Article
Astronomy & Astrophysics
Hamid Shabani, Hooman Moradpour, Amir Hadi Ziaie
Summary: In this work, we studied the phase-space analysis of generalized Rastall gravity (GRG), which is a modification of the original version of Rastall gravity (RG). We found that GRG allows for a stable critical point corresponding to the late-time accelerated expansion of the Universe. By considering dark matter (DM) and an ultra-relativistic perfect fluid (radiation) as cosmic ingredients, we showed that the model exhibits a viable cosmic evolution sequence, transitioning from a radiation-dominated era to a DM-dominated era and finally reaching a late-time dark energy (DE)-dominated era. Additionally, taking into account the contribution of spatial curvature leads to a growing mode that is consistent with recent observations.
PHYSICS OF THE DARK UNIVERSE
(2022)
Article
Astronomy & Astrophysics
Masato Minamitsuji
Summary: The analysis shows that the difference between comoving curvature perturbations in the original and new frames on superhorizon scales is determined by a combination of time derivatives, intrinsic entropy perturbations of the scalar field, and their time derivatives. Comoving curvature perturbations can remain invariant under disformal transformations on superhorizon scales under certain conditions, while tensor perturbations can also remain disformally invariant if conserved over time in the original frame.
Article
Physics, Multidisciplinary
M. Ilyas, Aftab Ahmad, Fawad Khan, M. Wasif
Summary: In this paper, the authors investigate the effects of perfect fluid models and extended f(R, G, T) gravity on the flat Friedmann-Lematre-Robertson-Walker metric. They focus on exploring finite-time future singularities in late-time cosmic accelerating phases using specific f(R, G, T) models. The authors also consider the most recent estimated values for various parameters to examine the viability and bounds of the models induced by different energy conditions.
Article
Physics, Particles & Fields
Vittorio De Falco, Emmanuele Battista, Salvatore Capozziello, Mariafelicia De Laurentis
Summary: Static and spherically symmetric wormhole solutions can be reconstructed in the framework of curvature based Extended Theories of Gravity, with modified gravitational potentials resulting from the extensions of General Relativity. Observations can constrain possible wormhole solutions, and stable and traversable wormholes can serve as a direct probe for this class of Extended Theories of Gravity.
EUROPEAN PHYSICAL JOURNAL C
(2021)
Article
Astronomy & Astrophysics
Sebastian Garcia-Saenz
Summary: Our analysis shows that coupling between vector fields described by the generalized Proca class of theories and a gravitational sector defined by a scalar-tensor theory of the degenerate type leads to the loss of at least one constraint associated with the scalar-tensor sector.
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
Jhan N. Martinez, Jose F. Rodriguez, Yeinzon Rodriguez, Gabriel Gomez
Summary: The generalized SU(2) Proca theory is investigated for its physical properties at astrophysical scales, revealing particle-like solutions known as gauge boson stars. The t'Hooft-Polyakov magnetic monopole configuration emerges as a viable possibility for the static, asymptotically flat, and globally regular solutions. Analytical and numerical methods are used to obtain these solutions, finding new features such as negative effective energy density and imaginary effective charge regions. Additionally, equilibrium sequences and turning points indicate the existence of stable solutions absent in the Einstein-Yang-Mills case.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Astronomy & Astrophysics
Valerio Faraoni, Theo B. Franconnet
Summary: This article investigates a puzzle in the recent thermodynamics of scalar-tensor gravity, where general relativity is a zero-temperature equilibrium state and scalar-tensor gravity is the nonequilibrium configuration of an effective dissipative fluid. A stealth solution of Brans-Dicke gravity with constant positive temperature is shown to be analogous to a metastable state for the effective fluid and to suffer from an instability. The stability analysis utilizes a modified gravity version of the Bardeen-Ellis-Bruni-Hwang gauge-invariant formalism for cosmological perturbations. The metastable state is destroyed by tensor perturbations.
