{"title":"Black holes in the expanding Universe","authors":"Nikodem Popławski","doi":"10.1088/1361-6382/adb537","DOIUrl":"https://doi.org/10.1088/1361-6382/adb537","url":null,"abstract":"The McVittie metric does not describe a physical black hole in an expanding Universe because the curvature scalar and pressure at its event horizon are infinite. We show that extending this metric to an inhomogeneous scale factor, which depends on both the time and radial coordinate, removes those infinities by imposing at the horizon the constancy of the Hubble parameter and a particular constraint on the gradient of the scale factor. We consider a special case of this metric, and show that the Hubble parameters at the event horizons of all centrally symmetric black holes are equal to the same constant . Because of this equality and the equivalence to the Kottler metric near the horizon, black holes do not grow with the Universe expansion.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"52 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2025-03-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143546503","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}
{"title":"Gravitational radiation reaction for compact binary systems at the fourth-and-a-half post-Newtonian order","authors":"Luc Blanchet, Guillaume Faye and David Trestini","doi":"10.1088/1361-6382/adac9d","DOIUrl":"https://doi.org/10.1088/1361-6382/adac9d","url":null,"abstract":"We compute the gravitational radiation–reaction (RR) force on a compact binary source at the fourth-and-a-half post-Newtonian (4.5PN) order of general relativity, i.e. 2PN order beyond the leading 2.5PN radiation reaction. The calculation is valid for general orbits in a general frame, but in a particular coordinate system which is an extension of the Burke–Thorne coordinate system at the lowest order. With the RR acceleration, we derive (from first principles) the flux-balance laws associated with the energy, the angular and linear momenta, and the center-of-mass (CM) position, in a general frame and up to 4.5PN order. Restricting our attention to the frame of the center of mass, we point out that the equations of motion (EOM) acquire a non-local-in-time contribution at the 4.5PN order, made of the integrated flux of linear momentum (responsible for the recoil of the source) together with the instantaneous flux of CM position. The non-local contribution was overlooked in the past literature, which assumed locality of the RR force in the center of mass frame at 4.5PN order. We discuss the consequences of this non-local effect and obtain consistent non-local EOM and flux balance laws at 4.5PN order in the CM frame.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"9 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2025-03-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143538331","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}
Tong Liu, Cheng-Gang Qin, Jing-Hui Pu, Yong-Zhang Yang and Wen-Bin Wang
{"title":"Accuracy and stability study of two-way time transfer in Cis-lunar space","authors":"Tong Liu, Cheng-Gang Qin, Jing-Hui Pu, Yong-Zhang Yang and Wen-Bin Wang","doi":"10.1088/1361-6382/adb7b3","DOIUrl":"https://doi.org/10.1088/1361-6382/adb7b3","url":null,"abstract":"The realization of clock synchronization and syntonization via inter-satellite link is of vital importance for navigation, space-based Very Long Baseline Interferometry (VLBI) experiments and precision tests of fundamental physics. We study the accuracy and stability of time and frequency transfer via inter-satellite link in Cis-lunar space. A relativistic time transfer model using microwave dual one-way ranging (DOWR) is developed. Taking the distant retrograde orbit (DRO)-low Earth orbit (LEO) inter-satellite link as an instance, sub-nanoseconds level accuracy is achieved. We analyze the error in orbit determination of LEO satellite and DRO satellite. With the models of relative velocity correction, relativistic frequency shift and Shapiro delay, the stability of time transfer is studied. The result shows the DOWR microwave link would support clock synchronization with a time stability of better than 14.3 ps over 1000 s, better than 100.5 ps over one day, with the accuracy constraints on the orbit determination of the LEO satellite 10 cm and DRO satellite 50 m in position. If the longer time stability of hardware delay reaches ps level, the performance of DOWR time transfer link can be further improved to support the distribution of the time–frequency scale established by an active hydrogen maser with a frequency stability of over one day. We estimated that high-performance DRO-LEO time and frequency comparisons may support the gravitational redshift tests at a 10−6 level and the space-based VLBI experiments to improve the orbit determination of deep-space probes by one to two orders of magnitude.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"2 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2025-03-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143538459","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}
