Article
Physics, Multidisciplinary
J. K. Singh, Kazuharu Shaily, Kazuharu Bamba
Summary: In this paper, a bouncing cosmological scenario is studied in a specific flat FLRW model using a parameterized hyperbolic form of scale factor. The model is discussed in the f(R, G) formalism, where the proposed functional form of the Hubble parameter satisfies the bouncing criteria and avoids the initial singularity. The physical consequences of the model are discussed, including the crossing of the EoS parameter through the quintom line near the bouncing point.
CHINESE JOURNAL OF PHYSICS
(2023)
Article
Astronomy & Astrophysics
Santosh V. Lohakare, Francisco Tello-Ortiz, S. K. Tripathy, B. Mishra
Summary: In this paper, the bouncing behavior of cosmological models in the background of the Hubble function in the F(R,G) theory of gravity was studied. It was found that both models satisfy the bouncing cosmological properties and exhibit accelerating behavior at the late evolution time. The results of this study are of great significance for understanding cosmic evolution and solving cosmological problems.
Article
Astronomy & Astrophysics
Miguel A. Garcia-Aspeitia, A. Hernandez-Almada
Summary: The study revisits the Einstein-Gauss-Bonnet model, providing additional evidence for its pros and cons from a cosmological perspective. Results suggest that the acceleration parameter alpha of the EGB model is constrained in background cosmology, and the universe evolution seems to be always in an accelerated state.
PHYSICS OF THE DARK UNIVERSE
(2021)
Article
Astronomy & Astrophysics
Konstantinos F. Dialektopoulos, Jackson Levi Said, Zinovia Oikonomopoulou
Summary: In this work, the dynamical system phase space of Einstein-Gauss-Bonnet theory in cosmological minisuperspace is explored in the context of GW170817. The main features of the theory are bound together through a system of autonomous differential equations in the background of a flat Friedmann-Lemaitre-Robertson-Walker spacetime. The stability criteria of the critical points in this system are analyzed. The phase space of this scalar-tensor gravity is rich due to the fourth-order contributions of the Gauss-Bonnet invariant and the second order contribution of the scalar field together with their coupling dynamics. Additional critical points are found compared to previous works, which may be important for understanding the larger evolution of standard background cosmology within this class of gravitational models.
PHYSICS OF THE DARK UNIVERSE
(2023)
Article
Physics, Multidisciplinary
Ambuj Kumar Mishra, Shweta, Umesh Kumar Sharma
Summary: In this paper, wormholes in 4D Einstein-Gauss-Bonnet gravity are investigated without the need for exotic matter. The results show that the negative branch wormhole solutions satisfy the null energy conditions (NEC) throughout the entire space-time, while the positive branch reduces exactly to Morris-Thorne of GR.
PRAMANA-JOURNAL OF PHYSICS
(2022)
Article
Astronomy & Astrophysics
Hai-Shan Liu, H. Lu, Zi-Yu Tang, Bin Wang
Summary: A higher-derivative gravity theory is proposed, as an extension of the Starobinsky model, which introduces new black holes carrying massive scalar hair. These black holes are found to act as walls separating naked spacetime singularities and wormholes, with the entropy and temperature being the same for both the new hairy black hole and the Schwarzschild black hole at the same mass.
Article
Astronomy & Astrophysics
Eugeny Babichev, William T. Emond, Sabir Ramazanov
Summary: We study black holes in a modified gravity scenario involving a scalar field quadratically coupled to the Gauss-Bonnet invariant. The nonminimal coupling to gravity leads to symmetry restoration near the black hole horizon, prompting the development of the scalar wall in its vicinity. The model is fully consistent with the existence of an inflationary stage and predicts the speed of gravitational waves to be extremely close to unity.
Article
Astronomy & Astrophysics
M. Bousder, M. Bennai
Summary: This study investigates the charge of the 4D-Einstein-Gauss-Bonnet black hole by examining the charge of a particle-antiparticle pair at r(-) and r(+) horizons, showing the existence of two types of Schwarzschild black holes and quantified values for the Einstein-Gauss-Bonnet black hole charge. The study also reveals the Hawking-Bekenstein formula with two logarithmic corrections, where the second correction depends on the cosmological constant and the black hole charge. Finally, the thermodynamics of the EGB-AdS black hole is explored.
Article
Astronomy & Astrophysics
D. Jackson, R. Bufalo
Summary: In this work, the improved Deser-Woodard non-local gravity over five different cosmological models is analyzed, aiming to avoid the initial singular state of the universe. The numerical solution for the non-local distortion function is developed using the reconstruction procedure, providing viable cosmological solutions. The physical aspects and outcomes of the distortion function evolution at the bouncing point for each model are discussed.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Santosh V. Lohakare, B. Mishra, S. K. Maurya, Ksh. Newton Singh
Summary: In this study, the parametrization approach was used to recreate cosmological models, allowing for the incorporation of observational data. The results showed a transition from a decelerating to an accelerating stage of cosmic evolution, driven by quintessence dark energy. The violation of the strong energy conditions and the age of the Universe were also investigated.