Article
Astronomy & Astrophysics
Justin C. Feng, Shinji Mukohyama, Sante Carloni
Summary: In this article, we develop the formalism for singular hypersurfaces and junction conditions in generalized coupling theories using a variational approach. We then examine the behavior of sharp matter density gradients in generalized coupling theories. Through a detailed example, we find that sharp boundaries do not generate singularities in the dynamical frame despite the presence of an auxiliary field.
Article
Astronomy & Astrophysics
Chong-Sun Chu, Hai-Siong Tan
Summary: We present a general method to derive the appropriate junction conditions for gravitational theories with higher-order derivative terms. By representing the Dirac delta distribution as a limit of classical functions, we handle more singular terms appropriately. We demonstrate our method with specific examples and refine the accuracy of previous results. We also discuss some applications.
Article
Physics, Multidisciplinary
S. Capozziello, G. Lambiase, A. Stabile, An. Stabile
Summary: The article discusses the frequency shift of photons generated by rotating gravitational sources in the framework of curvature-based Extended Theories of Gravity. By analyzing the process of photon exchange between Earth and a satellite using perturbative methods, a general relation to constrain the free parameters of gravitational theories is found. The Moon is suggested as a possible laboratory to test theories of gravity through future experiments based on other Solar System bodies.
EUROPEAN PHYSICAL JOURNAL PLUS
(2021)
Article
Astronomy & Astrophysics
Sanved Kolekar
Summary: We examine the generalised Bianchi identity, del E-a(ab) = 0, in a general class of gravity theories. We derive interesting identities related to the divergence of E-ab which are intimately connected to the diffeomorphism invariance property of such theories. The implications of these results are discussed.
GENERAL RELATIVITY AND GRAVITATION
(2022)
Article
Physics, Particles & Fields
Romuald A. Janik, Matti Jarvinen, Jacob Sonnenschein
Summary: In the context of theories with a first order phase transition, a general covariant description of coexisting phases separated by domain walls using an additional order parameter-like degree of freedom is proposed. In the case of a holographic Witten model with a confining and deconfined phase, the resulting model extends hydrodynamics and has a simple formulation in terms of a spacetime action with corresponding expressions for the energy-momentum tensor. The proposed description leads to simple analytic profiles of domain walls, including expressions for surface tension density, which agree nicely with holographic numerical solutions, despite the apparent complexity of those gravitational backgrounds.
JOURNAL OF HIGH ENERGY PHYSICS
(2021)
Article
Astronomy & Astrophysics
Oem Trivedi
Summary: Interest in cosmological singularities has grown with the discovery of late-time acceleration of the universe and dark energy. Recent work classified singularities into strong and weak types, and discussed the formation conditions of type V singularities in different cosmologies.
Article
Physics, Nuclear
Goutam Manna, Arijit Panda, Aninda Karmakar, Saibal Ray, Md. Rabiul Islam
Summary: The work aims to generate a general formalism of L(X)-gravity in the context of dark energy under the framework of K-essence emergent geometry with the DBI variety of action. The modified field equation has been constructed using the metric formalism in f(R), L(X)-gravity, incorporating the Friedmann equations of the FLRW type. The solution of the modified Friedmann equations for a specific choice of f(R), L(X) is consistent with the dark energy domination theory and the accelerating features.
Article
Astronomy & Astrophysics
Aleksander Lukasz Lenart, Giada Bargiacchi, Maria Giovanna Dainotti, Shigehiro Nagataki, Salvatore Capozziello
Summary: By studying high-redshift objects such as quasars, the value of the Hubble constant can be corrected, which can help resolve the current discrepancy between the cosmic microwave background radiation and the value obtained from Type Ia supernovae observations.
ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES
(2023)
Review
Physics, Multidisciplinary
Miguel A. S. Pinto, Tiberiu Harko, Francisco S. N. Lobo
Summary: In this work, the author explores the irreversibility thermodynamics of open systems and the potential of gravitationally generated particle production in modified gravity. Specifically, the author examines the scalar-tensor representation of f(R, T) gravity in which the non-conservation of the energy-momentum tensor leads to particle creation. The author derives and discusses the expressions for the particle creation rate, creation pressure, and entropy and temperature evolutions, and shows how these concepts can be applied to cosmological models.
