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}
Pub Date : 2025-11-28DOI: 10.1088/1361-6382/ae1e53
Hideki Maeda
We present exact solutions describing a fake Schwarzschild black hole that cannot be distinguished from the Schwarzschild black hole by observations. They are constructed by attaching a spherically symmetric dynamical interior solution with a matter field to the Schwarzschild exterior solution at the event horizon without a lightlike thin shell. The dynamical region inside a Killing horizon of a static spherically symmetric perfect-fluid solution obeying an equation of state for can be the interior of a fake Schwarzschild black hole. The matter field inside such a black hole is an anisotropic fluid that violates at least the weak energy condition and can be interpreted as a spacelike (tachyonic) perfect fluid. While the author constructed the first model of fake Schwarzschild black holes using Semiz’s solution for , we present another one using Whittaker’s solution for in this paper. We also present a model of fake Kerr black holes whose interior is filled with a different matter field violating only the dominant energy condition. Because it contradicts the conservation theorem, this configuration of black holes is, in fact, precluded by the dominant energy condition.
{"title":"Fake Schwarzschild and Kerr black holes","authors":"Hideki Maeda","doi":"10.1088/1361-6382/ae1e53","DOIUrl":"https://doi.org/10.1088/1361-6382/ae1e53","url":null,"abstract":"We present exact solutions describing a fake Schwarzschild black hole that cannot be distinguished from the Schwarzschild black hole by observations. They are constructed by attaching a spherically symmetric dynamical interior solution with a matter field to the Schwarzschild exterior solution at the event horizon without a lightlike thin shell. The dynamical region inside a Killing horizon of a static spherically symmetric perfect-fluid solution obeying an equation of state for can be the interior of a fake Schwarzschild black hole. The matter field inside such a black hole is an anisotropic fluid that violates at least the weak energy condition and can be interpreted as a spacelike (tachyonic) perfect fluid. While the author constructed the first model of fake Schwarzschild black holes using Semiz’s solution for , we present another one using Whittaker’s solution for in this paper. We also present a model of fake Kerr black holes whose interior is filled with a different matter field violating only the dominant energy condition. Because it contradicts the conservation theorem, this configuration of black holes is, in fact, precluded by the dominant energy condition.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"14 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2025-11-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145610869","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 : 2025-11-27DOI: 10.1088/1361-6382/ae1c16
Shanshan Yin, Nils Andersson and Fabian Gittins
Next-generation gravitational-wave detectors are expected to constrain the properties of extreme density matter via observations of static and dynamical tides in binary neutron star inspirals. The required modelling is straightforward in Newtonian gravity—where the tide can be represented in terms of a sum involving the star’s oscillation modes—but not yet fully developed in general relativity—where the mode-sum approach is problematic. As a step towards more realistic models, we are motivated to explore the post-Newtonian (pN) approach to the problem (noting that the modes should still provide an adequate basis for a tidal expansion up to 2 pN order). Specifically, in this paper we develop the pN framework for neutron star oscillations and explore to what extent the results remain robust for stars in the strong-field regime. Our numerical results show that the model is accurate for low-mass stars ( ), but becomes problematic for more massive stars. However, we demonstrate that the main issues can be resolved (at the cost of abandoning the consistency of the pN expansion) allowing us to extend the calculation into the neutron star regime. For canonical neutron stars ( ) our adjusted formulation provides the fundamental mode of the star with an accuracy comparable to that of the relativistic Cowling approximation. For lower mass stars our approach performs is significantly more accurate, suggesting that a pN formulation of the tidal problem is, indeed, warranted.
