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
Multidisciplinary Sciences
Sergei V. Chervon, Igor V. Fomin
Summary: This study examines scalar-torsion gravity theories with exact solutions based on a physical type of potential for cosmological inflationary models involving the non-minimal coupling of a scalar field and torsion. Different inflationary dynamics and corresponding scalar field parameters are analyzed. This approach allows for the consideration of various physical potentials and types of scalar-torsion gravity theories in the realization of two stages of accelerated expansion in the universe. The correspondence between the proposed inflationary models and observational constraints on cosmological perturbation parameters is also explored.
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
Physics, Multidisciplinary
Xian Gao
Summary: The authors made a comprehensive classification of scalar monomials and covariant derivatives up to the third order, emphasizing their importance in effective field theory and exploring their complementarity; through systematic classification and derivation, a complete basis of monomials was derived with the potential for novel ghostfree Lagrangians; in addition, diagrammatic representations were developed to simplify the analysis process.
SCIENCE CHINA-PHYSICS MECHANICS & ASTRONOMY
(2021)
Article
Astronomy & Astrophysics
Hao-Jui Kuan, Jasbir Singh, Daniela D. Doneva, Stoytcho S. Yazadjiev, Kostas D. Kokkotas
Summary: Recent research has shown the existence of scalarized neutron star solutions in a class of tensor-multiscalar theories of gravity with a nontrivial target space metric, where the scalar charge is zero and the structure of the solutions is very complex. Up to three solutions can exist for a single neutron star, and stability changes occur at the maximum mass models.
Article
Astronomy & Astrophysics
Katsuki Aoki, Shinji Tsujikawa
Summary: In this study, we investigate the coupling between a 4-dimensional vector field Aμ and a vector quantity 7μ, which is expressed in terms of Aμ and the metric tensor gμν. We find an interacting Lagrangian of the form f(X)Aμ,7μ, where f is an arbitrary function of X = -(1/2)AμAμ, which belongs to a scheme of beyond generalized Proca theories. Applying this coupling to a static and spherically symmetric vacuum configuration, we obtain hairy black hole solutions with nonvanishing temporal and radial vector field profiles.
Article
Astronomy & Astrophysics
Jose Edgar Madriz Aguilar, A. Bernal, M. Montes, J. Zamarripa, E. Aceves
Summary: In this study, we investigate the gauge invariant scalar fluctuations of the metric in a non-perturbative framework for a newly introduced Higgs inflationary model based on a geometrical scalar-tensor theory of gravity. The Higgs inflaton field in this model originates from the Weyl scalar field of the background geometry. We find that the power spectrum of linear scalar fluctuations of the metric exhibits a nearly scale invariance. For certain model parameters, the values of the scalar spectral index n(s) and the scalar to tensor ratio r fit well with the Planck 2018 results. Additionally, we demonstrate that this model successfully avoids the trans-planckian problem.
PHYSICS OF THE DARK UNIVERSE
(2022)
Article
Astronomy & Astrophysics
David Benisty, Moshe M. Chaichian, Markku Oksanen
Summary: This passage studies the phenomenological implications of the Mimetic Tensor-Vector-Scalar theory (MiTeVeS). The theory extends the vector field model of mimetic dark matter by incorporating a scalar field, which is known to be ghost instability-free. When there is no interaction between the scalar field and the vector field, the obtained cosmological solution corresponds to the General Theory of Relativity (GR) with a minimally-coupled scalar field. However, introducing an interaction term between the scalar field and the vector field results in interesting dynamics.
PHYSICS OF THE DARK UNIVERSE
(2023)
Article
Astronomy & Astrophysics
Alessandro Casalino, Lorenzo Sebastiani
Summary: This paper investigates the perturbation theory of Regularized Lovelock Gravity on curved FLRW spacetime, deriving a general expression for the velocity of gravitational waves. Application of the theory to slow-roll inflation on flat FLRW background yields power spectra of scalar and tensor perturbations, and equations for inflation observable quantities.
PHYSICS OF THE DARK UNIVERSE
(2021)
Article
Physics, Particles & Fields
Oem Trivedi, Maxim Khlopov
Summary: The study of the true nature of dark energy is an exciting topic in cosmology. In this work, the authors investigate the existence of finite time singularities in scalar field dark energy models based on the RS-II Braneworld. The results show that these models can exhibit various types of singularities under certain initial conditions.
