Article
Physics, Particles & Fields
Joao Luis Rosa, D. A. Ferreira, Dionisio Bazeia, Francisco S. N. Lobo
Summary: The study focuses on 5-dimensional braneworld scenarios within the scalar-tensor representation of the generalized hybrid metric-Palatini gravitational theory. It shows that all models are stable against small fluctuations of the metric and that the gravitational zero mode profile can be controlled by the model's parameters, particularly in the presence of an additional scalar field.
EUROPEAN PHYSICAL JOURNAL C
(2021)
Article
Physics, Mathematical
Nisha Godani
Summary: The theory of Hybrid metric-Palatini gravity, proposed in 2012, explains both local and cosmological observations. In this paper, the theory is used to obtain charged traversable wormhole solutions and the results are compared for different cases.
INTERNATIONAL JOURNAL OF GEOMETRIC METHODS IN MODERN PHYSICS
(2023)
Article
Astronomy & Astrophysics
Merce Guerrero, Gonzalo J. Olmo, Diego Rubiera-Garcia
Summary: This study examines reflection-asymmetric thin-shell wormholes within Palatini f(R) gravity and establishes conditions for stable wormholes supported by positive-energy matter sources. It also identifies parameter subsets for positioning the shell radius above the event horizon but below the photon sphere. Additionally, it demonstrates the phenomenon of two photon spheres allowing observers to see double shadows due to the effective potential on each side of the wormhole.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Joao Luis Rosa
Summary: In this study, we investigate the existence of traversable wormhole solutions supported by double gravitational layer thin shells that satisfy the null energy condition throughout the entire spacetime. A new method is proposed to find these solutions by discarding certain junction conditions and utilizing a specific quadratic-linear form of the action. Unlike previous solutions obtained through scalar-tensor representation of the theory, the solutions derived in this work are more abundant and applicable to a wide range of metrics and actions.
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)
Article
Astronomy & Astrophysics
Dhong Yeon Cheong, Koichi Hamaguchi, Yoshiki Kanazawa, Sung Mook Lee, Natsumi Nagata, Seong Chan Park
Summary: In axion models, the problem of gravitational violation of the Peccei-Quinn (PQ) symmetry due to axionic wormholes is addressed by introducing a nonminimal coupling of the axion field to gravity. The solution to the quality problem is found in the Palatini formulation, where the requested lower bound of the nonminimal coupling is slightly higher than that in the metric formulation.
Article
Astronomy & Astrophysics
Minxi He, Yusuke Mikura, Yuichiro Tada
Summary: We extend the Higgs inflation to include non-minimal couplings between Higgs and both the metric-type and the Palatini-type Ricci scalars in hybrid metric-Palatini gravity. Our model realizes slow-roll inflation in the large-field regime with observationally favored predictions. We also explore the unitarity property of our model and discuss possible UV-extended theories to achieve a weakly-coupled effective field theory.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Astronomy & Astrophysics
Joao Luis Rosa, Francisco S. N. Lobo, Diego Rubiera-Garcia
Summary: This study explores cosmological sudden singularities in the dynamically equivalent scalar-tensor representation of generalized hybrid metric-Palatini gravity. The research shows that sudden singularities may appear in the fourth-order time derivative of the scale factor under certain assumptions, providing constraints on the occurrence of sudden singularities in our universe as measured from the Big Bang.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
J. Sadeghi, S. Noori Gashti, F. Darabi
Summary: In this paper, we investigate the cosmological implications of a hybrid combination of Einstein-Hilbert action with curvature scalar R and a function f (R) in Palatini gravity within the framework of inflationary scenario, based on the Swampland conjecture. We analyze the cosmological quantities and compare them with observational data, such as slow-roll parameter, scalar spectral index (ns), tensor-to-scalar ratio (rs), and assess the compatibility of the model with Planck observations by applying the Swampland conjecture to different plots.
PHYSICS OF THE DARK UNIVERSE
(2022)
Article
Astronomy & Astrophysics
Salvatore Capozziello, Nisha Godani
Summary: Non-local gravity is considered to obtain stable and traversable wormhole solutions. By studying the class of Non-local Integral Kernel Theories of Gravity, constraints for the null energy condition and field equations are derived. The main result is that non-local gravity contributions allow for the stability and traversability of the wormhole without the need for exotic matter.
Article
Astronomy & Astrophysics
Hamidreza Saiedi
Summary: In this study, the thermodynamic behavior of time-dependent wormhole geometries is investigated within the Palatini approach to modified f(R) theories of gravity. By redefining energy density and pressure, the continuity equation is satisfied, leading to the exploration of total entropy variation and the validity of the generalized second law of thermodynamics in relation to apparent and event horizons of evolving wormholes.