{"title":"A post-Newtonian approach to neutron star oscillations","authors":"Shanshan Yin, Nils Andersson and Fabian Gittins","doi":"10.1088/1361-6382/ae1c16","DOIUrl":"https://doi.org/10.1088/1361-6382/ae1c16","url":null,"abstract":"Next-generation gravitational-wave detectors are expected to constrain the properties of extreme density matter via observations of static and dynamical tides in binary neutron star inspirals. The required modelling is straightforward in Newtonian gravity—where the tide can be represented in terms of a sum involving the star’s oscillation modes—but not yet fully developed in general relativity—where the mode-sum approach is problematic. As a step towards more realistic models, we are motivated to explore the post-Newtonian (pN) approach to the problem (noting that the modes should still provide an adequate basis for a tidal expansion up to 2 pN order). Specifically, in this paper we develop the pN framework for neutron star oscillations and explore to what extent the results remain robust for stars in the strong-field regime. Our numerical results show that the model is accurate for low-mass stars ( ), but becomes problematic for more massive stars. However, we demonstrate that the main issues can be resolved (at the cost of abandoning the consistency of the pN expansion) allowing us to extend the calculation into the neutron star regime. For canonical neutron stars ( ) our adjusted formulation provides the fundamental mode of the star with an accuracy comparable to that of the relativistic Cowling approximation. For lower mass stars our approach performs is significantly more accurate, suggesting that a pN formulation of the tidal problem is, indeed, warranted.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"21 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2025-11-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145609858","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 : 2025-11-27DOI: 10.1088/1361-6382/ae1b60
Xiaoyi Liu, Harvey S Reall, Jorge E Santos and Toby Wiseman
We consider Lorentzian general relativity in a cavity with a timelike boundary, with conformal boundary conditions and also a generalization of these boundary conditions. We focus on the linearized gravitational dynamics about the static empty cavity whose boundary has spherical spatial geometry. It has been recently shown that there exist dynamical instabilities, whose angular dependence is given in terms of spherical harmonics , and whose coefficient of exponential growth in time goes as . We use these modes to construct a sequence of solutions for which the initial data converge to zero as but for which the solution itself does not converge to zero. This implies a lack of continuity of solutions on initial data, which shows that the initial value problem with these boundary conditions is not well-posed. This is in tension with recent mathematical work on well-posedness for such boundary conditions.
{"title":"Ill-posedness of the Cauchy problem for linearized gravity in a cavity with conformal boundary conditions","authors":"Xiaoyi Liu, Harvey S Reall, Jorge E Santos and Toby Wiseman","doi":"10.1088/1361-6382/ae1b60","DOIUrl":"https://doi.org/10.1088/1361-6382/ae1b60","url":null,"abstract":"We consider Lorentzian general relativity in a cavity with a timelike boundary, with conformal boundary conditions and also a generalization of these boundary conditions. We focus on the linearized gravitational dynamics about the static empty cavity whose boundary has spherical spatial geometry. It has been recently shown that there exist dynamical instabilities, whose angular dependence is given in terms of spherical harmonics , and whose coefficient of exponential growth in time goes as . We use these modes to construct a sequence of solutions for which the initial data converge to zero as but for which the solution itself does not converge to zero. This implies a lack of continuity of solutions on initial data, which shows that the initial value problem with these boundary conditions is not well-posed. This is in tension with recent mathematical work on well-posedness for such boundary conditions.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"194 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2025-11-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145609857","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 : 2025-11-26DOI: 10.1088/1361-6382/ae153f
D Diksha, A Amato, V Spagnuolo, S Roorda, M Chicoine, I W Martin and J Steinlechner
Due to its low mechanical loss and high refractive index, amorphous silicon is a very promising material to realize highly-reflective coatings with low thermal-noise, such as required for gravitational-wave detection. However, the optical absorption of amorphous silicon is too high, leading to heating of cryogenically cooled mirrors. Previous work on reducing the optical absorption has indicated correlations of the absorption with deposition parameters, post-deposition treatment and possibly the SiO2-substrate type the coatings were deposited on. In this article, we present a systematic study of the optical properties of amorphous silicon, showing a correlation of the optical absorption with the band-gap energy and with Urbach tails, and disproving previously suspected correlations with the SiO2-substrate type.