EUROPEAN PHYSICAL JOURNAL C
(2022)
Article
Astronomy & Astrophysics
Da Huang, Chao-Qiang Geng, Hao-Jui Kuan
Summary: Spontaneous scalarization in massive scalar-tensor theories introduces extra polarizations in gravitational waves, offering valuable probes into gravity theories. Self-coupling effects suppress scalarization magnitude and reduce gravitational wave signals' amplitude. Self-interacting effects are negligible in gravitational waveforms, resulting in characteristic inverse-chirp patterns observed on Earth. Detection of scalarization-induced gravitational waves may be possible with future detectors at a signal-to-noise ratio level of O(100).
CLASSICAL AND QUANTUM GRAVITY
(2021)
Article
Physics, Particles & Fields
Tiberiu Harko, Haidar Sheikhahmadi
Summary: The study focuses on a warm inflationary scenario where scalar field and radiation fluid evolve with distinct four velocities, leading to an anisotropic cosmological evolution. By formulating the basic equations and comparing theoretical predictions with observational data from the Planck satellite, constraints on free parameters are obtained. The functional forms of scalar field potentials compatible with non-comoving warm inflation are also obtained.
EUROPEAN PHYSICAL JOURNAL C
(2021)
Article
Astronomy & Astrophysics
R. R. Cuzinatto, E. M. de Morais, B. M. Pimentel
Summary: A scalar-tensor theory of gravity is presented on a torsion-free and metric compatible Lyra manifold, where a scale function defines the physical reference frame. The LyST gravity field equations have a well-defined Newtonian limit, showing the role of both metric and scale in describing gravitational interaction.
Article
Physics, Particles & Fields
Wompherdeiki Khyllep, Jibitesh Dutta
Summary: Non-minimal coupled scalar field models have various cosmological applications, such as describing dark energy, dark matter, and cosmic inflation. By utilizing bifurcation theory, these models can predict the global dynamics without fine-tuning of initial conditions, providing a more accurate description of cosmic evolution.
EUROPEAN PHYSICAL JOURNAL C
(2021)
Article
Physics, Nuclear
Tong-Zheng Wang, Wei-Liang Qian, Juan Fernando Zapata Zapata, Kai Lin
Summary: This study investigates the modes of scalar-tensor-Gauss-Bonnet theory black hole solutions and examines the characteristics of complex frequencies and the stability of the metric.
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)
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
Physics, Multidisciplinary
Stefano Camera, Salvatore Capozziello, Lorenzo Fatibene, Andrea Orizzonte
Summary: We investigate how the cosmological equation of state can be used to scrutinize extended theories of gravity, specifically the Palatini f(R) gravity. The effective equation of state produced by a given model is studied, and the inverse problem of determining which models are compatible with a given effective equation of state is also considered. We find that power-law models are capable of transforming barotropic Equations of State into effective barotropic ones, and the form of equation of state is preserved only for f(R) = R. Additionally, quadratic and non-homogeneous effective Equations of State contain the Starobinsky model and other models.
EUROPEAN PHYSICAL JOURNAL PLUS
(2023)
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)
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
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)
Article
Astronomy & Astrophysics
G. G. L. Nashed, S. Capozziello
Summary: This study investigates the possible modifications of general relativity at ultraviolet and infrared scales, particularly considering the possibility of parity violation in strong gravity regime. The Chern-Simons gravity theory is used to account for the parity violation. The study shows that for certain spacetime structures, Chern-Simons gravity is equivalent to general relativity, but it is not applicable to (A)dS-Kerr/Kerr black holes. The thermodynamic quantities and geodesic equation of the black hole are also calculated.
Article
Astronomy & Astrophysics
M. G. Dainotti, A. L. Lenart, A. Chraya, G. Sarracino, S. Nagataki, N. Fraija, S. Capozziello, M. Bogdan
Summary: Currently, there is a debate about cosmological models and their corresponding parameters due to the discrepancy between H-0 obtained from SNe Ia and the Planck data. Considering high redshift probes like gamma-ray bursts (GRBs) is necessary but challenging due to the large range of GRB luminosities. In this study, we use the 3D Dainotti fundamental plane relation to infer cosmological parameters, and by considering selection and evolutionary effects, we obtain a lower intrinsic scatter compared to previous results. Our analysis, using GRB correlations and complemented with SNe Ia and BAO measurements, confirms the parameters of the Lambda cold dark matter model but with the advantage of using probes detected up to z = 5.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