PHYSICS OF THE DARK UNIVERSE
(2023)
Article
Physics, Particles & Fields
S. N. Sajadi
Summary: In this paper, we extend the AdS/QCD model to quadratic gravity to study the influence of gravity. We find an anisotropic black brane solution in a 5D Einstein-Gauss-Bonnet-two Maxwell-dilaton system. The system is characterized by an arbitrary exponent, a dilaton field, a time component of the first Maxwell field, and a magnetic component of the second Maxwell field. We investigate three cases and consider the effects of the theory parameter and the anisotropic parameter. The blackening function exhibits a thermodynamic phase transition between small/large and AdS/large black brane with suitable chemical potential and other parameters.
EUROPEAN PHYSICAL JOURNAL C
(2023)
Article
Physics, Particles & Fields
Li-Ming Cao, Liang-Bi Wu
Summary: This article discusses that in the four-dimensional Einstein-Gauss-Bonnet gravity, to ensure the existence of a well defined linearized gravitational wave equation, the spacetime must be locally conformally flat.
EUROPEAN PHYSICAL JOURNAL C
(2022)
Article
Physics, Multidisciplinary
M. Z. Bhatti, Z. Yousaf, T. Ashraf
Summary: This paper discusses the viable and analytic solution of the spherically symmetric gravastar model under the influence of modification of Gauss-Bonnet gravity, f(G) gravity. The mathematical formalism of the gravastar's three regions and the analysis of different physical features are presented, resulting in an exact and singularity-free model within an alternative theory framework.
CHINESE JOURNAL OF PHYSICS
(2021)
Article
Astronomy & Astrophysics
Sandipan Sengupta
Summary: In this study, we establish an Einstein-Gauss-Bonnet theory in four dimensions based on extra dimensions with vanishing metrical length. The effective field equations of the theory depend solely on the four-metric and exhibit a quadratic curvature nonlinearity without higher than second-order derivatives. Unlike previous proposals, our formalism does not require classical regularization of divergences and is not equivalent to Horndeski gravity. The theory is generally covariant and independent of compactification. The vacuum field equations allow for FLRW cosmologies with nonsingular bounce and self-accelerating Universe, as well as spherically symmetric black holes more general than Schwarzschild. Furthermore, the quadratic theory of gravity remains valid against the inclusion of higher Lovelock densities in 5 + 2n dimensions.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Physics, Multidisciplinary
Sanjay Mandal, N. Myrzakulov, P. K. Sahoo, R. Myrzakulov
Summary: Symmetric teleparallel gravity is a theory consistent with the vanishing affine connection and serves as an alternative and simpler geometric formulation of general relativity. Researchers have explored cosmological bouncing scenarios in a flat Friedmann-Limaitre-Robertson-Walker spacetime using two different Lagrangian forms of f(Q). Analysis of energy conditions and stability has been successfully conducted for both models to demonstrate a matter bounce.
EUROPEAN PHYSICAL JOURNAL PLUS
(2021)
Article
Physics, Particles & Fields
E. Elizalde, G. G. L. Nashed, S. Nojiri, S. D. Odintsov
EUROPEAN PHYSICAL JOURNAL C
(2020)
Article
Physics, Mathematical
V Dzhunushaliev, V Folomeev, G. Nurtayeva, S. D. Odintsov
INTERNATIONAL JOURNAL OF GEOMETRIC METHODS IN MODERN PHYSICS
(2020)
Article
Astronomy & Astrophysics
S. D. Odintsov, V. K. Oikonomou, F. P. Fronimos
PHYSICS OF THE DARK UNIVERSE
(2020)
Article
Astronomy & Astrophysics
Shin'ichi Nojiri, Sergei D. Odintsov, V. K. Oikonomou
PHYSICS OF THE DARK UNIVERSE
(2020)
Article
Astronomy & Astrophysics
A. Astashenok, S. Capozziello, S. D. Odintsov, V. K. Oikonomou
Article
Physics, Multidisciplinary
A. N. Makarenko, A. V. Timoshkin
Summary: The holographic principle is applied to describe the early stage of the Universe's evolution, using viscous liquid and holographic cutoff concepts. Calculations of the infrared radius and derivation of energy conservation laws are conducted within this framework, presenting the viscous liquid as a generalization of holographic energy.