{"title":"Urbach tails and optical absorption of amorphous silicon coatings","authors":"D Diksha, A Amato, V Spagnuolo, S Roorda, M Chicoine, I W Martin and J Steinlechner","doi":"10.1088/1361-6382/ae153f","DOIUrl":"https://doi.org/10.1088/1361-6382/ae153f","url":null,"abstract":"Due to its low mechanical loss and high refractive index, amorphous silicon is a very promising material to realize highly-reflective coatings with low thermal-noise, such as required for gravitational-wave detection. However, the optical absorption of amorphous silicon is too high, leading to heating of cryogenically cooled mirrors. Previous work on reducing the optical absorption has indicated correlations of the absorption with deposition parameters, post-deposition treatment and possibly the SiO2-substrate type the coatings were deposited on. In this article, we present a systematic study of the optical properties of amorphous silicon, showing a correlation of the optical absorption with the band-gap energy and with Urbach tails, and disproving previously suspected correlations with the SiO2-substrate type.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"203 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2025-11-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145599356","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 : 2025-11-26DOI: 10.1088/1361-6382/ae2059
Susobhan Mandal and S Shankaranarayanan
The accelerated expansion of the Universe poses a significant challenge to General Relativity. Non-local modifications to gravity have emerged as a compelling class of theories to address this dark energy puzzle. Building upon earlier proposals (Deser and Woodard 2007 Phys. Rev. Lett.99 111301; Deser and Woodard 2013 J. Cosmol. Astropart. Phys.11 036; Dodelson and Park 2014 Phys. Rev. D90 043535; Maggiore and Mancarella Phys. Rev. D90 023005; Capozziello and Bajardi 2022 Int. J. Mod. Phys. D31 2230009; Modesto and Tsujikawa 2013 Phys. Lett. B727 48–56; Nojiri et al 2020 Phys. Dark Univ.28 100541; Nojiri and Odintsov 2008 Phys. Lett. B659 821–826; Elizalde et al 2018 Int. J. Geom. Methods Mod. Phys.15 1850188; Jhingan et al 2008 Phys. Lett. B663 424–428), we investigate a specific non-local modified gravity action incorporating terms like , , and demonstrate that it provides a dynamical origin for a massive graviton by reducing to the standard and extended Fierz–Pauli action at the linearized level. A fixed-point analysis of the background cosmology reveals a stable de Sitter attractor, ensuring the model naturally drives accelerated expansion. Crucially, we investigate the cosmological perturbations and show that the theory’s six propagating degrees of freedom are free from ghost instabilities. We further demonstrate that all large-scale tensor modes are dynamically stable and decay on the accelerating background. This ghost-free massive gravity extension provides distinct predictions for gravitational wave polarizations and is theoretically consistent with at late times, positioning it as a unique alternative to scalar-tensor models like f(R) and Galileons. This robust stability at both the background and perturbative levels establishes our model as a consistent and compelling alternative to the standard ΛCDM paradigm.
