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Recent Advances in Gravity: A Themed Issue in Honor of...
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Recent Advances in Gravity: A Themed Issue in Honor of Prof. Jorge Pullin on His 60th Anniversary

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

Deadline for manuscript submissions: 31 December 2024 | Viewed by 7825

Special Issue Editor

Prof. Dr. Parampreet Singh

E-Mail Website
Guest Editor
Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803, USA
Interests: quantum gravity; quantum cosmology; early universe cosmology
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

This themed issue aims to bring together state-of-the-art research in classical, quantum, numerical and foundations aspects of gravity to honor Prof. Jorge Pullin for his 60th orbit around the Sun. Jorge Pullin is Horace Hearne Chair with the Department of Physics & Astronomy at Louisiana State University. During his long and dynamical career, Jorge has published more than 200 research papers and 3 books on loop quantum gravity and has worked in all areas of gravitational physics including classical and quantum aspects, theoretical and experimental elements, foundational aspects of quantum theory and numerical relativity. Jorge's exemplary service to the community includes being the founding editor of Physical Review X, managing editor of International Journal of Modern Physics D, and editorial board of Living Reviews in Relativity, and starting International Loop Quantum Gravity seminars which have been run regularly by Jorge since 2006. He has been awarded various honors including the Fellow of American Physical Society and the American Association of Advancement of Science.

This Special Issue is designed to highlight recent developments in the subfields of loop quantum gravity, numerical relativity and foundations of quantum mechanics and quantum gravity.

Prof. Dr. Parampreet Singh
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

  • loop quantum gravity
  • black holes
  • foundations of quantum mechanics
  • numerical relativity
  • problem of time

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Published Papers (5 papers)

