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Universe
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Gravitational Radiation in Cosmological Spacetimes
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Gravitational Radiation in Cosmological Spacetimes

A special issue of Universe (ISSN 2218-1997). This special issue belongs to the section "Gravitation".

Deadline for manuscript submissions: closed (31 July 2022) | Viewed by 5764

Special Issue Editor

Dr. B.P. Bonga (Béatrice)

E-Mail Website
Guest Editor
Institute for Mathematics, Astrophysics and Particle Physics, Radboud University, 6525 AJ Nijmegen, The Netherlands
Interests: gravitational wave theory; resonance effects in neutron stars and black hole spacetimes; gravitational radiation in cosmological spacetimes; early universe cosmology
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Gravitational waves are now observed by LIGO-Virgo a few times a month, and it is difficult to imagine that in the early days of General Relativity, their physical reality was debated. However, many prominent scientists including Einstein himself questioned whether gravitational waves truly exist in nature. Theoretical developments to study gravitational waves generated by compact sources such as binary black holes in asymptotically flat spacetimes and the observation of the orbital decay in the Hulse–Taylor binary in the 1970s put an end to this debate. These theoretical advances also allowed the study of the nonlinear effects inherent in General Relativity by studying radiation at future null infinity. Despite these amazing advancements on the theoretical side, gravitational waves in cosmological spacetimes are still mostly studied in the linearized setting. With the increasing sensitivity of gravitational wave observatories, we will observe radiation emitted by sources increasingly far away, and therefore, cosmological effects will become important. Consequently, a fundamental understanding beyond geometrics optics approximation in the linearized setting is needed.

This Special Issue aims to collect and act as a catalyzer for progress in our understanding of gravitational waves emitted by compact sources in cosmological spacetimes—both with and without a cosmological constant.

Dr. B.P. Bonga (Béatrice)
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Universe is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • gravitational waves
  • cosmological constant
  • FLRW spacetimes
  • de Sitter spacetime
  • asymptotics
  • null infinity

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Published Papers (3 papers)

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Research

42 pages, 670 KiB  
Article
Gravitational Radiation at Infinity with Non-Negative Cosmological Constant
by José M. M. Senovilla
Universe 2022, 8(9), 478; https://doi.org/10.3390/universe8090478 - 12 Sep 2022
Cited by 8 | Viewed by 1511
Abstract
The existence of gravitational radiation arriving at null infinity J+, i.e., escaping from the physical system, is addressed in the presence of a non-negative cosmological constant Λ≥0. The case with vanishing Λ is well understood and relies on [...] Read more.
The existence of gravitational radiation arriving at null infinity J+, i.e., escaping from the physical system, is addressed in the presence of a non-negative cosmological constant Λ≥0. The case with vanishing Λ is well understood and relies on the properties of the News tensor field (or the News function) defined at J+. The situation is drastically different when Λ>0, where there is no known notion of ‘News’ with similar good properties. In this paper, both situations are considered jointly from a tidal point of view, that is, taking into account the strength (or energy) of the curvature tensors. The fundamental object used for this purposes is the asymptotic (radiant) super-momentum, a causal vector defined at infinity with remarkable properties. This leads to a novel characterization of gravitational radiation valid for the general case with Λ≥0, which has been proven to be equivalent when Λ=0 to the standard one based on News. Here, the implications of this result when Λ>0 are analyzed in detail. A general procedure to construct ‘News tensors’ when Λ>0 is depicted, a proposal for asymptotic symmetries is provided, and an example of a conserved charge that may detect gravitational radiation at J+ is exhibited. A series of illustrative examples is listed as well. Full article
(This article belongs to the Special Issue Gravitational Radiation in Cosmological Spacetimes)
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26 pages, 2981 KiB  
Article
Lensing Magnification Seen by Gravitational Wave Detectors
by Giulia Cusin, Ruth Durrer and Irina Dvorkin
Universe 2022, 8(1), 19; https://doi.org/10.3390/universe8010019 - 30 Dec 2021
Cited by 4 | Viewed by 1857
Abstract
In this paper, we studied the gravitational lensing of gravitational wave events. The probability that an observed gravitational wave source has been (de-)amplified by a given amount is a detector-dependent quantity which depends on different ingredients: the lens distribution, the underlying distribution of [...] Read more.
In this paper, we studied the gravitational lensing of gravitational wave events. The probability that an observed gravitational wave source has been (de-)amplified by a given amount is a detector-dependent quantity which depends on different ingredients: the lens distribution, the underlying distribution of sources and the detector sensitivity. The main objective of the present work was to introduce a semi-analytic approach to study the distribution of the magnification of a given source population observed with a given detector. The advantage of this approach is that each ingredient can be individually varied and tested. We computed the expected magnification as both a function of redshift and of the observedsource luminosity distance, which is the only quantity one can access via observation in the absence of an electromagnetic counterpart. As a case study, we then focus on the LIGO/Virgo network and on strong lensing (μ>1). Full article
(This article belongs to the Special Issue Gravitational Radiation in Cosmological Spacetimes)
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18 pages, 1559 KiB  
Article
Cherenkov Gravitational Radiation during the Radiation Era
by Yi-Zen Chu and Yen-Wei Liu
Universe 2021, 7(11), 437; https://doi.org/10.3390/universe7110437 - 15 Nov 2021
Cited by 1 | Viewed by 1790
Abstract
Cherenkov radiation may occur whenever the source is moving faster than the waves it generates. In a radiation dominated universe, with equation-of-state w=1/3, we have recently shown that the Bardeen scalar-metric perturbations contribute to the linearized Weyl tensor [...] Read more.
Cherenkov radiation may occur whenever the source is moving faster than the waves it generates. In a radiation dominated universe, with equation-of-state w=1/3, we have recently shown that the Bardeen scalar-metric perturbations contribute to the linearized Weyl tensor in such a manner that its wavefront propagates at acoustic speed w=1/3. In this work, we explicitly compute the shape of the Bardeen Cherenkov cone and wedge generated respectively by a supersonic point mass (approximating a primordial black hole) and a straight Nambu-Goto wire (approximating a cosmic string) moving perpendicular to its length. When the black hole or cosmic string is moving at ultra-relativistic speeds, we also calculate explicitly the sudden surge of scalar-metric induced tidal forces on a pair of test particles due to the passing Cherenkov shock wave. These forces can stretch or compress, depending on the orientation of the masses relative to the shock front’s normal. Full article
(This article belongs to the Special Issue Gravitational Radiation in Cosmological Spacetimes)
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