宇宙的加速膨胀对广义相对论提出了重大挑战。引力的非局部修正已经成为解决这一暗能量之谜的一类引人注目的理论。在早期建议的基础上(Deser and Woodard 2007；Rev. letter .99 111301；Deser and Woodard 2013 J. Cosmol。Astropart。Phys.11 036;Dodelson和Park 2014物理。Rev. D90 043535；马焦雷和曼卡雷拉物理学。Rev. D90 023005；Capozziello and Bajardi 2022 Int。J.莫德：物理学。D31 2230009;Modesto and Tsujikawa 2013物理学。列托人。B727 48-56;Nojiri等2020物理学。黑暗宇宙28 100541；Nojiri和Odintsov 2008物理学。列托人。B659 821 - 826;Elizalde等2018；j .几何学。方法：物理学报15 1850188；Jhingan et al . 2008物理学。列托人。B663 424-428)，我们研究了一种特殊的非局部修正重力作用，包括，，并通过在线性化水平上简化为标准和扩展的Fierz-Pauli作用，证明了它为大质量引力子提供了一个动力学起源。背景宇宙学的定点分析揭示了一个稳定的德西特吸引子，确保模型自然地驱动加速膨胀。至关重要的是，我们研究了宇宙学扰动，并表明该理论的六个传播自由度不受幽灵不稳定性的影响。我们进一步证明了所有的大尺度张量模在加速背景下都是动态稳定和衰减的。这种无幽灵的大质量引力扩展为引力波极化提供了独特的预测，并且在理论上与后期一致，将其定位为标量张量模型（如f(R)和伽利略）的独特替代方案。这种在背景和扰动水平上的稳健稳定性使我们的模型成为标准ΛCDM范式的一致和令人信服的替代方案。
{"title":"A non-local origin for massive gravity and late-time acceleration","authors":"Susobhan Mandal and S Shankaranarayanan","doi":"10.1088/1361-6382/ae2059","DOIUrl":"https://doi.org/10.1088/1361-6382/ae2059","url":null,"abstract":"The accelerated expansion of the Universe poses a significant challenge to General Relativity. Non-local modifications to gravity have emerged as a compelling class of theories to address this dark energy puzzle. Building upon earlier proposals (Deser and Woodard 2007 Phys. Rev. Lett.99 111301; Deser and Woodard 2013 J. Cosmol. Astropart. Phys.11 036; Dodelson and Park 2014 Phys. Rev. D90 043535; Maggiore and Mancarella Phys. Rev. D90 023005; Capozziello and Bajardi 2022 Int. J. Mod. Phys. D31 2230009; Modesto and Tsujikawa 2013 Phys. Lett. B727 48–56; Nojiri et al 2020 Phys. Dark Univ.28 100541; Nojiri and Odintsov 2008 Phys. Lett. B659 821–826; Elizalde et al 2018 Int. J. Geom. Methods Mod. Phys.15 1850188; Jhingan et al 2008 Phys. Lett. B663 424–428), we investigate a specific non-local modified gravity action incorporating terms like , , and demonstrate that it provides a dynamical origin for a massive graviton by reducing to the standard and extended Fierz–Pauli action at the linearized level. A fixed-point analysis of the background cosmology reveals a stable de Sitter attractor, ensuring the model naturally drives accelerated expansion. Crucially, we investigate the cosmological perturbations and show that the theory’s six propagating degrees of freedom are free from ghost instabilities. We further demonstrate that all large-scale tensor modes are dynamically stable and decay on the accelerating background. This ghost-free massive gravity extension provides distinct predictions for gravitational wave polarizations and is theoretically consistent with at late times, positioning it as a unique alternative to scalar-tensor models like f(R) and Galileons. This robust stability at both the background and perturbative levels establishes our model as a consistent and compelling alternative to the standard ΛCDM paradigm.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"89 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2025-11-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145599357","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 : 2025-11-24DOI: 10.1088/1361-6382/ae1c8d
Gabriele Barbagallo, José Luis V Cerdeira, Carmen Gómez-Fayrén and Tomás Ortín
It has recently been shown that one can derive consistent thermodynamical expressions in the Lorentzian Taub–NUT spacetime keeping the Misner-string singularities and taking into account their contributions in the Komar integrals. We show how the same results are obtained when the Misner-string singularities are removed by using Misner’s procedure because, even though the complete spacetime has no such singularities anymore, they are unavoidable in all spacelike hypersurfaces which are used in the Komar integrals. Different choices of hypersurfaces may contain different strings and lead to different physics, though.
