Article
Physics, Particles & Fields
Dmitry Chirkov, Alex Giacomini, Sergey A. Pavluchenko, Alexey Toporensky
Summary: The paper systematically investigates solutions with static compact extra dimensions and expanding three-dimensional subspace, providing a scheme for constructing solutions with stability analysis. It finds that solutions with negative spatial curvature of extra dimensions are always stable, while those with positive curvature are stable for a narrow range of parameters. Differences between positive and negative curvature cases, including the coexistence with maximally-symmetric solutions, are noted and discussed.
EUROPEAN PHYSICAL JOURNAL C
(2021)
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
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
Physics, Multidisciplinary
Amritendu Haldar, Anendu Haldar
Summary: In this article, the thermodynamic properties of a black hole solution in Gauss-Bonnet gravity are analyzed by studying the variations of Gibbs free energy and Helmholtz free energy. The phase transition and critical behavior of the black holes are examined and a relation similar to the van der Waals system is found. The thermal stability is also investigated by computing the specific heat with higher-order correction.
INTERNATIONAL JOURNAL OF THEORETICAL PHYSICS
(2023)
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
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
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
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
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, Particles & Fields
Yi-Li Wang, Xian-Hui Ge
Summary: This paper investigates the Einstein-Maxwell-Gauss-Bonnet-axion theory in 4-dimensional spacetime through a Kaluza-Klein-like process. By obtaining the dyonic black hole solution coupled with higher derivative terms, the behavior of shear viscosity to entropy density ratio at different temperatures is studied. It is found that the ratio of uncharged black holes violates a specific bound at low temperatures, and the main feature of this ratio remains almost unchanged in 4 dimensions.
EUROPEAN PHYSICAL JOURNAL C
(2021)
Article
Astronomy & Astrophysics
V. K. Oikonomou
Summary: In this work, a refined Einstein-Gauss-Bonnet inflationary theoretical framework is provided, which is compatible with observational constraints on the gravitational wave speed. By introducing new assumptions and conditions, much simpler expressions for the slow-roll indices, tensor and scalar spectral indices, and tensor-to-scalar ratio are successfully derived. A particular model with a blue-tilted tensor spectral index is exemplified, showing compatibility with the latest Planck data and potential to describe the NANOGrav result according to recent literature.
CLASSICAL AND QUANTUM GRAVITY
(2021)
Article
Astronomy & Astrophysics
Kalin Staykov, Daniela D. Doneva
Summary: A new nonlinear mechanism for black hole scalarization, different from the standard spontaneous scalarization, is studied in multiscalar Gauss-Bonnet gravity. Numerical calculations demonstrate the existence of scalarized black holes for different coupling functions and scalar field target spaces.
Article
Physics, Particles & Fields
Kalin Staykov, Radostina Z. Zheleva
Summary: In this paper, we construct novel non-topological, spontaneously scalarized neutron stars in multi-scalar Gauss-Bonnet gravity with maximally symmetric target space. The theory allows solutions with trivial scalar field for certain classes of coupling functions, which coincide with the general relativistic ones. However, within a certain range of parameters, these solutions lose stability and new branches of solutions with nontrivial scalar field bifurcate from the trivial branch.
EUROPEAN PHYSICAL JOURNAL C
(2022)
Article
Astronomy & Astrophysics
Dmitry Chirkov, Alex Giacomini, Alexey Toporensky
GENERAL RELATIVITY AND GRAVITATION
(2020)
Article
Physics, Particles & Fields
Dmitry Chirkov, Alex Giacomini, Sergey A. Pavluchenko, Alexey Toporensky
Summary: The paper systematically investigates solutions with static compact extra dimensions and expanding three-dimensional subspace, providing a scheme for constructing solutions with stability analysis. It finds that solutions with negative spatial curvature of extra dimensions are always stable, while those with positive curvature are stable for a narrow range of parameters. Differences between positive and negative curvature cases, including the coexistence with maximally-symmetric solutions, are noted and discussed.
EUROPEAN PHYSICAL JOURNAL C
(2021)
Article
Physics, Particles & Fields
E. D. Emtsova, M. Krssak, A. N. Petrov, A. V. Toporensky
Summary: This study examines various methods of constructing conserved quantities in the Teleparallel Equivalent of General Relativity (TEGR), with a focus on Noether charges in the covariant formulation. The physical implications of choosing the observer's four-velocity or a Killing vector as 4 in different frames, based on the example of the Schwarzschild solution, are discussed. Additionally, an analysis of determining inertial spin connections for different tetrads used in calculations is presented, revealing some ambiguity in the method of switching-off gravity.
