General Relativity and Gravitation最新文献_第5页

Optical appearance of regularized compact objects without an exterior photon sphere 没有外部光子球的正则化致密物体的光学外观

IF 3 4区物理与天体物理

General Relativity and Gravitation Pub Date : 2026-07-26 DOI: 10.1007/s10714-026-03591-6

Ashok B. Joshi, Vishva Patel, Parth C. Varasani

{"title":"Optical appearance of regularized compact objects without an exterior photon sphere","authors":"Ashok B. Joshi, Vishva Patel, Parth C. Varasani","doi":"10.1007/s10714-026-03591-6","DOIUrl":"10.1007/s10714-026-03591-6","url":null,"abstract":"<div><p>Recent observations by the Event Horizon Telescope (EHT) indicate that the shadow of the compact object at our Galaxy’s center (Sgr A*) closely resembles that of a Schwarzschild black hole. However, identifying the presence and exact location of unstable circular null geodesics outside the compact object (hereafter referred to as an exterior exterior photon sphere) observationally remains challenging. Motivated by this, we investigate shadow formation in spacetimes that lack an exterior photon sphere by applying the Simpson–Visser (SV) regularization technique (originally designed to smooth black hole singularities) to null singularity and charged null singularity metrics. We show that the regularized null and charged null singularity spacetimes exhibit shadow-like features despite the absence of an exterior exterior photon sphere. We analyze how the SV regularization parameter influences their geometry and shadow size, and show that the regularized null and charged null singularity spacetimes can correspond either to two-way traversable wormholes or retain singularities. For the wormhole branch, the spacetime admits an unstable null orbit at the throat while remaining free of an exterior exterior photon sphere. Apart from the shadow-like dark region without an exterior photon sphere in the charged SV spacetime, our investigation shows that, for a specific range of parameters, the shadow boundary (dark region) is controlled by the regular core rather than by an exterior photon sphere. Our results reveal that shadows arising from these regularized null singularity spacetimes closely mimic those of Schwarzschild and charged black-bounce spacetimes, even though no exterior exterior photon sphere exists. We also perform a phenomenological comparison of the predicted shadow sizes with the EHT observations of Sgr A* and M87, identifying parameter ranges compatible with the observed angular diameters.</p></div>","PeriodicalId":578,"journal":{"name":"General Relativity and Gravitation","volume":"58 8","pages":""},"PeriodicalIF":3.0,"publicationDate":"2026-07-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148586772","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}

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Hilbert’s 6th problem: the relativistic version 希尔伯特的第六个问题：相对论的版本

IF 3 4区物理与天体物理

General Relativity and Gravitation Pub Date : 2026-07-26 DOI: 10.1007/s10714-026-03590-7

Michael K.-H. Kiessling

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Acoustic horizons and the Hawking effect in polariton fluids of light 光的极化流体中的声学视界和霍金效应

IF 3 4区物理与天体物理

General Relativity and Gravitation Pub Date : 2026-07-24 DOI: 10.1007/s10714-026-03586-3

Maxime J. Jacquet, Elisabeth Giacobino

{"title":"Acoustic horizons and the Hawking effect in polariton fluids of light","authors":"Maxime J. Jacquet, Elisabeth Giacobino","doi":"10.1007/s10714-026-03586-3","DOIUrl":"10.1007/s10714-026-03586-3","url":null,"abstract":"<div><p>These lecture notes develop polariton fluids of light as programmable simulators of quantum fields on tailored curved spacetimes, with emphasis on acoustic horizons and the Hawking effect. After introducing exciton-polariton physics in semiconductor microcavities, we detail the theoretical tools to study the mean field and the quantum hydrodynamics of this driven-dissipative quantum system. We derive the mapping to relativistic field theories and cast horizon physics as a pseudounitary stationary scattering problem. We present the Gaussian optics circuit that describes observables and fixes detection weights for the horizon modes in near- and far-field measurements. We provide a practical experimental toolkit (phase-imprinted flows, coherent pump-probe spectroscopy, balanced and homodyne detection) and a step-by-step workflow to extract amplification, quadrature squeezing, and entanglement among correlations. Finally, we discuss the potential of this platform to investigate open questions in quantum field theory in curved spacetime, such as near horizon effects and quasinormal modes, as well as other phenomena universal to rotating geometries, from rotational superradiance to dynamical instabilities. We further outline the interplay between rotational superradiance and the Hawking effect, proposing to spatially resolve measurements as a roadmap for ‘dumb hole spectroscopy’ and the study of entanglement dynamics in curved spacetimes.\u0000</p></div>","PeriodicalId":578,"journal":{"name":"General Relativity and Gravitation","volume":"58 8","pages":""},"PeriodicalIF":3.0,"publicationDate":"2026-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148587082","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Hierarchical formulation of the self-gravitating, n-dimensional, charged scalar field in spherical symmetry in affine null formalism 仿射零形式下球面对称自引力n维带电标量场的层次表述

