Article
Physics, Particles & Fields
Joao Luis Rosa, D. Bazeia, A. S. Lobao Jr
Summary: In this work, we study braneworld configurations in the scalar-tensor representation of the f (R, T) gravity theory in the presence of a Cuscuton term in the source field matter Lagrangian. We derive the scalar-tensor representation and obtain its equations of motion. We then investigate two different models for the source field in a flat braneworld model with one extra dimension for the general case of a f (R, T) theory. The solutions are obtained numerically due to the complexity of the field equations. The Cuscuton term effectively enhances the effect, increasing the height of the stability potential barrier and the depth of the minimum of the graviton zero-mode on the brane. Additionally, we examine the cases of F(R) + T and R + G (T), and demonstrate the essential role of the scalar field phi in the development of internal structure on the brane.
EUROPEAN PHYSICAL JOURNAL C
(2022)
Article
Physics, Mathematical
Beatrice Murorunkwere, Fidele Twagirayezu, Albert Munyeshyaka, Joseph Ntahompagaze, Abraham Ayirwanda
Summary: This paper revisits the equivalence between f(R) and scalar tensor theories and explores different f(R) models. The potentials V(phi) for each f(R) model are derived, focusing on the early Universe and the inflation epoch. The expressions for the spectral index n(s) and tensor-to-scalar ratio r are obtained using the slow-roll approximation approach. Numerical values associated with each f(R) model are determined, some of which are consistent with the Planck survey results and others fall within the suggested range by Planck data. The Klein-Gordon equations (KGEs) of each f(R) model are also constructed, and numerical solutions considering different values of free parameters and initial conditions are found, indicating a decrease in the scalar field in the late Universe.
INTERNATIONAL JOURNAL OF GEOMETRIC METHODS IN MODERN PHYSICS
(2022)
Article
Astronomy & Astrophysics
Tomohiro Inagaki, Masahiko Taniguchi
Summary: We study the quadrupole radiation of gravitational waves in F(R) modified gravity, which exhibits a massive scalar mode. The explicit expressions for the quadrupole radiation and energy current of the scalar mode in general F(R) gravity models are derived. Binary stars and bouncing stars are considered as astronomical sources, and the quadrupole radiation of scalar and tensor modes are calculated. Under spherically symmetric conditions, the scalar mode radiates, while the tensor modes do not. The mass of the scalar mode is estimated for typical energy scales, and the potential detection of the scalar mode in future gravitational wave observations is discussed.
Article
Astronomy & Astrophysics
P. J. Pompeia
Summary: The analysis of f(T, del(mu 1) T, . . . ,del(mu n) . . . del(mu 1) T) gravity in the Jordan and Einstein frames was presented. The equivalence with a scalar-multitensor theory was proved for systems with a regular Hessian matrix in both frames. Introducing an auxiliary tensor of the same order for each derivative reduced the differential equation for the tetrad field to second order, but led to a system of coupled equations for the auxiliary fields.
Article
Astronomy & Astrophysics
David Langlois, Karim Noui, Hugo Roussille
Summary: A novel and remarkably simple formulation of degenerate higher-order scalar-tensor (DHOST) theories is presented, which can be simplified to the usual Einstein-Hilbert term through disformal transformations. This classification of all quadratic DHOST theories becomes transparent in a geometric reformulation that applies also to scalar-tensor theories degenerate only in the unitary gauge.
Article
Astronomy & Astrophysics
Erik Jimenez-Vazquez, Miguel Alcubierre
Summary: We study the critical gravitational collapse of a massless scalar field nonminimally coupled to gravity and determine the values of critical amplitude, critical exponent, and echoing exponent. We find that the behavior is similar to that of a minimally coupled scalar field for small coupling, but becomes more violent and rich in high coupling. A special slicing condition is introduced to avoid gauge pathologies in the strong-coupling regime.
Article
Physics, Particles & Fields
Joao Luis Rosa, A. S. Lobao Jr, D. Bazeia
Summary: In this work, we studied braneworld models in generalized f(R, T) gravity theories and used the scalar-tensor representation theory. By introducing auxiliary fields and relating them to the source field, we analyzed four possibilities regarding compactification and asymmetry of the brane. We found that in certain models, the solutions of the auxiliary fields are significantly influenced by the source field, exhibiting different behaviors.
EUROPEAN PHYSICAL JOURNAL C
(2022)
Article
Physics, Particles & Fields
A. Capolupo, G. Lambiase, A. Stabile, An. Stabile
Summary: This study examines the virial theorem in the context of scalar tensor fourth order gravity in the Newtonian limit. It demonstrates that a specific class of this theory is not suitable for explaining the large fraction of dark matter needed to account for the flatness of galaxies' rotation curves observed experimentally.
