Classical and Quantum Gravity最新文献

{"title":"On the evolution of the volume in Loop Quantum Cosmology","authors":"Beatriz Elizaga Navascués","doi":"10.1088/1361-6382/ad56ee","DOIUrl":"https://doi.org/10.1088/1361-6382/ad56ee","url":null,"abstract":"The dynamics of the expectation value of the volume is one of the key ingredients behind the replacement of the Big Bang singularity by a bounce in Loop Quantum Cosmology. As such, it is of great importance that this quantity is mathematically well-defined in the space of physical states of the theory. A number of caveats have been raised about such a definition entering in conflict with the quantum evolution of states, motivated by the situation found in quantum geometrodynamics. We show that there are ways around these caveats, all of which are related to the existence of quantization prescriptions leading to a nondegenerate curvature operator in Loop Quantum Cosmology. Interestingly, the properties of the curvature operator that may allow for a good behavior of the volume are only possible thanks to the discreteness of the geometry characteristic of the loop quantization procedure.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141444926","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 Einstein–Hilbert action for entropically dominant causal sets","authors":"Peter Carlip, Steve Carlip and Sumati Surya","doi":"10.1088/1361-6382/ad506e","DOIUrl":"https://doi.org/10.1088/1361-6382/ad506e","url":null,"abstract":"In the path integral formulation of causal set quantum gravity, the quantum partition function is a phase-weighted sum over locally finite partially ordered sets, which are viewed as discrete quantum spacetimes. It is known, however, that the number of ‘layered’ sets—a class of causal sets that look nothing like spacetime manifolds—grows superexponentially with the cardinality n, giving an entropic contribution that can potentially dominate that of the action. We show here that in any dimension, the discrete Einstein–Hilbert action for a typical K-layered causal set reduces to the simple link action to leading order in n. Combined with earlier work, this completes the proof that the layered sets, although entropically dominant, are very strongly suppressed in the path sum of causal set quantum gravity whenever the discreteness scale is greater than or equal to a (mildly dimension-dependent) order one multiple of the Planck scale.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141444796","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":"High-frequency solutions to the Einstein equations","authors":"Cécile Huneau and Jonathan Luk","doi":"10.1088/1361-6382/ad5487","DOIUrl":"https://doi.org/10.1088/1361-6382/ad5487","url":null,"abstract":"We review recent mathematical results concerning the high-frequency solutions to the Einstein vacuum equations and the limits of these solutions. In particular, we focus on two conjectures of Burnett, which attempt to give an exact characterization of high-frequency limits of vacuum spacetimes as solutions to the Einstein–massless Vlasov system. Some open problems and future directions are discussed.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141430391","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":"Automated evaluation of environmental coupling for Advanced LIGO gravitational wave detections","authors":"A F Helmling-Cornell, P Nguyen, R M S Schofield and R Frey","doi":"10.1088/1361-6382/ad5139","DOIUrl":"https://doi.org/10.1088/1361-6382/ad5139","url":null,"abstract":"The extreme sensitivity required for direct observation of gravitational waves by the Advanced LIGO detectors means that environmental noise is increasingly likely to contaminate Advanced LIGO gravitational wave signals if left unaddressed. Consequently, environmental monitoring efforts have been undertaken and novel noise mitigation techniques have been developed which have reduced environmental coupling and made it possible to analyze environmental artifacts with potential to affect the 90 gravitational wave events detected from 2015–2020 by the Advanced LIGO detectors. So far, there is no evidence for environmental contamination in gravitational wave detections. However, automated, rapid ways to monitor and assess the degree of environmental coupling between gravitational wave detectors and their surroundings are needed as the rate of detections continues to increase. We introduce a computational tool, PEMcheck, for quantifying the degree of environmental coupling present in gravitational wave signals using data from the extant collection of environmental monitoring sensors at each detector. We study its performance when applied to 79 gravitational waves detected in LIGO’s third observing run and test its performance in the case of extreme environmental contamination of gravitational wave data. We find that PEMcheck’s automated analysis identifies only a small number of gravitational waves that merit further study by environmental noise experts due to possible contamination, a substantial improvement over the manual vetting that occurred for every gravitational wave candidate in the first two observing runs. Building on a first attempt at automating environmental coupling assessments used in the third observing run, this tool represents an improvement in accuracy and interpretability of coupling assessments, reducing the time needed to validate gravitational wave candidates. With the validation provided herein; PEMcheck will play a critical role in event validation during LIGO’s fourth observing run as an integral part of the data quality report produced for each gravitational wave candidate.