"Test-field vs physical quasi-normal modes in scalar–tensor theories","authors":"Alexandre Arbey, Etera R Livine and Clara Montagnon","doi":"10.1088/1361-6382/ae1ee2","DOIUrl":"https://doi.org/10.1088/1361-6382/ae1ee2","url":null,"abstract":"In the context of the general effort to model black hole (BH) dynamics, and in particular their return-to-equilibrium through quasi-normal modes (QNMs), it is crucial to understand how much test-field perturbations deviate from physical perturbations in modified gravity scenarios. On the one hand, physical perturbations follow the modified Einstein equations of the considered extension of general relativity. The complexity of those equations can quickly escalate with extra fields and non-linear couplings. On the other hand, test-field perturbations, with negligible back-reaction on the space-time geometry, describe the propagation of both matter fields and spin s = 2 gravitational waves on the BH geometry. They are not subject to the intricacies of the modified Einstein equations, and only probe the background spacetime metric. If their physics were to not deviate significantly from physical perturbations, they would be especially useful to investigate predictions from quantum gravity scenarios which lack explicit detailed Einstein equations. Here we focus on a specific modified gravity solution—Babichev-Charmousis-Lehébel BHs in scalar–tensor theories—for which physical perturbations and related QNM frequencies have already been studied and computed numerically. We compute the test-field QNM frequencies and compare the two QNM spectra. This provides a concrete example of the significant differences arising between test-fields and physical perturbations, and flags unphysical deviations related to the test-field framework.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"18 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145645306","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2025-11-28DOI: 10.1088/1361-6382/ae20eb
Hubert Bray and James Wheeler
We discuss and formalize topological means by which the initial singularity might be mollified, at the level of the spacetime manifold’s structure, in classical cosmological models of a homogeneous expanding Universe. One construction, dubbed a ‘reflective’ topological big bang, generalizes Schrödinger’s elliptic de Sitter space and is built to be compatible with the standard Friedmann–Lemaitre–Robertson–Walker picture of the large-scale Universe, only minimally modifying it via some nontrivial topology at an earliest ‘moment’ in the Universe’s history. We establish a mathematical characterization of the admissible topological structures of reflective topological big bangs, and we discuss implications for a standard concern in cosmology, the horizon problem. We present a nonreflective example that we have christened the Itty-Bitty Blender spacetime: this spacetime and its universal cover, the Eternal Trumpet spacetime, exhibit interesting potential structures of spacetimes avoiding the Hawking and Penrose singularity theorems. While these toy models provide a proof-of-concept picture, several questions remain regarding the capacity to realize these structures under physical energy conditions.
{"title":"Topological big bangs: reflection, itty-bitty blenders, and eternal trumpets","authors":"Hubert Bray and James Wheeler","doi":"10.1088/1361-6382/ae20eb","DOIUrl":"https://doi.org/10.1088/1361-6382/ae20eb","url":null,"abstract":"We discuss and formalize topological means by which the initial singularity might be mollified, at the level of the spacetime manifold’s structure, in classical cosmological models of a homogeneous expanding Universe. One construction, dubbed a ‘reflective’ topological big bang, generalizes Schrödinger’s elliptic de Sitter space and is built to be compatible with the standard Friedmann–Lemaitre–Robertson–Walker picture of the large-scale Universe, only minimally modifying it via some nontrivial topology at an earliest ‘moment’ in the Universe’s history. We establish a mathematical characterization of the admissible topological structures of reflective topological big bangs, and we discuss implications for a standard concern in cosmology, the horizon problem. We present a nonreflective example that we have christened the Itty-Bitty Blender spacetime: this spacetime and its universal cover, the Eternal Trumpet spacetime, exhibit interesting potential structures of spacetimes avoiding the Hawking and Penrose singularity theorems. While these toy models provide a proof-of-concept picture, several questions remain regarding the capacity to realize these structures under physical energy conditions.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"1 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2025-11-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145610871","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2025-11-28DOI: 10.1088/1361-6382/ae2058
Mateo Batkis, Joshua Berrier, Kevin Boyce, John Capone, Ryan Derosa, Joseph Howard, Joseph Ivanov, Craig Jones, Jason Kelly, Ritva Keski-Kuha, Joshua Lutter, Andrew Menas, Nicolas Nicolaeff, Nova Nimmo, Jonathan Papa, Shannon Sankar, Shane Wake and Andrew Weaver
The Laser Interferometer Space Antenna (LISA) will be a space-borne gravitational wave observatory that consists of three spacecraft, separated by several million kilometers, which tracks the separation between inertial test masses via laser interferometry. In this architecture strict requirements exist on the design of the orbits, the ability to accommodate laser frequency noise, the ability to provide the necessary purity of free-fall, and the quality of the optical metrology. This final item is enabled with afocal transmitting/receiving telescopes that increase the laser power transfer efficiency over the long inter-spacecraft link. These telescopes must be designed and built not to adversely affect the precision of the interferometric measurements. The function, design, and current status of LISA telescopes under development at NASA will be discussed in this article.