EUROPEAN PHYSICAL JOURNAL C
(2021)
Article
Astronomy & Astrophysics
Daniel Muller, Alexey Toporensky
Summary: In quadratic gravity, a static cosmological solution can exist and be stable for a universe filled with only one type of perfect fluid, with different conditions and stability depending on the curvature of the universe.
GENERAL RELATIVITY AND GRAVITATION
(2021)
Article
Multidisciplinary Sciences
Alexey V. Toporensky, Oleg B. Zaslavskii
Summary: This study considers the spacetime of a spherically symmetric black hole with a simple horizon. Due to the failure of a standard coordinate frame near the horizon, continuation and construction of regular frames are required. It is shown that Kruskal-Szekeres and Lemaitre frames stem from the same root, providing a more general scheme.
Article
Physics, Particles & Fields
Laur Jarv, Alexey Toporensky
Summary: This study reconsiders the dynamical systems approach to analyze inflationary universe in the Jordan frame models of scalar field nonminimally coupled to curvature. It finds that the adopted set of variables allows clear distinction between different asymptotic states including the kinetic and inflationary regimes. The study also provides a comprehensive picture of possible initial conditions leading to sufficient inflationary expansion and shows how they approximate the leading inflationary attractor solution. Additionally, it examines the impact of nonminimal coupling on the range of good initial conditions using quadratic and quartic potential models as examples.
EUROPEAN PHYSICAL JOURNAL C
(2022)
Article
Physics, Particles & Fields
A. Radosz, A. V. Toporensky, O. B. Zaslavskii
Summary: The problem of speed inside the Schwarzschild black hole is investigated, and it is found that the relative speed of objects approaching the singularity tends to the speed of light. An exception is observed when both objects move in the same plane with parallel angular momenta. This result reflects the anisotropic nature of the black hole's dynamics and implies collisions near the singularity result in infinite energy.
EUROPEAN PHYSICAL JOURNAL C
(2023)
Article
Physics, Particles & Fields
E. D. Emtsova, A. N. Petrov, A. V. Toporensky
Summary: We derive conservation laws in Symmetric Teleparallel Equivalent of General Relativity (STEGR) by directly applying Noether's theorem. This approach allows us to construct covariant conserved currents, corresponding superpotentials, and invariant charges. We introduce the concept of turning off gravity to define the flat and torsionless connection in STEGR, which is a necessary component in our constructions. We calculate the energy density and total mass in simple solutions to test our results and discuss possible solutions for the ambiguities in obtaining the connection that affect the values of conserved quantities.
EUROPEAN PHYSICAL JOURNAL C
(2023)
Article
Physics, Particles & Fields
A. V. Toporensky, O. B. Zaslavskii
Summary: We study general radially moving frames in the background of nonextremal black holes similar to the Schwarzschild metric. We generalize the Lemaitre approach and construct free-falling frames composed of reference particles with arbitrary specific energy, including negative energy. We provide the general formula for the 3-velocity of a freely falling particle with respect to a frame with a specific energy. We investigate the relation between the properties of these frames near a horizon and the Banados-Silk-West effect of indefinite growth of energy of particle collisions. Using our radially moving frames, we also consider the nonradial motion of test particles, including regions near the horizon and singularity. We discuss the properties of the Lemaitre time at horizons depending on the frame and sign of particle energy.
EUROPEAN PHYSICAL JOURNAL C
(2023)
Article
Astronomy & Astrophysics
A. V. Toporensky, O. B. Zaslavskii
Summary: This methodological paper extends previous results obtained for pure radial motion to consider the geodesic motion of particles in spherically symmetric black hole space-times, including nonradial motion and the possibility of an observer having nonzero angular momentum. The approach provides a simple physical interpretation of redshifts (blueshifts) inside the horizon, including the region near the singularity, and is consistent with recent results obtained by direct calculations.
GRAVITATION & COSMOLOGY
(2021)
Article
Physics, Particles & Fields
Maria A. Skugoreva, Alexey Toporensky
EUROPEAN PHYSICAL JOURNAL C
(2020)
Article
Astronomy & Astrophysics
Swagat S. Mishra, Daniel Muller, Aleksey Toporensky
Article
Astronomy & Astrophysics
Ekaterina O. Pozdeeva, Mayukh Raj Gangopadhyay, Mohammad Sami, Alexey Toporensky, Sergey Yu Vernov
Article
Astronomy & Astrophysics
Alexey Toporensky, Petr Tretyakov
Article
Astronomy & Astrophysics
Mikhail M. Ivanov, Marko Simonovic, Matias Zaldarriaga