Article
Physics, Mathematical
Salvatore Capozziello, Maurizio Capriolo, Gaetano Lambiase
Summary: The issue of defining gravitational energy in a given spatial region is still unresolved in General Relativity, except for particular cases of localized objects. In this study, we generalize the Einstein gravitational energy-momentum pseudotensor to non-local theories of gravity and consider analytic functions of the non-local integral operator ?(-1). By applying the Noether theorem to a gravitational Lagrangian invariant under infinitesimal rigid translations, we define a gravitational energy-momentum pseudotensor that transforms like a tensor under affine transformations. This pseudotensor, along with the energy-momentum complex, can be derived using the continuity equations considering gravitational and matter components, and their weak field limit is performed for astrophysical applications.
INTERNATIONAL JOURNAL OF GEOMETRIC METHODS IN MODERN PHYSICS
(2023)
Article
Astronomy & Astrophysics
S. Capozziello, S. Zare, D. F. Mota, H. Hassanabadi
Summary: In this study, the effects of a dark matter spike near the supermassive black hole in M87 (Virgo A galaxy) were investigated using the Bumblebee Gravity theory. The aim was to determine the impact of spontaneous Lorentz symmetry breaking on the horizon, ergo-region, and shadow of the Kerr Bumblebee black hole in the spike region. Dark matter distribution was incorporated into a Lorentz-violating spherically symmetric space-time, and the resulting solution was generalized to a Kerr Bumblebee black hole. The shapes of the shadow were examined based on observational data for the dark matter spike density and radius.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Astronomy & Astrophysics
Salvatore Capozziello, Maria Caruana, Jackson Levi Said, Joseph Sultana
Summary: Teleparallel geometry provides a theoretical framework where gravitational interaction is mediated by torsion rather than curvature. Teleparallel analogue of Horndeski gravity is an approach within this framework considering scalar-tensor theories. It is a more general formalism than the standard metric one, allowing for a wider range of teleparallel Horndeski gravity models. The article explores constraints on these models in terms of ghost and Laplacian instabilities and finds that a large class of models is physically viable.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Editorial Material
Physics, Multidisciplinary
S. Capozziello, V. G. Gurzadyan
EUROPEAN PHYSICAL JOURNAL PLUS
(2023)
Article
Astronomy & Astrophysics
Ana Rita Ribeiro, Daniele Vernieri, Francisco S. N. Lobo
Summary: General Relativity is successful for weak gravitational fields but fails at high energies, like the initial singularity. Quantum Gravity is expected to provide insights into this problem. Loop Quantum Cosmology offers an alternative scenario to the Big Bang, avoiding the singularity and predicting a collapse to expansion through a bounce. This study uses metric f(R) gravity to reproduce modified Friedmann equations in the context of modified loop quantum cosmologies.
Article
Astronomy & Astrophysics
Marcello Miranda, Daniele Vernieri, Salvatore Capozziello, Valerio Faraoni
Summary: The physical nature of Horndeski gravity is explained as a dissipative effective fluid in a new approach. Requiring the constitutive equations of a Newtonian fluid restricts the theory to two subclasses of viable Horndeski gravity. A linear stress-energy tensor of the Horndeski effective fluid is sufficient for gravitational waves to propagate at light speed, while other Horndeski theories correspond to exotic non-Newtonian effective fluids. The two linear Horndeski classes are further studied in the framework of first-order thermodynamics of viscous fluids.
GENERAL RELATIVITY AND GRAVITATION
(2023)
Review
Physics, Mathematical
Francisco S. N. Lobo
Summary: The hybrid metric-Palatini approach is a successful gravitational theory that combines the advantages of metric and Palatini versions and avoids some drawbacks. This article explores the formulation of this hybrid approach and its achievements in passing local tests and applications in astrophysics and cosmology.
