Classical and Quantum Gravity最新文献

{"title":"Dynamical systems analysis of a cosmological model with interacting Umami Chaplygin fluid in adiabatic particle creation mechanism: some bouncing features","authors":"Goutam Mandal and Sujay Kr Biswas","doi":"10.1088/1361-6382/ad9f17","DOIUrl":"https://doi.org/10.1088/1361-6382/ad9f17","url":null,"abstract":"The present work aims to investigate an interacting Umami Chaplygin gas (UCG) in the background dynamics of a spatially flat Friedmann–Lemaitre–Robertson–Walker Universe when adiabatic particle creation is allowed. Here, the Universe is taken to be an open thermodynamical model where the particle is created irreversibly and consequently, the creation pressure comes into the energy-momentum tensor of the material content. The particle creation rate is assumed to have a linear relationship with the Hubble parameter ( ) and the created particle is dark matter (pressureless). With this creation rate a single fluid model studied and found no phase transition. Then, we studied an interacting two-fluid model where second fluid is taken as perfect fluid equation of state (EOS) and late-time acceleration is obtained. Next, interacting UCG is studied in context of particle creation. Dynamical stability of the model is performed by perturbing the autonomous system around critical points upto first order. Classical stability of the model is also studied at each critical point. This study explores some cosmologically viable scenarios when we constrain the model parameters. Some critical points exhibit the accelerated de Sitter expansion of the Universe at both the early phase as well as the late phase of evolution which is characterized by completely Umami Chaplygin fluid EOS. Scaling solutions are also described by some other critical points showing late-time accelerated attractors in phase space satisfying present observational data, and solving the coincidence problem. In a specific region of parameters, a sequence of critical points is achieved exhibiting a unified cosmic evolution of the Universe starting from early inflation (represented by source point), which is followed by a decelerated intermediate phase (described by saddle solution), and finally goes through the late-time dark energy dominated Universe (represented by stable point). Finally, non-singular bouncing behavior of the Universe is also investigated for this model numerically.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"175 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2024-12-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142904830","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":"Exact regular black hole solutions with de Sitter cores and Hagedorn fluid","authors":"Vitalii Vertogradov and Ali Övgün","doi":"10.1088/1361-6382/ada082","DOIUrl":"https://doi.org/10.1088/1361-6382/ada082","url":null,"abstract":"In this paper, we present three exact solutions to the Einstein field equations, each illustrating different black hole models. The first solution introduces a black hole with a variable equation of state, , which can represent both singular and regular black holes depending on the parameters M0 and w0. The second solution features a black hole with Hagedorn fluid, relevant to the late stages of black hole formation, and reveals similarities to the first solution by also describing both singular and regular black holes in a specific case. Furthermore, we investigate the shadows cast by these black hole solutions to constrain their parameters. Recognizing that real astrophysical black holes are dynamic, we developed a third, dynamical solution that addresses gravitational collapse and suggests the potential formation of naked singularities. This indicates that a black hole can transition from regular to singular and back to regular during its evolution.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"65 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2024-12-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142905018","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":"Relativistic elastic membranes: rotating disks and Dyson spheres","authors":"Paulo Mourão, José Natário and Rodrigo Vicente","doi":"10.1088/1361-6382/ad9f16","DOIUrl":"https://doi.org/10.1088/1361-6382/ad9f16","url":null,"abstract":"We derive the equations of motion for relativistic elastic membranes, that is, two-dimensional elastic bodies whose internal energy depends only on their stretching, starting from a variational principle. We show how to obtain conserved quantities for the membrane’s motion in the presence of spacetime symmetries, determine the membrane’s longitudinal and transverse speeds of sound in isotropic states, and compute the coefficients of linear elasticity with respect to the relaxed configuration. We then use this formalism to discuss two physically interesting systems: a rigidly rotating elastic disk, widely discussed in the context of Ehrenfest’s paradox, and a Dyson sphere, that is, a spherical membrane in equilibrium in Schwarzschild’s spacetime, with the isotropic tangential pressure balancing the gravitational attraction. Surprisingly, although spherically symmetric perturbations of this system are linearly stable, the axi-symmetric dipolar mode is already unstable. This may be taken as a cautionary tale against misconstruing radial stability as true stability.