{"title":"Effect of gravitational waves on Yang-Mills condensates","authors":"Narasimha Reddy Gosala and Arundhati Dasgupta","doi":"10.1088/1361-6382/adb5ea","DOIUrl":"https://doi.org/10.1088/1361-6382/adb5ea","url":null,"abstract":"In this article, we investigate the interactions of a Yang-Mills (YM) wave fluctuation of a classical isotropic, homogeneous YM condensate, which models gluon plasma, with a gravitational wave (GW). We re-analyse the study of fluctuations of the gluon plasma using vector decomposition of the gauge field into scalar, longitudinal, and transverse modes. We find that there is an energy transfer between isotropic gluon condensate and plasmon modes, but the effect is delayed due to GW, and dependent on the initial conditions. We also study quarks in the background of YM condensate and GW. We find that the quarks break the isotropy of the condensate and the GW couples quarks of different flavours of the SU(2) group. Thus, the GW induces flavour fluctuations, which has interesting implications for experimental observations and quark-gluon plasma physics.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"5 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2025-03-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143532863","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}
Paul Stevens, Vincent Loriette, Manuel Andia, François Glotin, Angélique Lartaux-Vollard, Nicolas Leroy and Aymeric van de Walle
{"title":"Resonant behavior and stability of a linear three-mirror cavity","authors":"Paul Stevens, Vincent Loriette, Manuel Andia, François Glotin, Angélique Lartaux-Vollard, Nicolas Leroy and Aymeric van de Walle","doi":"10.1088/1361-6382/adb827","DOIUrl":"https://doi.org/10.1088/1361-6382/adb827","url":null,"abstract":"The implementation of Fabry–Perot cavities in gravitational-wave detectors has been pivotal to improving their sensitivity, allowing the observation of an increasing number of cosmological events with higher signal-to-noise ratio. Notably, Fabry–Perot cavities play a key role in the frequency-dependent squeezing technique, which provides a reduction of quantum noise over the whole observation frequency spectrum. In this paper, we first present how the adaptability of resonance properties of linear three-mirror cavities, and the real-time control we could have on it, would be interesting for frequency-dependant squeezing in future detectors, especially for Einstein Telescope project. In this view, we develop a complete model to describe the stability behavior and the properties of transmitted and reflected fields of a linear three-mirror cavity aiming to be used for design purposes. In particular, simulations are carried out to show the evolution of the characteristic double resonance peak they can show-off, which is one of the key features of this system, as a function of cavity parameters. We show that the double-peak shape is almost freely adjustable, either in terms of spacing between maxima, their relative amplitude and intrinsic width. This is made possible by changing the mirrors’ reflectivity coefficients and the sub-cavities microscopic/macroscopic lengths. However, the amount of achievable realistic configurations is limited by the stability conditions of the cavity. In particular, if the two sub-cavities do not have the same macroscopic length, it could be difficult to obtain a stable three-mirror cavity. Different geometries have been studied to obtain a stable system.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"55 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2025-03-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143532861","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}
{"title":"Kerr metric from two commuting complex structures","authors":"Kirill Krasnov and Adam Shaw","doi":"10.1088/1361-6382/adb531","DOIUrl":"https://doi.org/10.1088/1361-6382/adb531","url":null,"abstract":"The main aim of this paper is to simplify and popularise the construction from the 2013 paper by Apostolov, Calderbank and Gauduchon, which (among other things) derives the Plebański–Demiański family of solutions of GR using ideas of complex geometry. The starting point of this construction is the observation that the Euclidean versions of these metrics should have two different commuting complex structures, as well as two commuting Killing vector fields. After some linear algebra, this leads to an ansatz for the metrics, which is half-way to their complete determination. Kerr metric is a special 2-parameter subfamily in this class, which makes these considerations directly relevant to Kerr as well. This results in a derivation of the Kerr metric that is self-contained and elementary, in the sense of being mostly an exercise in linear algebra.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"211 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2025-03-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143532860","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}
{"title":"The gauge theory of Weyl group and its interpretation as Weyl quadratic gravity","authors":"Cezar Condeescu and Andrei Micu","doi":"10.1088/1361-6382/adb3e8","DOIUrl":"https://doi.org/10.1088/1361-6382/adb3e8","url":null,"abstract":"In this paper we give an extensive description of Weyl quadratic gravity as the gauge theory of the Weyl group. The previously discovered (vectorial) torsion/non-metricity equivalence is shown to be built-in as it corresponds to a redefinition of the generators of the Weyl group. We present a generalisation of the torsion/non-metricity duality which includes, aside from the vector, also a traceless 3-tensor with two antisymmetric indices and vanishing skew symmetric part. A discussion of this relation in the case of minimally coupled matter fields is given. We further point out that a Rarita–Schwinger field can couple minimally to all the components of torsion and some components of non-metricity. Alongside we present the same gauge construction for the Poincaré and conformal groups. We show that even though the Weyl group is a subgroup of the conformal group, the gauge theory of the latter is actually only a special case of Weyl quadratic gravity.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"20 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2025-02-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143518542","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}