INTERNATIONAL JOURNAL OF GEOMETRIC METHODS IN MODERN PHYSICS
(2023)
Review
Physics, Particles & Fields
Pierre Auclair, David Bacon, Tessa Baker, Tiago Barreiro, Nicola Bartolo, Enis Belgacem, Nicola Bellomo, Ido Ben-Dayan, Daniele Bertacca, Marc Besancon, Jose J. Blanco-Pillado, Diego Blas, Guillaume Boileau, Gianluca Calcagni, Robert Caldwell, Chiara Caprini, Carmelita Carbone, Chia-Feng Chang, Hsin-Yu Chen, Nelson Christensen, Sebastien Clesse, Denis Comelli, Giuseppe Congedo, Carlo Contaldi, Marco Crisostomi, Djuna Croon, Yanou Cui, Giulia Cusin, Daniel Cutting, Charles Dalang, Valerio De Luca, Walter Del Pozzo, Vincent Desjacques, Emanuela Dimastrogiovanni, Glauber C. Dorsch, Jose Maria Ezquiaga, Matteo Fasiello, Daniel G. Figueroa, Raphael Flauger, Gabriele Franciolini, Noemi Frusciante, Jacopo Fumagalli, Juan Garcia-Bellido, Oliver Gould, Daniel Holz, Laura Iacconi, Rajeev Kumar Jain, Alexander C. Jenkins, Ryusuke Jinno, Cristian Joana, Nikolaos Karnesis, Thomas Konstandin, Kazuya Koyama, Jonathan Kozaczuk, Sachiko Kuroyanagi, Danny Laghi, Marek Lewicki, Lucas Lombriser, Eric Madge, Michele Maggiore, Ameek Malhotra, Michele Mancarella, Vuk Mandic, Alberto Mangiagli, Sabino Matarrese, Anupam Mazumdar, Suvodip Mukherjee, Ilia Musco, Germano Nardini, Jose Miguel No, Theodoros Papanikolaou, Marco Peloso, Mauro Pieroni, Luigi Pilo, Alvise Raccanelli, Sebastien Renaux-Petel, Arianna I. Renzini, Angelo Ricciardone, Antonio Riotto, Joseph D. Romano, Rocco Rollo, Alberto Roper Pol, Ester Ruiz Morales, Mairi Sakellariadou, Ippocratis D. Saltas, Marco Scalisi, Kai Schmitz, Pedro Schwaller, Olga Sergijenko, Geraldine Servant, Peera Simakachorn, Lorenzo Sorbo, Lara Sousa, Lorenzo Speri, Daniele A. Steer, Nicola Tamanini, Gianmassimo Tasinato, Jesus Torrado, Caner Unal, Vincent Vennin, Daniele Vernieri, Filippo Vernizzi, Marta Volonteri, Jeremy M. Wachter, David Wands, Lukas T. Witkowski, Miguel Zumalacarregui, James Annis, Feanor Reuben Ares, Pedro P. Avelino, Anastasios Avgoustidis, Enrico Barausse, Alexander Bonilla, Camille Bonvin, Pasquale Bosso, Matteo Calabrese, Mesut Caliskan, Jose A. R. Cembranos, Mikael Chala, David Chernoff, Katy Clough, Alexander Criswell, Saurya Das, Antonio da Silva, Pratika Dayal, Valerie Domcke, Ruth Durrer, Richard Easther, Stephanie Escoffier, Sandrine Ferrans, Chris Fryer, Jonathan Gair, Chris Gordon, Martin Hendry, Mark Hindmarsh, Deanna C. Hooper, Eric Kajfasz, Joachim Kopp, Savvas M. Koushiappas, Utkarsh Kumar, Martin Kunz, Macarena Lagos, Marc Lilley, Joanes Lizarraga, Francisco S. N. Lobo, Azadeh Maleknejad, C. J. A. P. Martins, P. Daniel Meerburg, Renate Meyer, Jose Pedro Mimoso, Savvas Nesseris, Nelson Nunes, Vasilis Oikonomou, Giorgio Orlando, Ogan Ozsoy, Fabio Pacucci, Antonella Palmese, Antoine Petiteau, Lucas Pinol, Simon Portegies Zwart, Geraint Pratten, Tomislav Prokopec, John Quenby, Saeed Rastgoo, Diederik Roest, Kari Rummukainen, Carlo Schimd, Aurelia Secroun, Alberto Sesana, Carlos F. Sopuerta, Ismael Tereno, Andrew Tolley, Jon Urrestilla, Elias C. Vagenas, Jorinde van de Vis, Rien van de Weygaert, Barry Wardell, David J. Weir, Graham White, Bogumila Swiezewska, Valery I. Zhdanov
Summary: This publication provides an overview of the latest advancements in LISA cosmology, including theory and methods, and identifies new opportunities to probe the universe using gravitational-wave observations by LISA.
