Special Issue "Advances in Gravitational Research"

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A special issue of Galaxies (ISSN 2075-4434).

Deadline for manuscript submissions: closed (30 June 2015)

Special Issue Editor

Guest Editor
Prof. Dr. Lorenzo Iorio

Ministero dell' Istruzione, dell' Università e della Ricerca (M.I.U.R.)-Istruzione. Fellow of the Royal Astronomical Society (F.R.A.S.) Viale Unità di Italia 68, 70125, Bari (BA), Italy
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Interests: General relativity and gravitation; Classical general relativity; Post-Newtonian approximation, perturbation theory, related approximations; Observational cosmology; Mathematical and relativistic aspects of cosmology; Modified theories of gravity; Higher-dimensional gravity and other theories of gravity; Experimental studies of gravity; Experimental tests of gravitational theories; Geodesy and gravity; Harmonics of the gravity potential field; geopotential theory and determination; Satellite orbits; Orbit determination and improvement; Astrometry and reference systems; Ephemerides, almanacs, and calendars

Special Issue Information

Dear Colleagues,

Gravitation is one of the known fundamental interactions shaping the fabric of the natural world. Although we have been familiar with it since the remote past, our knowledge of it is far less accurate than that of electromagnetism and of the nuclear interactions because of its comparatively feebler intensity. To date, the General Theory of Relativity (GTR) represents the best theoretical description of gravitation at our disposal. As such, GTR is one of the pillars of our knowledge of Nature; intense experimental and observational scrutiny is required not only to gain an ever-increasing confidence about it, but also to explore the borders of the realm of its validity at different regimes ranging from the shortest distances to extragalactic scales. To this aim, a variety of different theoretical, experimental and observational approaches are required to extend the frontiers of our knowledge of the gravitational phenomena. What are the possibilities opened up by forthcoming space-based missions? What is the status of some long-lasting experimental endeavors aimed to test certain relativistic predictions? Are there some founded hopes to testing newly predicted gravitational effects in the near future in some suitable astronomical and astrophysical laboratories? Might observations collected in the past for various purposes hide some surprises? Do Earth-based laboratory experiments have nothing new to say about gravitation? What is the role of alternative models of the gravitational interaction? These are just some of the questions that the present special issue will try to address.

Prof. Dr. Lorenzo Iorio
Guest Editor

Submission

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. Papers will be published continuously (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as 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 refereed through a peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Galaxies is an international peer-reviewed Open Access quarterly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. For the first couple of issues the Article Processing Charge (APC) will be waived for well-prepared manuscripts. English correction and/or formatting fees of 250 CHF (Swiss Francs) will be charged in certain cases for those articles accepted for publication that require extensive additional formatting and/or English corrections.

Keywords

  • general relativity and gravitation
  • experimental studies of gravity
  • experimental tests of gravitational theories
  • classical general relativity
  • modified theories of gravity

Published Papers (8 papers)

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Research

Open AccessArticle The Flyby Anomaly in an Extended Whitehead’s Theory
Galaxies 2015, 3(3), 113-128; doi:10.3390/galaxies3030113
Received: 18 June 2015 / Revised: 23 July 2015 / Accepted: 24 July 2015 / Published: 30 July 2015
Cited by 2 | PDF Full-text (633 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, we consider an extended version of Whitehead’s theory of gravity in connection with the flyby anomaly. Whitehead’s theory is a linear approximation defined in a background Minkowski spacetime, which gives the same solutions as standard general relativity for the Schwarzschild
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In this paper, we consider an extended version of Whitehead’s theory of gravity in connection with the flyby anomaly. Whitehead’s theory is a linear approximation defined in a background Minkowski spacetime, which gives the same solutions as standard general relativity for the Schwarzschild and Kerr metrics cast in Kerr–Schild coordinates. For a long time and because it gives the same results for the three classical tests—perihelion advance, light bending and gravitational redshift—it was considered a viable alternative to general relativity, but as it is really a linear approximation, it fails in more stringent tests. The model considered in this paper is a formal generalization of Whitehead’s theory, including all possible bilinear forms. In the resulting theory, a circulating vector field of force in the low velocities’ approximation for a rotating planet is deduced, in addition to Newtonian gravity. This extra force gives rise to small variations in the asymptotic velocities of flybys around the Earth to be compared to the recently reported flyby anomaly. Full article
(This article belongs to the Special Issue Advances in Gravitational Research)
Figures