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141430569","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":"Probing primordial black hole scenarios with terrestrial gravitational wave detectors","authors":"Guillem Domènech and Misao Sasaki","doi":"10.1088/1361-6382/ad5488","DOIUrl":"https://doi.org/10.1088/1361-6382/ad5488","url":null,"abstract":"It is possible that primordial black holes (PBHs) constitute (or constituted) a significant fraction of the energy budget of our Universe. Terrestrial gravitational wave detectors offer the opportunity to test the existence of PBHs in two different mass ranges, from to . The first mass window is open via induced gravitational waves, and the second one is by gravitational waves from binary mergers. In this review, we outline and explain the different gravitational wave signatures of PBHs that may be probed by terrestrial gravitational wave detectors, such as the current LIGO/Virgo/KAGRA and future ones like Einstein Telescope and Cosmic Explorer. We mainly focus on the associated Gravitational Wave background signals and provide rough estimates for their typical frequency and amplitude. We also discuss complementary probes for these PBH mass ranges.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-06-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141425472","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":"Impact of energy–momentum conservation violation on the configuration of compact stars and their GW echoes","authors":"Jyatsnasree Bora, Dhruba Jyoti Gogoi, S K Maurya and Ghulam Mustafa","doi":"10.1088/1361-6382/ad51c4","DOIUrl":"https://doi.org/10.1088/1361-6382/ad51c4","url":null,"abstract":"This work investigates the impacts of energy–momentum conservation violation on the configuration of strange stars constraint with gravitational wave (GW) event GW190814 as well as eight recent observations of compact objects. The GW echoes from these interesting classes of compact objects are also calculated. To describe the matter of strange stars, we have used two different equations of state (EoSs): first an ad-hoc exotic EoS, the stiffer MIT Bag model and next realistic CFL phase of quark matter EoS. We choose Rastall gravity as a simple model with energy–momentum conservation violation with a set of model parameter values. Our results show that this gravity theory permits stable solutions of strange stars and the resulting structures can foster GW echoes. We illustrate the implication of the gravity theory and found that the negative values of the Rastall parameter result in more compact stellar configurations and lower GW echo frequency. With an increase in the Rastall parameter, both the compactness of the stellar configurations and echo time decrease. It is worth mentioning here that with the chosen set of some probable strange star candidates from observational data and also in light of GW 190814, we have evaluated the radii of stellar models. Also, the GW echo frequencies associated with strange stars are found to be in the range of 9–27 kHz for both cases. From this work, it is also inferred that the assumption regarding the equivalence of Rastall’s theory to Einstein’s theory is refuted as we have noticed many deviations in the physical properties of the considered compact stars.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-06-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141333761","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":"Casimir wormholes in Brans–Dicke theory","authors":"Amir Hadi Ziaie and Mohammad Reza Mehdizadeh","doi":"10.1088/1361-6382/ad5136","DOIUrl":"https://doi.org/10.1088/1361-6382/ad5136","url":null,"abstract":"In recent years there has been a growing interest in the field of wormhole physics in the presence of Casimir effect. As this effect provides negative energy density, it can be utilized as an ideal candidate for the exotic matter required for creating a traversable wormhole. In the context of modified theories of gravity such as Brans–Dicke (BD) theory (Brans and Dicke 1961 Phys. Rev.124 925), wormhole geometries have been vastly investigated. However, the scientific literature is silent on the issue of BD wormholes in the presence of Casimir energy. Our aim in the present study is to seek for static spherically symmetric solutions representing wormhole configurations in BD theory with Casimir energy as the supporting matter. The Casimir setup we assume comprises two electrically neutral, infinitely large parallel planes placed in a vacuum. We then consider the Casimir vacuum energy density of a scalar field in such a configuration with Dirichlet and mixed boundary conditions. In the former case the corresponding Casimir force is attractive and in the latter this force is repulsive. We present exact zero tidal force wormhole solutions as well as those with non vanishing redshift function for both types of Casimir energies. The conditions on wormhole solutions along with the weak (WEC) and null (NEC) energy conditions put constraints on the values of BD coupling parameter. These constraints are also subject to the value of BD scalar field at the throat and the throat radius. We therefore find that BD wormholes in the presence of Casimir energy can exist without violating NEC and WEC (for the repulsive Casimir force). Finally, we examine the equilibrium condition for stability of the obtained solutions using Tolman–Oppenheimer–Volkoff equation.