LIVING REVIEWS IN RELATIVITY
(2023)
Article
Astronomy & Astrophysics
Hoang Ky Nguyen, Francisco S. N. Lobo
Summary: This paper introduces the recently obtained special Buchdahl-inspired metric, with focuses on the construction of the Kruskal-Szekeres diagram and the emergence of wormholes. The study finds that the wormhole structure allows for the formation of closed timelike curves (CTCs).
Article
Astronomy & Astrophysics
Matteo Califano, Ivan de Martino, Daniele Vernieri, Salvatore Capozziello
Summary: We investigate four cosmological models that may solve the Hubble tension by considering different dark energy equation of state. By creating mock catalogs and extracting events associated with possible electromagnetic counterpart, we estimate the precision to which the Einstein Telescope can bound the cosmological parameters. Our results show that the uncertainty in the Hubble constant is always below 1%, potentially offering a solution to the Hubble tension. The accuracy on other cosmological parameters is comparable to current methods, except for the emergent dark energy model where the Einstein Telescope alone can significantly improve the limits.
Article
Astronomy & Astrophysics
Ester Piedipalumbo, Stefano Vignolo, Pasquale Feola, Salvatore Capozziello
Summary: In this study, we investigate the non-flat interacting quintessence cosmology within the framework of scalar-tensor gravity, where a scalar field interacts with dark matter. By employing the Noether Symmetry Approach, we obtain general exact solutions for cosmological equations and determine the scalar-field self-interaction potentials. The obtained solutions are capable of reproducing the accelerated expansion of the Universe and are consistent with various observational datasets, including the SNeIa Pantheon data, gamma ray bursts Hubble diagram, and direct measurements of the Hubble parameter.
PHYSICS OF THE DARK UNIVERSE
(2023)
Article
Physics, Particles & Fields
Spiros Cotsakis, Jose P. Mimoso, John Miritzis
Summary: We propose a new formulation of f(R) gravity, referred to as scalarized f(R) gravity, which incorporates the Legendre transform as a dynamic term. This results in a theory with second-order field equations that describe general relativity with a self-interacting scalar field, without the need for introducing conformal frames. We demonstrate that the quadratic version of scalarized f(R) gravity reduces to general relativity with a massive scalar field, and explore its implications for Friedmann cosmology. Our findings suggest that scalarized f(R) gravity may provide simplified descriptions for cosmological applications, while the proposed formulation offers a new perspective on the relationship between f(R) gravity and scalar-tensor theories.
EUROPEAN PHYSICAL JOURNAL C
(2023)
Article
Physics, Particles & Fields
Vittorio De Falco, Francesco Bajardi, Rocco D'Agostino, Micol Benetti, Salvatore Capozziello
Summary: Various astrophysical methods are used to detect possible deviations from General Relativity in this work. A class of f(R) gravity models, selected by the existence of Noether symmetries, is considered. The study determines static and spherically symmetric black hole solutions that encompass small departures from the Schwarzschild geometry. The proposed strategy of using ray-tracing technique and considering the Poynting-Robertson effect proves to be robust and efficient in investigating gravity and detecting small deviations from General Relativity.
EUROPEAN PHYSICAL JOURNAL C
(2023)