Open AccessArticle Quantum Corrected Non-Thermal Radiation Spectrum from the Tunnelling Mechanism
Galaxies 2015, 3(2), 103-112; doi:10.3390/galaxies3020103
Received: 9 February 2015 / Revised: 21 May 2015 / Accepted: 28 May 2015 / Published: 12 June 2015
Cited by 1 | PDF Full-text (252 KB) | HTML Full-text | XML Full-text
Abstract
The tunnelling mechanism is today considered a popular and widely used method in describing Hawking radiation. However, in relation to black hole (BH) emission, this mechanism is mostly used to obtain the Hawking temperature by comparing the probability of emission of an outgoing
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The tunnelling mechanism is today considered a popular and widely used method in describing Hawking radiation. However, in relation to black hole (BH) emission, this mechanism is mostly used to obtain the Hawking temperature by comparing the probability of emission of an outgoing particle with the Boltzmann factor. On the other hand, Banerjee and Majhi reformulated the tunnelling framework deriving a black body spectrum through the density matrix for the outgoing modes for both the Bose-Einstein distribution and the Fermi-Dirac distribution. In contrast, Parikh and Wilczek introduced a correction term performing an exact calculation of the action for a tunnelling spherically symmetric particle and, as a result, the probability of emission of an outgoing particle corresponds to a non-strictly thermal radiation spectrum. Recently, one of us (C. Corda) introduced a BH effective state and was able to obtain a non-strictly black body spectrum from the tunnelling mechanism corresponding to the probability of emission of an outgoing particle found by Parikh and Wilczek. The present work introduces the quantum corrected effective temperature and the corresponding quantum corrected effective metric is written using Hawking’s periodicity arguments. Thus, we obtain further corrections to the non-strictly thermal BH radiation spectrum as the final distributions take into account both the BH dynamical geometry during the emission of the particle and the quantum corrections to the semiclassical Hawking temperature. Full article
(This article belongs to the Special Issue Advances in Gravitational Research)
Open AccessArticle Sagnac Effect, Ring Lasers and Terrestrial Tests of Gravity
Galaxies 2015, 3(2), 84-102; doi:10.3390/galaxies3020084
Received: 2 March 2015 / Revised: 29 April 2015 / Accepted: 6 May 2015 / Published: 21 May 2015
Cited by 2 | PDF Full-text (460 KB) | HTML Full-text | XML Full-text
Abstract
Light can be used as a probe to explore the structure of space-time: this is usual in astrophysical and cosmological tests; however, it has been recently suggested that this can be done also in terrestrial laboratories. Namely, the Gyroscopes In General Relativity (GINGER)
[...] Read more.
Light can be used as a probe to explore the structure of space-time: this is usual in astrophysical and cosmological tests; however, it has been recently suggested that this can be done also in terrestrial laboratories. Namely, the Gyroscopes In General Relativity (GINGER) project aims at measuring post-Newtonian effects, such as the gravito-magnetic ones, in an Earth-based laboratory, by means of a ring laser array. Here, we first review the theoretical foundations of the Sagnac effect, on which ring lasers are based, and then, we study the Sagnac effect in a terrestrial laboratory, emphasizing the origin of the gravitational contributions that GINGER aims at measuring. Moreover, we show that accurate measurements allow one to set constraints on theories of gravity different from general relativity. Eventually, we describe the experimental setup of GINGER. Full article
(This article belongs to the Special Issue Advances in Gravitational Research)
Open AccessArticle Perspectives on Gravity-Induced Radiative Processes in Astrophysics
Galaxies 2015, 3(2), 72-83; doi:10.3390/galaxies3020072
Received: 9 February 2015 / Revised: 8 April 2015 / Accepted: 8 April 2015 / Published: 16 April 2015
Cited by 1 | PDF Full-text (324 KB) | HTML Full-text | XML Full-text
Abstract
Single-vertex Feynman diagrams represent the dominant contribution to physical processes, but are frequently forbidden kinematically. This is changed when the particles involved propagate in a gravitational background and acquire an effective mass. Procedures are introduced that allow the calculation of lowest order diagrams,
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Single-vertex Feynman diagrams represent the dominant contribution to physical processes, but are frequently forbidden kinematically. This is changed when the particles involved propagate in a gravitational background and acquire an effective mass. Procedures are introduced that allow the calculation of lowest order diagrams, their corresponding transition probabilities, emission powers and spectra to all orders in the metric deviation, for particles of any spin propagating in gravitational fields described by any metric. Physical properties of the “space-time medium” are also discussed. It is shown in particular that a small dissipation term in the particle wave equations can trigger a strong back-reaction that introduces resonances in the radiative process and affects the resulting gravitational background. Full article