IF 3 4区物理与天体物理

General Relativity and Gravitation Pub Date : 2026-07-24 DOI: 10.1007/s10714-026-03592-5

Laura Bridera, Emanuel Gallo, Thomas Mädler

引用次数: 0

Dynamics of spinning test bodies in the Schwarzschild space-time: reduction and circular orbits 史瓦西时空中自旋试验体的动力学：约简和圆轨道

IF 3 4区物理与天体物理

General Relativity and Gravitation Pub Date : 2026-07-23 DOI: 10.1007/s10714-026-03593-4

Ivan Bizyaev

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Two discs and a missing triangle: the maximally extended Kerr black hole revisited 两个圆盘和一个缺失的三角形：最大扩展的克尔黑洞重新审视

IF 3 4区物理与天体物理

General Relativity and Gravitation Pub Date : 2026-07-21 DOI: 10.1007/s10714-026-03587-2

M. A. H. MacCallum

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Intrinsic rigidity of extremal horizons and black hole uniqueness 极限视界的固有刚性和黑洞的唯一性

IF 3 4区物理与天体物理

General Relativity and Gravitation Pub Date : 2026-07-07 DOI: 10.1007/s10714-026-03584-5

James Lucietti

引用次数: 0

Tidal deformations of general-relativistic multifluid compact stars 广义相对论多流体致密恒星的潮汐变形

IF 3 4区物理与天体物理

General Relativity and Gravitation Pub Date : 2026-07-06 DOI: 10.1007/s10714-026-03582-7

Ethan Carlier, Nicolas Chamel

{"title":"Tidal deformations of general-relativistic multifluid compact stars","authors":"Ethan Carlier, Nicolas Chamel","doi":"10.1007/s10714-026-03582-7","DOIUrl":"10.1007/s10714-026-03582-7","url":null,"abstract":"<div><p>Over the past decade, gravitational-wave astronomy has opened a new window onto the extreme states of matter inside compact stars. At some point during the inspiral of a binary system, each star starts to experience adiabatic tides, characterized by tidal deformabilities. The dominant gravitoelectric quadrupolar tidal deformability, first measured with the famous GW170817 binary neutron-star merger event, has already constrained the dense-matter equation of state. With the advent of third-generation detectors, tidal deformabilities are expected to be inferred with much higher precision, potentially revealing subleading tidal contributions. This motivates the development of more accurate compact-star models that incorporate richer microphysics. With this in mind, we move beyond the commonly adopted perfect-fluid approximation and model compact stars through a multifluid framework that captures a broader set of microscopic properties. In this work, we present the fully general-relativistic description of adiabatic tidal deformations of compact stars composed of an arbitrary number of interacting fluids, using Carter’s multifluid variational formalism. A distinctive feature of this approach is the presence of nondissipative mutual entrainment between fluid species. We derive the hydrostatic equilibrium equations for multifluid configurations, along with the perturbed equations governing stationary gravitoelectric and gravitomagnetic tidal responses of arbitrary order. We then investigate how entrainment modifies the corresponding tidal deformabilities. Using an analytical representation of the multifluid equation of state, we show that entrainment leaves adiabatic tidal responses unchanged and therefore produces no measurable effect on the gravitational-wave signal emitted during the inspiral long before the excitation of internal mode resonances. We subsequently discuss two specific applications: superfluid neutron stars, and dark matter admixed compact stars.</p></div>","PeriodicalId":578,"journal":{"name":"General Relativity and Gravitation","volume":"58 7","pages":""},"PeriodicalIF":3.0,"publicationDate":"2026-07-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148409076","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Hypersurface anchored variational principle for general relativity 广义相对论的超曲面锚定变分原理