EUROPEAN PHYSICAL JOURNAL C
(2021)
Article
Astronomy & Astrophysics
Kai Flathmann, Manuel Hohmann
Summary: In this article, we calculate the post-Newtonian limit of a general class of scalar-nonmetricity theories of gravity. Using the parametrized post-Newtonian formalism, we find that most theories in this class are indistinguishable from general relativity on the post-Newtonian level, except for a particular coupling between the scalar field and nonmetricity.
Article
Astronomy & Astrophysics
Cristian Erices, Pantelis Filis, Eleftherios Papantonopoulos
Summary: The study demonstrates the avoidance of the no-hair theorem in scalar-tensor theories with bimetric structure by introducing an electric charge, leading to black hole solutions with rich thermodynamic behavior. The interplay of stability and phase transitions between different black hole configurations resembles a solid-liquid-gas system, with an electric potential acting as pressure and a triple point where three phases coexist equally probable.
Article
Astronomy & Astrophysics
Rui-Hui Lin, Xiang-Hua Zhai
Summary: General relativity can be formulated equivalently with a non-Riemannian geometry involving a nonmetricity Q but vanishing curvature R and torsion T. Modification based on this description leads to f(Q) gravity. The application of f(Q) gravity to spherically symmetric configurations is explored, demonstrating effects on external and internal solutions of compact stars through different modifications.
Article
Physics, Particles & Fields
Joao Luis Rosa, Matheus A. Marques, Dionisio Bazeia, Francisco S. N. Lobo
Summary: This work investigates the stability of thick braneworld systems in the context of f(R,T) gravity, considering models with and without matter fields. It shows that gravitational sector is stable against small metric perturbations and the shape of the graviton zero-mode can develop internal structure under certain parameter choices.
EUROPEAN PHYSICAL JOURNAL C
(2021)
Article
Astronomy & Astrophysics
Jiaming Shi, Taotao Qiu
Summary: This paper discusses the possibility of enhancing the tensor-to-scalar ratio r under the scalar-tensor theory where inflation is nonminimally coupled to gravity, modifying the Trans-Planckian censorship conjecture condition. The modification allows for a large r similar to O(10(-3)) at the end of inflation without violating the TCC, potentially indicating an asymptotically safe period in the early Universe.
Article
Astronomy & Astrophysics
Bofeng Wu, Xin Zhang
Summary: The paper discusses the metric of the external gravitational field in f(R) gravity, provides the form of the metric for pointlike or ball-like sources, and derives the multipole expansion for the gyroscope, including various types of precession. In f(R) gravity, the correction part corresponds to the results in general relativity.
Article
Astronomy & Astrophysics
Georgios Antoniou, Caio F. B. Macedo, Ryan McManus, Thomas P. Sotiriou
Summary: The study investigates the radial stability of scalarized black-hole solutions and shows that Ricci coupling has a positive impact on their stability. In addition, it is found that Ricci coupling significantly reduces the region where hyperbolicity is lost in the equation governing linear, radial perturbations.
Editorial Material
Astronomy & Astrophysics
Matteo Luca Ruggiero
Article
Physics, Multidisciplinary
Angelo Tartaglia, Matteo Luca Ruggiero
Summary: This paper investigates the geometry of a charged mass with angular momentum, described by the Kerr-Newman solution of the Einstein equations. The peculiar symmetry of the system is usually explained in terms of the gravito-magnetic field generated by the angular momentum of the source, resulting in the generalized Sagnac effect. The study of the asymmetry in the times of flight of counter-rotating light beams along a circular trajectory reveals that this asymmetry is independent of the charge and Newton's constant, only associated with the symmetry produced by the gravitomagnetic field.
Article
Astronomy & Astrophysics
Angelo Tartaglia, Massimo Bassan, Lorenzo Casalino, Mariateresa Crosta, Mario Lattanzi, Enrico Lorenzini, David Lucchesi, Roberto Peron, Giuseppe Pucacco, Matteo Luca Ruggiero, Francesco Santoli, Pavol Valko, Alberto Vecchiato, Francesco Vespe, Massimo Visco
Summary: This passage proposes placing transponders and atomic clocks in at least three of the Lagrange points of the Sun-Earth pair to exploit the time of flight asymmetry of electromagnetic signals. The main objective of this detection is to use the gravito-magnetic field to detect the galactic dark halo and potentially discover related opportunities.
EXPERIMENTAL ASTRONOMY
(2021)
Article
Education, Scientific Disciplines
Matteo Luca Ruggiero
Summary: This paper discusses the basic features of gravitational waves science and the limitations of traditional approaches to gravitational wave physics, proposing the use of Fermi coordinates to introduce a gravitoelectromagnetic analogy as a more suitable teaching method.