RUSSIAN PHYSICS JOURNAL
(2021)
Article
Astronomy & Astrophysics
Shin'ichi Nojiri, Sergei D. Odintsov
PHYSICS OF THE DARK UNIVERSE
(2020)
Article
Astronomy & Astrophysics
S. D. Odintsov, V. K. Oikonomou, F. P. Fronimos, S. A. Venikoudis
PHYSICS OF THE DARK UNIVERSE
(2020)
Biographical-Item
Multidisciplinary Sciences
Sergei D. Odintsov
Article
Physics, Multidisciplinary
A. N. Makarenko, A. Timoshkin
Summary: This paper investigates cosmological models with inhomogeneous viscous fluids and a logarithmic equation of state in the Friedman-Lemaitre-Robertson-Walker Universe, and examines the influence of thermal effects on the singularity types of the dark Universe caused by Hawking radiation. The results show that, taking into account the viscosity property of dark fluid, thermal radiation can qualitatively change the type of the Big Rip singularity, potentially leading to the absence of singularities in the Universe.
RUSSIAN PHYSICS JOURNAL
(2022)
Review
Multidisciplinary Sciences
Sergei D. Odintsov, Vasilis K. Oikonomou, Ratbay Myrzakulov
Summary: In this work, the authors exhaustively study the effects of modified gravity on the energy spectrum of the primordial gravitational waves background. They provide calculations for various cases of modified gravity, focusing on specific forms of interest. They also present the exact form of a parameter involved in the calculation of the effects of modified gravity on the energy spectrum for the first time.
Article
Astronomy & Astrophysics
Sergei D. Odintsov, Tanmoy Paul
Summary: This work explores the influence of a Type-IV singularity on the dynamics of a bouncing universe in the context of a ghost-free Gauss-Bonnet theory of gravity. It is found that when the singularity has a global effect on spacetime, the scalar power spectrum becomes red-tilted and the tensor-to-scalar ratio is incompatible with observational data. However, if the singularity only locally affects spacetime around the time of occurrence, the observable quantities are compatible with Planck data.
Editorial Material
Multidisciplinary Sciences
Sergei D. D. Odintsov
Editorial Material
Multidisciplinary Sciences
Sergei D. Odintsov
Article
Multidisciplinary Sciences
Artyom V. Astashenok, Sergey D. Odintsov, Vasilis K. Oikonomou
Summary: This study investigates the Chandrasekhar mass limit of white dwarfs in various models of f (R) gravity. Two equations of state for stellar matter are used: the simple relativistic polytropic equation and the realistic Chandrasekhar equation of state. The solution for any model of f (R) = R + beta R-m gravity shows that the stellar mass decreases compared to standard General Relativity. For realistic equations of state, there is a value of the central density for which the mass of a white dwarf peaks. This implies that in modified gravity, there exists a minimum radius for stable white dwarfs, which is greater than in General Relativity. The behavior of the Chandrasekhar mass limit in f (R) gravity is also investigated.
Article
Astronomy & Astrophysics
Nelson R. F. Braga, Octavio C. Junqueira
Summary: This study investigates the influence of rotation on the transition temperature of strongly interacting matter produced in non-central heavy ion collisions. By using a holographic description of an AdS black hole, the authors extend the analysis to the more realistic case where the matter spreads over a region around the rotational axis. The results show the coexistence of confined and deconfined phases and are consistent with the concept of local temperature in rotating frames developed by Tolman and Ehrenfest.
Article
Astronomy & Astrophysics
Bing Sun, Jiachen An, Zhoujian Cao
Summary: This paper investigates the effect of gravitational constant variation on the propagation of gravitational waves. By employing two analytical methods, the study finds that variations in the gravitational constant result in amplitude and phase corrections for gravitational waves, and the time variation of the gravitational constant can be constrained through the propagation of gravitational waves.
Article
Astronomy & Astrophysics
Abdellah Touati, Zaim Slimane
Summary: This letter presents the first study of Hawking radiation as a tunneling process within the framework of non-commutative gauge theory of gravity. The non-commutative Schwarzschild black hole is reconstructed using the Seiberg-Witten map and the star product. The emission spectrum of outgoing massless particles is computed using the quantum tunneling mechanism. The results reveal pure thermal radiation in the low-frequency scenario, but a deviation from pure thermal radiation in the high-frequency scenario due to energy conservation. It is also found that noncommutativity enhances the correlations between successively emitted particles.
Article
Astronomy & Astrophysics
Shahar Hod
Summary: The travel times of light signals between two antipodal points on a compact star's surface are calculated for two different trajectories. It is shown that, for highly dense stars, the longer trajectory along the surface may have a shorter travel time as measured by asymptotic observers. A critical value of the dimensionless density-area parameter is determined for constant density stars to distinguish cases where crossing through the star's center or following a semi-circular trajectory on the surface has a shorter travel time as measured by asymptotic observers.