Juan V O Pêgas, André G S Landulfo, George E A Matsas and Daniel A T Vanzella
{"title":"Globally hyperbolic evaporating black hole and the information loss issue","authors":"Juan V O Pêgas, André G S Landulfo, George E A Matsas and Daniel A T Vanzella","doi":"10.1088/1361-6382/adb534","DOIUrl":"https://doi.org/10.1088/1361-6382/adb534","url":null,"abstract":"We discuss the information loss issue for completely evaporating black holes in the context of a globally hyperbolic spacetime that maintains unchanged the entire semiclassical picture except for the ‘last evaporation breath,’ which pertains to full quantum gravity. Even though observers outside the black hole cannot access information that enters the horizon, there is no actual loss of information imposed by the spacetime causal structure since it is carried over from one Cauchy surface to the next (provided the local evolution is unitary).","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"16 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2025-02-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143506811","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}
{"title":"Geometry of Carrollian stretched horizons","authors":"Laurent Freidel and Puttarak Jai-akson","doi":"10.1088/1361-6382/adaf6e","DOIUrl":"https://doi.org/10.1088/1361-6382/adaf6e","url":null,"abstract":"In this paper, we present a comprehensive toolbox for studying Carrollian stretched horizons, encompassing their geometry, dynamics, symplectic geometry, symmetries, and corresponding Noether charges. We introduce a precise definition of ruled stretched Carrollian structures (sCarrollian structures) on any surface, generalizing the conventional Carrollian structures of null surfaces, along with the notions of sCarrollian connection and sCarrollian stress tensor. Our approach unifies the sCarrollian (intrinsic) and stretched horizon (embedding) perspectives, providing a universal framework for any causal surface, whether timelike or null. We express the Einstein equations in sCarrollian variables and discuss the phase space symplectic structure of the sCarrollian geometry. Through Noether’s theorem, we derive the Einstein equation and canonical charge and compute the evolution of the canonical charge along the transverse (radial) direction. The latter can be interpreted as a spin-2 symmetry charge. Our framework establishes a novel link between gravity on stretched horizons and Carrollian fluid dynamics and unifies various causal surfaces studied in the literature, including non-expanding and isolated horizons. We expect this work to provide insights into the hydrodynamical description of black holes and the quantization of null surfaces.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"15 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2025-02-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143506787","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}
José M Isidro, Claudio F Paganini and Alessandro Pesci
{"title":"Gravitation as a statistical theory on the light cone","authors":"José M Isidro, Claudio F Paganini and Alessandro Pesci","doi":"10.1088/1361-6382/ada967","DOIUrl":"https://doi.org/10.1088/1361-6382/ada967","url":null,"abstract":"In this paper, we will explore Padmanabhan’s mesoscopic, statistical approach to gravity (Padmanathan 2017 J. Phys.: Conf. Ser.880 012008) with a twist. The general picture of his approach is that spacetime is made of large numbers of localized quantum degrees of freedom. Padmanabhan assumed that the degrees of freedom of a given quantum state of geometry contribute, after averaging over fluctuations, a vector degree of freedom for spacetime at a point. For null vectors, this can be regarded as corresponding to one single vector, i.e. a pure state, for the statistical ensemble on the light cone at every point. In the present paper, we consider instead the case where the states of the gravitational degrees of freedom are spread out and overlap, with only probabilistic information on which of them determines the actual spacetime at a point. In the continuum limit, this corresponds to a mixed state for the statistical ensemble on the light cone at every point. This change in assumptions leads to some interesting observations. When we define a statistical ensemble on the light cone, its variance ‘knows’ about the interior of the light cone. As an intriguing consequence, we find that the cosmological constant can be related to the variance over the light cone. With a mixed state, we can no longer derive the gravitational field equations from an entropy functional. Here, instead, we show that a naive implementation of the measure of a mixed state on the light cone in the variation principle leads to modified measure theories as the grand canonical ensemble and allows one to reframe unimodular gravity as the canonical ensemble of a statistical theory on the light cone.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"14 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2025-02-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143495384","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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