AMERICAN JOURNAL OF PHYSICS
(2021)
Article
Astronomy & Astrophysics
Lorenzo Iorio, Matteo Luca Ruggiero
Summary: This paper focuses on the secular changes of orbital elements of a planet in the solar system determined by the magnetic-like part of a gravitational wave field. The total force acting on a test particle is made of gravito-electric and gravito-magnetic contributions, with the latter depending on the particle's velocity. The effects of gravito-magnetic force are found to be much smaller than gravito-electric ones in terms of orbital eccentricity orders.
INTERNATIONAL JOURNAL OF MODERN PHYSICS D
(2021)
Article
Astronomy & Astrophysics
Matteo Luca Ruggiero
Summary: The linear gravitoelectromagnetic approach converts Einstein's equations into Maxwell-like equations to explain gravitational effects in the solar system under weak-field and slow-motion approximation. The analogy allows for further examination of gravitoelectromagnetic fields in non-stationary conditions and their application in describing test particle motion similar to Lorentz-like force equations starting from known solutions of Einstein's equations.
Article
Engineering, Aerospace
Matteo Luca Ruggiero, Angelo Tartaglia, Lorenzo Casalino
Summary: This article investigates a relativistic positioning system where the coordinates of the users are determined by the proper times broadcasted by clocks in motion in spacetime, known as emission coordinates. The study shows that emission coordinates in flat spacetime can be defined using simple geometrical properties of geodesic triangles, and an analytic solution for the receiver coordinates is obtained.
ADVANCES IN SPACE RESEARCH
(2022)
Article
Astronomy & Astrophysics
Matteo Luca Ruggiero, Antonello Ortolan, Clive C. Speake
Summary: It is well known that the rotation curves of galaxies cannot be explained by Newtonian gravity in the absence of dark matter. Even in the weak-field approximation, there exist general relativistic effects without a Newtonian counterpart, such as gravitomagnetic effects, which may play a relevant role in understanding the impact of dark matter on galactic dynamics.
CLASSICAL AND QUANTUM GRAVITY
(2022)
Article
Astronomy & Astrophysics
Matteo Luca Ruggiero
Summary: The interaction between plane gravitational waves and test masses can be described using Fermi coordinates in the proper detector frame, involving gravitoelectric and gravitomagnetic fields. We calculate the displacements produced by gravitational waves up to second order in the distance parameter using this approach, and emphasize the significance of the gravitomagnetic contribution related to gravitational induction. Additionally, we demonstrate how this approach can be generalized to calculate displacements up to arbitrary order.
GENERAL RELATIVITY AND GRAVITATION
(2022)
Article
Astronomy & Astrophysics
Lorenzo Iorio, Matteo Luca Ruggiero
Summary: This study analytically calculates the effect of modified gravity models on the radial velocity of binary systems and specifically calculates the impact of the cosmological constant. The results show that the influence of the cosmological constant on the radial velocity of the Proxima/alpha Centauri AB binary system can be considered negligible.
Article
Astronomy & Astrophysics
Antonio Gallerati, Matteo Luca Ruggiero, Lorenzo Iorio
Summary: This paper examines the impact of the Standard Model Extension on the perturbation of radial velocity and suggests that suitable exoplanets' configurations and improvements in detection techniques may contribute to obtaining new constraints on the model parameters.
Article
Physics, Multidisciplinary
Matteo Luca Ruggiero
Summary: In this study, the authors utilize Fermi coordinates to analyze the interaction between a plane gravitational wave and a proper detector frame. They emphasize the analogy between the effects of the gravitational wave and the electromagnetic field, particularly in terms of a Lorentz-like force equation. The authors focus on the impact of the wave on time measurements and evaluate its magnitude. Additionally, they calculate the expression of the local spacetime metric in cylindrical coordinates and explore its relevance to the helicity-rotation coupling.
EUROPEAN PHYSICAL JOURNAL PLUS
(2023)
Article
Astronomy & Astrophysics
Davide Astesiano, Matteo Luca Ruggiero
Summary: In this study, the gravitoelectromagnetic approach is used to investigate the impact of general relativity on galactic dynamics under the weak-field and slow-motion approximation. Contrary to expectations, a specific class of solutions for the gravitomagnetic field is shown to introduce non-negligible corrections to the Newtonian velocity profile. The origin and interpretation of these corrections are discussed, and explicit applications to various galactic models are provided.
Article
Astronomy & Astrophysics
Davide Astesiano, Matteo Luca Ruggiero
Summary: This study explores disk galaxies within the framework of general relativity, investigating the potential corrections to the purely Newtonian approach even in the low energy limit. By considering both low energy expansion and exact solutions, the connection between these different approaches is clarified. The analysis focuses on two different limits - gravitomagnetic analogy and strong gravitomagnetism - which show corrections of the same order as the Newtonian terms. The findings suggest a geometrical origin for a certain amount of dark matter effects, explaining the observed flat velocity profile without the need for dark matter contributions.
Article
Astronomy & Astrophysics
Matteo Luca Ruggiero, Antonello Ortolan