{"title":"A note on the calculation of the Komar integral in the Lorentzian Taub–NUT spacetime","authors":"Gabriele Barbagallo, José Luis V Cerdeira, Carmen Gómez-Fayrén and Tomás Ortín","doi":"10.1088/1361-6382/ae1c8d","DOIUrl":"https://doi.org/10.1088/1361-6382/ae1c8d","url":null,"abstract":"It has recently been shown that one can derive consistent thermodynamical expressions in the Lorentzian Taub–NUT spacetime keeping the Misner-string singularities and taking into account their contributions in the Komar integrals. We show how the same results are obtained when the Misner-string singularities are removed by using Misner’s procedure because, even though the complete spacetime has no such singularities anymore, they are unavoidable in all spacelike hypersurfaces which are used in the Komar integrals. Different choices of hypersurfaces may contain different strings and lead to different physics, though.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"10 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2025-11-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145583580","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 : 2025-11-24DOI: 10.1088/1361-6382/ae1b61
Yuta Michimura, Koji Nagano, Kentaro Komori, Kiwamu Izumi, Takahiro Ito, Satoshi Ikari, Tomotada Akutsu, Masaki Ando, Isao Kawano, Mitsuru Musha and Shuichi Sato
DECIGO (DECi-hertz Interferometer Gravitational Wave Observatory) is a space-based gravitational wave antenna concept targeting the 0.1–10 Hz band. It consists of three spacecraft arranged in an equilateral triangle with 1000 km sides, forming Fabry–Pérot cavities between them. A precursor mission, B-DECIGO, is also planned, featuring a smaller 100 km triangle. Operating these cavities requires ultra-precise formation flying, where inter-mirror distance and alignment must be precisely controlled. Achieving this necessitates a sequential improvement in precision using various sensors and actuators, from the deployment of the spacecraft to laser link acquisition and ultimately to the control of the Fabry–Pérot cavities to maintain resonance. In this paper, we derive the precision requirements at each stage and discuss the feasibility of achieving them. We show that the relative speed between cavity mirrors must be controlled at the sub-micrometer-per-second level and that relative alignment must be maintained at the sub-microradian level to obtain control signals from the Fabry–Pérot cavities of DECIGO and B-DECIGO.
{"title":"Initial acquisition requirements for optical cavities in the space gravitational wave antennae DECIGO and B-DECIGO","authors":"Yuta Michimura, Koji Nagano, Kentaro Komori, Kiwamu Izumi, Takahiro Ito, Satoshi Ikari, Tomotada Akutsu, Masaki Ando, Isao Kawano, Mitsuru Musha and Shuichi Sato","doi":"10.1088/1361-6382/ae1b61","DOIUrl":"https://doi.org/10.1088/1361-6382/ae1b61","url":null,"abstract":"DECIGO (DECi-hertz Interferometer Gravitational Wave Observatory) is a space-based gravitational wave antenna concept targeting the 0.1–10 Hz band. It consists of three spacecraft arranged in an equilateral triangle with 1000 km sides, forming Fabry–Pérot cavities between them. A precursor mission, B-DECIGO, is also planned, featuring a smaller 100 km triangle. Operating these cavities requires ultra-precise formation flying, where inter-mirror distance and alignment must be precisely controlled. Achieving this necessitates a sequential improvement in precision using various sensors and actuators, from the deployment of the spacecraft to laser link acquisition and ultimately to the control of the Fabry–Pérot cavities to maintain resonance. In this paper, we derive the precision requirements at each stage and discuss the feasibility of achieving them. We show that the relative speed between cavity mirrors must be controlled at the sub-micrometer-per-second level and that relative alignment must be maintained at the sub-microradian level to obtain control signals from the Fabry–Pérot cavities of DECIGO and B-DECIGO.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"112 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2025-11-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145583579","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 : 2025-11-24DOI: 10.1088/1361-6382/ae1d0a
Lorenzo Gavassino
Landau’s criterion for superfluidity is a special case of a broader principle: A moving fluid cannot be stopped by frictional forces if its state of motion is a local minimum of the grand potential. We employ this general thermodynamic criterion to derive a set of inequalities that any superfluid mixture (with an arbitrary number of order parameters) must satisfy for a certain state of motion to be long-lived and unimpeded by friction. These macroscopic constraints complement Landau’s original criterion, in that they hold at all temperatures, and remain valid even for gapless superfluids. They are only necessary conditions for the existence of a frictionless hydrodynamic motion, since they presuppose the validity of a fluid description, but they provide sufficient conditions for stability against stochastic hydrodynamic fluctuations. We first formulate our analysis within General Relativity (with neutron star applications in mind), and then we take the Newtonian limit.
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