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"72 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2024-12-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142905017","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":"Host galaxy demographics of individually detectable supermassive black-hole binaries with pulsar timing arrays","authors":"Katharine Cella, Stephen R Taylor and Luke Zoltan Kelley","doi":"10.1088/1361-6382/ad9131","DOIUrl":"https://doi.org/10.1088/1361-6382/ad9131","url":null,"abstract":"Massive black hole binaries (MBHBs) produce gravitational waves (GWs) that are detectable with pulsar timing arrays. We determine the properties of the host galaxies of simulated MBHBs at the time they are producing detectable GW signals. The population of MBHB systems we evaluate is from the Illustris cosmological simulations taken in tandem with post processing semi-analytic models of environmental factors in the evolution of binaries. Upon evolving to the GW frequency regime accessible by pulsar timing arrays, we calculate the detection probability of each system using a variety of different values for pulsar noise characteristics in a plausible near-future International Pulsar Timing Array dataset. We find that detectable systems have host galaxies that are clearly distinct from the overall binary population and from most galaxies in general. With conservative noise factors, we find that host stellar metallicity, for example, peaks at as opposed to the total population of galaxies which peaks at . Additionally, the most detectable systems are much brighter in magnitude and more red in color than the overall population, indicating their likely identity as large ellipticals with diminished star formation. These results can be used to develop effective search strategies for identifying host galaxies and electromagnetic counterparts following GW detection by pulsar timing arrays.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"34 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2024-12-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142901829","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":"Quantum-fluid correspondence in relativistic fluids with spin: from Madelung form to gravitational coupling","authors":"Naoki Sato","doi":"10.1088/1361-6382/ad9fcd","DOIUrl":"https://doi.org/10.1088/1361-6382/ad9fcd","url":null,"abstract":"This paper explores the quantum-fluid correspondence in a charged relativistic fluid with intrinsic spin. We begin by examining the nonrelativistic case, showing that the inclusion of spin introduces a quantum correction to the classical fluid energy. This correction, coupled with Maxwell’s equations, naturally leads to the Schrödinger equation in Madelung form. Building on this foundation, we extend the formalism to a relativistic perfect fluid, identifying the system’s stress-energy-momentum tensor. Our analysis reveals that the trace of the quantum correction to this tensor corresponds to the energy density of an oscillator, with its frequency determined by the vorticity of the spin motion. We then use the stress-energy-momentum tensor to establish the relationship between the Ricci scalar curvature, as dictated by the Einstein field equations, and the fluid density in a static, spherically symmetric configuration. Lastly, we generalize the Madelung transformation to compressible Navier–Stokes flows with vorticity and viscosity by developing a tailored Clebsch representation of the velocity field. This theoretical framework offers potential applications for studying fluid-like systems with internal rotational degrees of freedom, commonly encountered in astrophysical settings.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"41 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2024-12-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142901832","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":"Novel topological phenomena of timelike circular orbits for charged test particles","authors":"Xu Ye and Shao-Wen Wei","doi":"10.1088/1361-6382/ad9f14","DOIUrl":"https://doi.org/10.1088/1361-6382/ad9f14","url":null,"abstract":"The topological approach has recently been successfully employed to investigate timelike circular orbits (TCOs) for massive neutral test particles. The observed vanishing topological number implies that these TCOs occur in pairs. However, the behavior of charged test particles in this regard remains unexplored. To address this issue, our study focuses on examining the influence of particle charge on the topology of TCOs within a spherically symmetrical black hole spacetime holding a nonvanishing radial electric field. We consider four distinct cases based on the charges of the particle and the black hole: unlike strong charge, unlike weak charge, like weak charge, and like strong charge. For each case, we calculate the corresponding topological number. Our results reveal that when the charge is large enough, the topological number takes a value of -1 instead of 0, which differs from the neutral particle scenario. Consequently, in cases of small charges, the TCOs appear in pairs, whereas in cases of larger charges, an additional unstable TCO emerges. These findings shed light on the influence of the particle charge on the topological properties and number of TCOs.