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-06-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141319908","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":"Cosmological higher-curvature gravities","authors":"Javier Moreno and Ángel J Murcia","doi":"10.1088/1361-6382/ad51c5","DOIUrl":"https://doi.org/10.1088/1361-6382/ad51c5","url":null,"abstract":"We examine higher-curvature gravities whose Friedmann–Lemaître–Robertson–Walker configurations are specified by equations of motion which are of second order in derivatives, just like in Einstein gravity. We name these theories Cosmological Gravities and initiate a systematic exploration in dimensions . First, we derive an instance of Cosmological Gravity to all curvature orders and dimensions . Second, we study Cosmological Gravities admitting non-hairy generalizations of the Schwarzschild solution characterized by a single function whose equation of motion is, at most, of second order in derivatives. We present explicit instances of such theories for all curvature orders and dimensions . Finally, we investigate the equations of motion for cosmological perturbations in the context of generic Cosmological Gravities. Remarkably, we find that the linearized equations of motion for scalar cosmological perturbations in any Cosmological Gravity in contain no more than two time derivatives. We explicitly corroborate this aspect by presenting the equations for the scalar perturbations in some four-dimensional Cosmological Gravities up to fifth order in the curvature.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-06-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141309154","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":"Searches for compact binary coalescence events using neural networks in LIGO/Virgo third observation period","authors":"A Menéndez-Vázquez, M Andrés-Carcasona, M Martínez and Ll M Mir","doi":"10.1088/1361-6382/ad4f42","DOIUrl":"https://doi.org/10.1088/1361-6382/ad4f42","url":null,"abstract":"We present the results on the search for the coalescence of compact binary mergers using convolutional neural networks (CNNs) and the LIGO/Virgo data for the O3 observation period. Two-dimensional images in time and frequency are used as input. The analysis is performed in three separate mass regions covering the range for the masses in the binary system from 0.2 M to 100 M , excluding very asymmetric mass configurations. We explore neural networks trained with input information from pairs of interferometers or all three interferometers together, concluding that the use of the maximum information available leads to an improved performance. A scan over the O3 data set, using the CNNs, is performed with different false rate thresholds for claiming detection of at most one event per year or at most one event per week. The latter would correspond to a loose online selection still leading to affordable false alarm rates. The efficiency of the neutral networks to detect the O3 catalog events is discussed. In the case of a false rate threshold of at most one event per week, the scan leads to the detection of about 50% of the O3 catalog events. Once the search is limited to the catalog events within the mass range used for neural networks training, the detection efficiency increases up to 70 . Further improvement in search efficiency, using the same type of algorithms, will require the implementation of new criteria to suppress the remaining major background sources.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-06-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141309046","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 transformation of the rotational energy of a Kerr black hole","authors":"Shu-Rui Zhang and Mikalai Prakapenia","doi":"10.1088/1361-6382/ad51c2","DOIUrl":"https://doi.org/10.1088/1361-6382/ad51c2","url":null,"abstract":"This paper analyzes the feedback of the rotational energy extraction from a Kerr black hole (BH) by the ‘ballistic method’, i.e. the test particle decay in the BH ergosphere pioneered by Roger Penrose. The focus is on the negative energy counterrotating particles (which can be massive or massless) going in towards the horizon, and the feedback on the BH irreducible mass is assessed. Generally, the change in irreducible mass is a function of the conserved quantities of the particle. For an extreme Kerr BH and in the limit , all the reduced transformable energy goes into the irreducible mass (i.e. ), resulting in high irreversibility. The amount of extracted energy from the BH using test particles is much lower than the change of transformable energy. For non-extreme Kerr BHs, the effective potential of particle motion on the equatorial plane in Kerr spacetime is analyzed, and it is demonstrated that the Penrose process can only be undergone by BHs with a dimensionless spin if the decay point coincides with the turning point. Based on that, the lower limit of the change in irreducible mass is provided as a function of the dimensionless spin of the BH. The significance of the increase in the irreducible mass of the BH during the energy extraction process is generally and concisely illustrated by introducing the concept of transformable energy of the BH. The feedback from the Penrose process on the irreducible mass demonstrates the irreversibility of energy extraction and highlights that the total amount of energy that can be extracted from a BH is less than previously anticipated.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-06-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141308959","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}