(This article belongs to the Special Issue Advances in Gravitational Research)
Open AccessArticle Thermodynamic Relations for the Entropy and Temperature of Multi-Horizon Black Holes
Galaxies 2015, 3(1), 53-71; doi:10.3390/galaxies3010053
Received: 12 October 2014 / Revised: 26 January 2015 / Accepted: 28 January 2015 / Published: 2 February 2015
Cited by 8 | PDF Full-text (282 KB) | HTML Full-text | XML Full-text
Abstract
We present some entropy and temperature relations of multi-horizons, even including the “virtual” horizon. These relations are related to the product, division and sum of the entropy and temperature of multi-horizons. We obtain the additional thermodynamic relations of both static and rotating black
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We present some entropy and temperature relations of multi-horizons, even including the “virtual” horizon. These relations are related to the product, division and sum of the entropy and temperature of multi-horizons. We obtain the additional thermodynamic relations of both static and rotating black holes in three- and four-dimensional (A)dS spacetime. Especially, a new dimensionless, charge-independence and T+S+ = T_S_-like relation is presented. This relation does not depend on the mass, electric charge, angular momentum and cosmological constant, as it is always a constant. These relations lead us to obtaining some interesting thermodynamic bounds of entropy and temperature, including the Penrose inequality, which is the first geometrical inequality of black holes. Besides, based on these new relations, one can obtain the first law of thermodynamics and the Smarr relation for all horizons of a black hole. Full article
(This article belongs to the Special Issue Advances in Gravitational Research)
Open AccessArticle Nonlocal General Relativity
Galaxies 2015, 3(1), 1-17; doi:10.3390/galaxies3010001
Received: 4 November 2014 / Accepted: 11 December 2014 / Published: 26 December 2014
Cited by 6 | PDF Full-text (287 KB) | HTML Full-text | XML Full-text
Abstract
A brief account of the present status of the recent nonlocal generalization of Einstein’s theory of gravitation is presented. The main physical assumptions that underlie this theory are described. We clarify the physical meaning and significance of Weitzenböck’s torsion and emphasize its intimate
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A brief account of the present status of the recent nonlocal generalization of Einstein’s theory of gravitation is presented. The main physical assumptions that underlie this theory are described. We clarify the physical meaning and significance of Weitzenböck’s torsion and emphasize its intimate relationship with the gravitational field, characterized by the Riemannian curvature of spacetime. In this theory, nonlocality can simulate dark matter; in fact, in the Newtonian regime, we recover the phenomenological Tohline–Kuhn approach to modified gravity. To account for the observational data regarding dark matter,  nonlocality is associated with a characteristic length scale of order 1 kpc. The confrontation of nonlocal gravity with observation is briefly discussed. Full article
(This article belongs to the Special Issue Advances in Gravitational Research)
Open AccessArticle Constraints on Non-Standard Gravitomagnetism by the Anomalous Perihelion Precession of the Planets
Galaxies 2014, 2(4), 466-481; doi:10.3390/galaxies2040466
Received: 29 May 2014 / Revised: 15 September 2014 / Accepted: 17 September 2014 / Published: 29 September 2014
Cited by 10 | PDF Full-text (358 KB) | HTML Full-text | XML Full-text
Abstract
In 2008, a team of astronomers reported an anomalous retrograde precession of the perihelion of Saturn amounting to \(\Delta \dot{\omega}_{\mathrm{SATURN}}=-0.006(2)\) arcsec per century (arcsec cy\(^{-1}\)). This unexplained precession was obtained after taking into account all classical and relativistic effects in the context of
[...] Read more.
In 2008, a team of astronomers reported an anomalous retrograde precession of the perihelion of Saturn amounting to \(\Delta \dot{\omega}_{\mathrm{SATURN}}=-0.006(2)\) arcsec per century (arcsec cy\(^{-1}\)). This unexplained precession was obtained after taking into account all classical and relativistic effects in the context of the highly refined EPM2008 ephemerides. More recent analyzes have not confirmed this effect, but they have found similar discrepancies in other planets. Our objective in this paper is to discuss a non-standard model involving transversal gravitomagnetism generated by the Sun as a possible source of these potential anomalies, to be confirmed by further data analyses. In order to compute the Lense–Thirring perturbations induced by the suggested interaction, we should consider the orientation of the Sun's rotational axis in Carrington elements and the inclination of the planetary orbits with respect to the ecliptic plane. We find that an extra component of the gravitomagnetic field not predicted by General Relativity could explain the reported anomalies without conflicting with the Gravity Probe B experiment and the orbits of the geodynamics satellites. Full article
(This article belongs to the Special Issue Advances in Gravitational Research)
Figures