GENERAL RELATIVITY AND GRAVITATION
(2021)
Article
Astronomy & Astrophysics
Milko Estrada, C. R. Muniz
Summary: In this paper, new d-dimensional and asymptotically flat wormhole solutions are obtained by assuming a specific form of the energy density distribution. Constraints for the involved parameters are found to build those wormholes. The properties of the obtained solutions, including embedding diagrams as well as Weak and Null Energy Conditions (WEC and NEC), are studied and it is shown that the violations of these energy conditions become more pronounced with larger spacetime dimension.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Physics, Mathematical
Nisha Godani
Summary: This study focuses on traversable wormholes using three different gravity models. The research explores wormhole solutions, defining a shape function and examining stability and energy conditions for each model.
INTERNATIONAL JOURNAL OF GEOMETRIC METHODS IN MODERN PHYSICS
(2021)
Article
Astronomy & Astrophysics
J. McDonald
Summary: In comparison to the conventional metric formulation, reconsideration of unitarity violation in the electroweak vacuum under the Palatini formulation reveals that Higgs Inflation model does not violate unitarity at low energies. This suggests that Palatini Higgs Inflation may have a significant advantage over metric Higgs Inflation in terms of conservation of unitarity.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Konstantinos Dimopoulos, Alexandros Karam, Samuel Sanchez Lopez, Eemeli Tomberg
Summary: We propose a model of quintessential inflation in Palatini R2 gravity, where a scalar field with a simple exponential potential is coupled to gravity with a running non-minimal coupling. By studying the combination of the scalar sector and an ideal fluid, we investigate the cosmological evolution of the model from inflation to dark energy domination. Numerical scan over the parameter space reveals points that align with observations for both the inflationary CMB data and the late-time behavior.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Editorial Material
Physics, Particles & Fields
Gonzalo J. Olmo, P. J. Porfirio
Summary: It is claimed in [1] that the existence of a Pontryagin term in the action of the Einstein-Palatini gravity theory disproves the conclusions of [2], which state that only in the case of Lovelock gravity are the metric and metric-affine formulations of gravity equivalent. However, it is shown that the addition of a Pontryagin term (or any other D-divergence) only affects the boundary and does not change the field equations and their solutions, which are those of General Relativity in the Palatini formalism. Therefore, the example provided in [1] is not a valid counterexample to [2].
Article
Astronomy & Astrophysics
M. G. Dainotti, G. Bargiacchi, A. L. Lenart, S. Nagataki, S. Capozziello
Summary: Currently, the cold dark matter model along with a cosmological constant is the best representation of the universe. However, we lack information in the high-redshift region and the study of quasars up to z = 7.54 has provided important insights into the matter density parameter omega( M ). This demonstrates the reliability of quasars as standard cosmological candles.
ASTROPHYSICAL JOURNAL
(2023)
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
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
Maria Giovanna Dainotti, Giada Bargiacchi, Malgorzata Bogdan, Aleksander Lukasz Lenart, Kazunari Iwasaki, Salvatore Capozziello, Bing Zhang, Nissim Fraija
Summary: By combining high-redshift probes such as GRBs and QSOs with other observational data, it is shown that alternative cosmological models could potentially explain the discrepancy in the Hubble constant. This study uses data from GRBs and QSOs, and applies statistical methods to reduce uncertainties in the estimation of cosmological parameters.
ASTROPHYSICAL JOURNAL
(2023)
Article
Astronomy & Astrophysics
Salvatore Capozziello, Gamal G. L. Nashed
Summary: We derive a novel class of four-dimensional black hole solutions in Gauss-Bonnet gravity coupled with a scalar field in the presence of Maxwell electrodynamics. The choice of metric ansatz and the presence of the scalar field lead to the emergence of higher-order terms and the creation of monopoles in the metric potentials. The computed invariants associated with the black holes show soft singularities and the solutions exhibit multiple horizons depending on the spacetime.
CLASSICAL AND QUANTUM GRAVITY
(2023)
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
Physics, Particles & Fields
Marzieh Peyravi, Samira Nazifkar, Francisco S. N. Lobo, Kurosh Javidan
Summary: In this work, thick brane models in 4 + 1 dimensions generated by higher order field theory kinks were obtained. The confining effects of the scalar field on the brane were verified. New solutions with exponential and power-law tails in different topological sectors were found.
EUROPEAN PHYSICAL JOURNAL C
(2023)