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Research

19 pages, 712 KiB  
Article
The Operational Meaning of Total Energy of Isolated Systems in General Relativity
by Abhay Ashtekar and Simone Speziale
Universe 2024, 10(9), 367; https://doi.org/10.3390/universe10090367 - 11 Sep 2024
Viewed by 845
Abstract
We present thought experiments to measure the Arnowitt–Deser–Misner EADM and Bondi–Sachs energy EBS of isolated systems in general relativity. The expression of EBS used in the protocol is likely to have other applications. In particular, it is well-suited to be [...] Read more.
We present thought experiments to measure the Arnowitt–Deser–Misner EADM and Bondi–Sachs energy EBS of isolated systems in general relativity. The expression of EBS used in the protocol is likely to have other applications. In particular, it is well-suited to be promoted to an operator in non-perturbative loop quantum gravity. Full article
(This article belongs to the Special Issue Recent Advances in Gravity: A Themed Issue in Honor of Prof. Jorge Pullin on His 60th Anniversary)
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10 pages, 672 KiB  
Article
Comparing Numerical Relativity and Perturbation Theory Waveforms for a Non-Spinning Equal-Mass Binary
by Tousif Islam, Scott E. Field and Gaurav Khanna
Universe 2024, 10(1), 25; https://doi.org/10.3390/universe10010025 - 9 Jan 2024
Viewed by 1377
Abstract
Past studies have empirically demonstrated a surprising agreement between gravitational waveforms computed using adiabatic–driven–inspiral point–particle black hole perturbation theory (ppBHPT) and numerical relativity (NR) following a straightforward calibration step, sometimes referred to as α-β scaling. Specifically focusing on the quadrupole mode, [...] Read more.
Past studies have empirically demonstrated a surprising agreement between gravitational waveforms computed using adiabatic–driven–inspiral point–particle black hole perturbation theory (ppBHPT) and numerical relativity (NR) following a straightforward calibration step, sometimes referred to as α-β scaling. Specifically focusing on the quadrupole mode, this calibration technique necessitates only two time-independent parameters to scale the overall amplitude and time coordinate. In this article, part of a Special Issue, we investigate this scaling for non-spinning binaries at the equal-mass limit. Even without calibration, NR and ppBHPT waveforms exhibit an unexpected degree of similarity after accounting for different mass scale definitions. Post-calibration, good agreement between ppBHPT and NR waveforms extends nearly up to the point of the merger. We also assess the breakdown of the time-independent assumption of the scaling parameters, shedding light on current limitations and suggesting potential generalizations for the α-β scaling technique. Full article
(This article belongs to the Special Issue Recent Advances in Gravity: A Themed Issue in Honor of Prof. Jorge Pullin on His 60th Anniversary)
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14 pages, 2371 KiB  
Article
Hyperparameter Optimization of an hp-Greedy Reduced Basis for Gravitational Wave Surrogates
by Franco Cerino, J. Andrés Diaz-Pace, Emmanuel A. Tassone, Manuel Tiglio and Atuel Villegas
Universe 2024, 10(1), 6; https://doi.org/10.3390/universe10010006 - 23 Dec 2023
Viewed by 1549
Abstract
In a previous work, we introduced, in the context of gravitational wave science, an initial study on an automated domain-decomposition approach for a reduced basis through hp-greedy refinement. The approach constructs local reduced bases of lower dimensionality than global ones, with the same [...] Read more.
In a previous work, we introduced, in the context of gravitational wave science, an initial study on an automated domain-decomposition approach for a reduced basis through hp-greedy refinement. The approach constructs local reduced bases of lower dimensionality than global ones, with the same or higher accuracy. These “light” local bases should imply both faster evaluations when predicting new waveforms and faster data analysis, particularly faster statistical inference (the forward and inverse problems, respectively). In this approach, however, we have previously found important dependence on several hyperparameters, which do not appear in a global reduced basis. This naturally leads to the problem of hyperparameter optimization (HPO), which is the subject of this paper. Here, we compare the efficiency of the Bayesian approach against grid and random searches, which are two order of magnitude slower. Then, we tackle the problem of HPO through Bayesian optimization.We find that, for the cases studied here of gravitational waves from the collision of two spinning but non-precessing black holes, for the same accuracy, local hp-greedy reduced bases with HPO have a lower dimensionality of up to 4×, depending on the desired accuracy. This factor should directly translate into a parameter estimation speedup in the context of reduced order quadratures, for instance. Such acceleration might help in the near real-time requirements for electromagnetic counterparts of gravitational waves from compact binary coalescences. The code developed for this project is available open source from public repositories. This paper is an invited contribution to the Special Issue “Recent Advances in Gravity: A Themed Issue in Honor of Prof. Jorge Pullin on his 60th Anniversary”. Full article
(This article belongs to the Special Issue Recent Advances in Gravity: A Themed Issue in Honor of Prof. Jorge Pullin on His 60th Anniversary)
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26 pages, 1637 KiB  
Article
Uniform Asymptotic Approximation Method with Pöschl–Teller Potential
by Rui Pan, John Joseph Marchetta, Jamal Saeed, Gerald Cleaver, Bao-Fei Li, Anzhong Wang and Tao Zhu
Universe 2023, 9(11), 471; https://doi.org/10.3390/universe9110471 - 31 Oct 2023
Cited by 1 | Viewed by 1746
Abstract
In this paper, we study analytical approximate solutions for second-order homogeneous differential equations with the existence of only two turning points (but without poles) by using the uniform asymptotic approximation (UAA) method. To be more concrete, we consider the Pöschl–Teller (PT) potential, for [...] Read more.
In this paper, we study analytical approximate solutions for second-order homogeneous differential equations with the existence of only two turning points (but without poles) by using the uniform asymptotic approximation (UAA) method. To be more concrete, we consider the Pöschl–Teller (PT) potential, for which analytical solutions are known. Depending on the values of the parameters involved in the PT potential, we find that the upper bounds of the errors of the approximate solutions in general are ≲0.15∼10% for the first-order approximation of the UAA method. The approximations can be easily extended to high orders, for which the errors are expected to be much smaller. Such obtained analytical solutions can be used to study cosmological perturbations in the framework of quantum cosmology as well as quasi-normal modes of black holes. Full article
(This article belongs to the Special Issue Recent Advances in Gravity: A Themed Issue in Honor of Prof. Jorge Pullin on His 60th Anniversary)
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13 pages, 281 KiB  
Article
Diffeomorphism Covariance of the Canonical Barbero–Immirzi–Holst Triad Theory
by Donald Salisbury
Universe 2023, 9(11), 458; https://doi.org/10.3390/universe9110458 - 25 Oct 2023
Viewed by 1346
Abstract
The vanishing phase space generator of the full four-dimensional diffeomorphism-related symmetry group in the context of the Barbero–Immirz–Holst Lagrangian is derived directly, for the first time, from Noether’s second theorem. Its applicability in the construction of classical diffeomorphism invariants is reviewed. Full article
(This article belongs to the Special Issue Recent Advances in Gravity: A Themed Issue in Honor of Prof. Jorge Pullin on His 60th Anniversary)
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