{"title":"Telescopes for LISA: function, current status, and path forward","authors":"Mateo Batkis, Joshua Berrier, Kevin Boyce, John Capone, Ryan Derosa, Joseph Howard, Joseph Ivanov, Craig Jones, Jason Kelly, Ritva Keski-Kuha, Joshua Lutter, Andrew Menas, Nicolas Nicolaeff, Nova Nimmo, Jonathan Papa, Shannon Sankar, Shane Wake and Andrew Weaver","doi":"10.1088/1361-6382/ae2058","DOIUrl":"https://doi.org/10.1088/1361-6382/ae2058","url":null,"abstract":"The Laser Interferometer Space Antenna (LISA) will be a space-borne gravitational wave observatory that consists of three spacecraft, separated by several million kilometers, which tracks the separation between inertial test masses via laser interferometry. In this architecture strict requirements exist on the design of the orbits, the ability to accommodate laser frequency noise, the ability to provide the necessary purity of free-fall, and the quality of the optical metrology. This final item is enabled with afocal transmitting/receiving telescopes that increase the laser power transfer efficiency over the long inter-spacecraft link. These telescopes must be designed and built not to adversely affect the precision of the interferometric measurements. The function, design, and current status of LISA telescopes under development at NASA will be discussed in this article.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"103 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2025-11-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145610872","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2025-11-28DOI: 10.1088/1361-6382/ae205a
Chiang-Mei Chen, Akihiro Ishibashi, Rituparna Mandal and Nobuyoshi Ohta
We study anisotropic Bianchi-I cosmology, incorporating quantum gravitational corrections into the Einstein equation through the scale-dependent Newton coupling and cosmological term, as determined by the flow equation of the effective action for gravity. For the classical cosmological constant Λ0 = 0, we derive the quantum mechanically corrected, or quantum-improved power-series solution for a general equation-of-state parameter w in the range in the form of expansions in both inverse cosmic time and the anisotropy parameter. We give a general criterion, valid for any Λ0, if the solution becomes isotropic in the late time, which indicates that the Universe becomes isotropic for most cases of except w = 1. By numerical analysis, we show that quantum corrections lead to earlier isotropization compared to the classical case starting from an initially highly anisotropic state. In contrast, for , we obtain the inverse power-series solution in the exponential of the cosmic time. We find that the Universe always becomes isotropic in the late time, in accordance with the cosmic no hair theorem, and the quantum corrections make the isotropization faster. We also briefly summarize the Kasner solution and its generalization with quantum corrections.
{"title":"Bianchi-I cosmology with scale dependent G and Λ in asymptotically safe gravity","authors":"Chiang-Mei Chen, Akihiro Ishibashi, Rituparna Mandal and Nobuyoshi Ohta","doi":"10.1088/1361-6382/ae205a","DOIUrl":"https://doi.org/10.1088/1361-6382/ae205a","url":null,"abstract":"We study anisotropic Bianchi-I cosmology, incorporating quantum gravitational corrections into the Einstein equation through the scale-dependent Newton coupling and cosmological term, as determined by the flow equation of the effective action for gravity. For the classical cosmological constant Λ0 = 0, we derive the quantum mechanically corrected, or quantum-improved power-series solution for a general equation-of-state parameter w in the range in the form of expansions in both inverse cosmic time and the anisotropy parameter. We give a general criterion, valid for any Λ0, if the solution becomes isotropic in the late time, which indicates that the Universe becomes isotropic for most cases of except w = 1. By numerical analysis, we show that quantum corrections lead to earlier isotropization compared to the classical case starting from an initially highly anisotropic state. In contrast, for , we obtain the inverse power-series solution in the exponential of the cosmic time. We find that the Universe always becomes isotropic in the late time, in accordance with the cosmic no hair theorem, and the quantum corrections make the isotropization faster. We also briefly summarize the Kasner solution and its generalization with quantum corrections.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"55 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2025-11-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145610873","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2025-11-28DOI: 10.1088/1361-6382/ae1e56
A Kazım Çamlıbel, M Akif Feyizoğlu and İbrahim Semiz
In this work, we revisit/reinterpret/extend the model-independent analysis method (which we now call spread—luminosity distance fitting) from our previous work. We apply it to the updated supernova type Ia catalog, Pantheon+ and recent gamma ray bursts compilations. The procedure allows us, using only Friedmann-Lemaitre-Robertson-Walker (FLRW) assumption, to construct good approximations for expansion history of the Universe, re-confirming its acceleration to be a robust feature. When we also assume general relativity (GR), we can demonstrate, without any matter/energy model in mind, the need for (possibly nonconstant) generalized dark energy (GDE). We find hints for positive pressure of GDE at z > 1 with implications on either the complexity of dark energy, or the validity of one of the cosmological principle, interpretation of SN Ia data, or GR.
{"title":"Analysis of Pantheon+ supernova data suggests evidence of sign-changing pressure of the cosmological fluid","authors":"A Kazım Çamlıbel, M Akif Feyizoğlu and İbrahim Semiz","doi":"10.1088/1361-6382/ae1e56","DOIUrl":"https://doi.org/10.1088/1361-6382/ae1e56","url":null,"abstract":"In this work, we revisit/reinterpret/extend the model-independent analysis method (which we now call spread—luminosity distance fitting) from our previous work. We apply it to the updated supernova type Ia catalog, Pantheon+ and recent gamma ray bursts compilations. The procedure allows us, using only Friedmann-Lemaitre-Robertson-Walker (FLRW) assumption, to construct good approximations for expansion history of the Universe, re-confirming its acceleration to be a robust feature. When we also assume general relativity (GR), we can demonstrate, without any matter/energy model in mind, the need for (possibly nonconstant) generalized dark energy (GDE). We find hints for positive pressure of GDE at z > 1 with implications on either the complexity of dark energy, or the validity of one of the cosmological principle, interpretation of SN Ia data, or GR.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"116 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2025-11-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145610866","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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}
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