Open AccessArticle Orbital Motions and the Conservation-Law/Preferred-Frame α3 Parameter
Galaxies 2014, 2(4), 482-495; doi:10.3390/galaxies2040482
Received: 10 June 2014 / Revised: 12 September 2014 / Accepted: 12 September 2014 / Published: 29 September 2014
Cited by 3 | PDF Full-text (338 KB) | HTML Full-text | XML Full-text
Abstract
We analytically calculate some orbital effects induced by the Lorentz-invariance momentum-conservation parameterized post-Newtonian (PPN) parameter \(\alpha_3\) in a gravitationally bound binary system made of a primary orbited by a test particle. We neither restrict ourselves to any particular orbital configuration nor to specific
[...] Read more.
We analytically calculate some orbital effects induced by the Lorentz-invariance momentum-conservation parameterized post-Newtonian (PPN) parameter \(\alpha_3\) in a gravitationally bound binary system made of a primary orbited by a test particle. We neither restrict ourselves to any particular orbital configuration nor to specific orientations of the primary's spin axis \( {\hat{\psi}}\). We use our results to put preliminary upper bounds on \(\alpha_3\) in the weak-field regime by using the latest data from Solar System's planetary dynamics. By linearly combining the supplementary perihelion precessions \(\Delta\dot\varpi\) of the Earth, Mars and Saturn, determined by astronomers with the Ephemerides of Planets and the Moon (EPM) 2011 ephemerides for the general relativistic values of the PPN parameters \(\beta=\gamma=1\), we infer \(|\alpha_3|\lesssim 6\times 10^{-10}\). Our result is about three orders of magnitude better than the previous weak-field constraints existing in the literature and of the same order of magnitude of the constraint expected from the future BepiColombo mission to Mercury. It is, by construction, independent of the other preferred-frame PPN parameters \(\alpha_1,\alpha_2\), both preliminarily constrained down to a \(\approx 10^{-6}\) level. Future analyses should be performed by explicitly including \(\alpha_3\) and a selection of other PPN parameters in the models fitted by the astronomers to the observations and estimating them in dedicated covariance analyses. Full article
(This article belongs to the Special Issue Advances in Gravitational Research)

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