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"327 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2024-12-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142901834","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":"Effects of quantum corrections to Lorentzian vacuum transitions in the presence of gravity","authors":"H García-Compeán, J Hernández-Aguilar, D Mata-Pacheco and C Ramírez","doi":"10.1088/1361-6382/ad9fcc","DOIUrl":"https://doi.org/10.1088/1361-6382/ad9fcc","url":null,"abstract":"We present a study of the vacuum transition probabilities taking into account quantum corrections. We first introduce a general method that expands previous works employing the Lorentzian formalism of the Wheeler–De Witt equation by considering higher order terms in the semiclassical expansion. The method presented is applicable in principle to any model in the minisuperspace and up to any desired order in the quantum correction terms. Then, we apply this method to obtain analytical solutions for the probabilities up to second quantum corrections for homogeneous isotropic and anisotropic universes. We use the Friedmann–Lemaitre–Robertson–Walker metric with positive and zero curvature for the isotropic case and the Bianchi III and Kantowski–Sachs metrics for the anisotropic case. Interpreting the results as distribution probabilities of creating universes by vacuum decay with a given size, we found that the general behaviour is that considering up to the second quantum correction leads to an avoidance of the initial singularity. However, we show that this result can only be achieved for the isotropic Universe. Furthermore, we also study the effect of anisotropy on the transition probabilities.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"15 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2024-12-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142901835","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":"Observational constraints on generic models of non-minimal curvature-matter coupling","authors":"Anirban Chatterjee, Akshay Panda and Abhijit Bandyopadhyay","doi":"10.1088/1361-6382/ad9f18","DOIUrl":"https://doi.org/10.1088/1361-6382/ad9f18","url":null,"abstract":"We investigate two classes of non-minimally coupled curvature-matter models in the FLRW Universe with a perfect fluid and analyze their cosmological implications using Supernova Ia, observed Hubble data, and baryon acoustic oscillation measurements. Non-minimal coupling is introduced via an additional term in the Einstein–Hilbert action. To obtain observational constraints, we use an exponential-type fluid-pressure profile characterized by the dimensionless parameter k and parameterize as Rn with another dimensionless parameter n. Two additional parameters, α and β in the functional form of determine the coupling strength. We identify significant regions in the (n, k)-parameter space for fixed coupling strength values where non-minimally coupled models align with observed late-time cosmic evolution. Additionally, we explore and discuss features of energy transfer between the curvature and matter sectors using observational data.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"14 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2024-12-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142901831","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":"A new study of the Unruh effect","authors":"Robert Dickinson, Jeff Forshaw, Ross Jenkinson and Peter Millington","doi":"10.1088/1361-6382/ad9c12","DOIUrl":"https://doi.org/10.1088/1361-6382/ad9c12","url":null,"abstract":"We revisit the Unruh effect within a general framework based on direct, probability-level calculations. We rederive the transition rate of a uniformly accelerating Unruh–DeWitt monopole detector coupled to a massive scalar field, from both the perspective of an inertial (Minkowski) observer and an accelerating (Rindler) observer. We show that, for a measurement at a finite time after the initial state is prepared, the two perspectives give the same transition rate. We confirm that an inertial detector in a thermal bath of Minkowski particles responds differently to the accelerated detector (which perceives a thermal bath of Rindler particles), except in the case of a massless field where there is agreement at all times. Finally, new numerical results for the transition rate are presented and explained, highlighting the transient effects caused by forcing the field to initially be in the Minkowski vacuum state.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"145 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2024-12-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142887983","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":"Path integral derivation of the thermofield double state in causal diamonds","authors":"Abhijit Chakraborty, Carlos R Ordóñez and Gustavo Valdivia-Mera","doi":"10.1088/1361-6382/ad9e65","DOIUrl":"https://doi.org/10.1088/1361-6382/ad9e65","url":null,"abstract":"In this article, we adopt the framework developed by Laflamme (1989 Physica A 158 58–63) to analyze the path integral of a massless—conformally invariant—scalar field defined on a causal diamond (CD) of size 2α in 1+1 dimensions. By examining the Euclidean geometry of the CD, we establish that its structure is conformally related to the cylinder , where the Euclidean time coordinate τ has a periodicity of β. This property, along with the conformal symmetry of the fields, allows us to identify the connection between the thermofield double (TFD) state of CDs and the Euclidean path integral defined on the two disconnected manifolds of the cylinder. Furthermore, we demonstrate that the temperature of the TFD state, derived from the conditions in the Euclidean geometry and analytically calculated, coincides with the temperature of the CD known in the literature. This derivation highlights the universality of the connection between the Euclidean path integral formalism and the TFD state of the CD, as well as it further establishes CDs as a model that exhibits all desired properties of a system exhibiting the Unruh effect.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"72 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2024-12-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142888060","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}