IF 3 4区物理与天体物理

General Relativity and Gravitation Pub Date : 2026-07-01 DOI: 10.1007/s10714-026-03581-8

Prasanta Sahoo

{"title":"Hypersurface anchored variational principle for general relativity","authors":"Prasanta Sahoo","doi":"10.1007/s10714-026-03581-8","DOIUrl":"10.1007/s10714-026-03581-8","url":null,"abstract":"<div><p>A hypersurface anchored variational extension of General Relativity is formulated in which the Einstein-Hilbert action is supplemented by a diffeomorphism invariant functional supported on an embedded spacelike hypersurface whose embedding is varied independently of the spacetime metric. The resulting Euler-Lagrange system consists of the Einstein equations with a localized distributional contribution together with an anchoring equation determining admissible embeddings. For the admissible class of hypersurface functionals considered here, the bulk field equations retain the standard second order principal structure away from the hypersurface and no additional propagating bulk gravitational degrees of freedom are introduced. Under ellipticity and invertibility assumptions, local persistence and linear stability of anchoring hypersurfaces follow from standard implicit function and elliptic estimates. The anchoring condition is generically inequivalent to local slicing gauge conditions and therefore defines a genuine variational restriction rather than a coordinate choice. In the canonical formulation, the momentum constraints retain their standard form, whereas the Hamiltonian constraint acquires a hypersurface supported term. The corresponding smeared generators close in the weak sense: the Dirac algebra is recovered in the bulk, with deviations confined to localized distributional surface contributions. The construction therefore defines a constrained sector of the classical solution space of General Relativity consisting of spacetimes that admit at least one embedded hypersurface satisfying the anchoring equation. In homogeneous cosmology, the localized term induces matching conditions across the anchoring surface, allowing finite transitions in the expansion rate while preserving standard evolution away from the transition hypersurface.</p></div>","PeriodicalId":578,"journal":{"name":"General Relativity and Gravitation","volume":"58 7","pages":""},"PeriodicalIF":3.0,"publicationDate":"2026-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148355672","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

The effective speed of sound in cosmological perturbation theory 宇宙微扰理论中声音的有效速度

IF 3 4区物理与天体物理

General Relativity and Gravitation Pub Date : 2026-07-01 DOI: 10.1007/s10714-026-03583-6

Sanil Unnikrishnan

{"title":"The effective speed of sound in cosmological perturbation theory","authors":"Sanil Unnikrishnan","doi":"10.1007/s10714-026-03583-6","DOIUrl":"10.1007/s10714-026-03583-6","url":null,"abstract":"<div><p>In a multi-field/fluid cosmological system consisting of minimally coupled canonical scalar fields, non-canonical scalar fields, and barotropic perfect fluids, we introduce a new definition for the effective speed of sound of the entire system to describe the evolution of cosmological perturbations. This effective speed of sound is not only gauge-invariant but also a background-dependent quantity; it can, therefore, be treated as a parameter to quantify perturbations in such multi-field/fluid systems. It is with this effective speed that the gauge-invariant Bardeen potential and the curvature perturbation propagate at scales much smaller than the sound horizon. Furthermore, the effective speed of sound defined in this paper generalizes the definition provided by Garriga and Mukhanov for a single non-canonical scalar field to a system consisting of multiple minimally coupled barotropic perfect fluids, canonical scalar fields, and non-canonical scalar fields. Moreover, as in the case of a single pure-kinetic non-canonical scalar field, this effective speed of sound for the total system turns out to be identically equal to the total adiabatic speed of sound when the dynamics of the universe are driven by multiple pure-kinetic non-canonical scalar fields. This makes such a system tantamount to a system of equivalent multi-barotropic perfect fluids. We also derive a set of equations governing the evolution of perturbations in a general multi-field/fluid universe. Using these equations, we demonstrate that in the large-scale limit (<span>(k rightarrow 0)</span>), if the perturbations are initially adiabatic, they remain so at those scales throughout the evolution of the universe, thus extending this well-known result to a general multi-field/fluid system consisting of non-canonical scalar fields. Consequently, at those scales, such a multi-field/fluid universe dynamically behaves as if it contains only a single barotropic perfect fluid.</p></div>","PeriodicalId":578,"journal":{"name":"General Relativity and Gravitation","volume":"58 7","pages":""},"PeriodicalIF":3.0,"publicationDate":"2026-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148380596","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0