Article
Physics, Particles & Fields
Joao Luis Rosa, D. Bazeia, A. S. Lobao Jr
Summary: In this work, we study braneworld configurations in the scalar-tensor representation of the f (R, T) gravity theory in the presence of a Cuscuton term in the source field matter Lagrangian. We derive the scalar-tensor representation and obtain its equations of motion. We then investigate two different models for the source field in a flat braneworld model with one extra dimension for the general case of a f (R, T) theory. The solutions are obtained numerically due to the complexity of the field equations. The Cuscuton term effectively enhances the effect, increasing the height of the stability potential barrier and the depth of the minimum of the graviton zero-mode on the brane. Additionally, we examine the cases of F(R) + T and R + G (T), and demonstrate the essential role of the scalar field phi in the development of internal structure on the brane.
EUROPEAN PHYSICAL JOURNAL C
(2022)
Article
Astronomy & Astrophysics
Rui-Hui Lin, Xiang-Hua Zhai
Summary: General relativity can be formulated equivalently with a non-Riemannian geometry involving a nonmetricity Q but vanishing curvature R and torsion T. Modification based on this description leads to f(Q) gravity. The application of f(Q) gravity to spherically symmetric configurations is explored, demonstrating effects on external and internal solutions of compact stars through different modifications.
Article
Astronomy & Astrophysics
Joao Luis Rosa
Summary: This study investigates the junction conditions for matching between two spacetimes at a separation hypersurface in the perfect-fluid version of f(R, T) gravity, considering both geometrical and scalar-tensor representations. General junction conditions are derived for a thin shell separating the spacetimes, with a focus on smooth matching when the stress-energy tensor of the thin shell vanishes. The set of junction conditions includes constraints on the continuity of the trace of the stress-energy tensor and its partial derivatives, leading to implications for spherical symmetric thin shells and specific forms of the function f(R, T).
Article
Astronomy & Astrophysics
Mauricio Bellini, Luis Santiago Ridao
Summary: This paper investigates a preinflationary model where the background dynamics is driven by curvaton fluctuations. Two possible solutions with the same equation of state are explored, and conditions for a preinflationary scenario are obtained. The dynamics of gravitational waves and the ln(k)-spectrum of the scalar curvature on the extended manifold are also studied.
PHYSICS OF THE DARK UNIVERSE
(2022)
Article
Physics, Particles & Fields
Joao Luis Rosa, A. S. Lobao Jr, D. Bazeia
Summary: In this work, we studied braneworld models in generalized f(R, T) gravity theories and used the scalar-tensor representation theory. By introducing auxiliary fields and relating them to the source field, we analyzed four possibilities regarding compactification and asymmetry of the brane. We found that in certain models, the solutions of the auxiliary fields are significantly influenced by the source field, exhibiting different behaviors.
EUROPEAN PHYSICAL JOURNAL C
(2022)
Article
Physics, Multidisciplinary
J. A. Astorga-Moreno, E. A. Mena-Barboza
Summary: Modified gravity theories have gained significant attention in the past decade. This study utilizes deformed phase space in f(R) gravity to derive the Wheeler-DeWitt equation in the Quantum Cosmology scenario for a Friedmann-Lemaitre-Robertson-Walker model. Furthermore, a function f(R) that corresponds to the -Cold Dark Matter model is also considered.
Article
Physics, Multidisciplinary
Jay Solanki
Summary: This article develops a physically realistic model of compact stars undergoing gravitational collapse in f(R) gravity and finds analytical solutions describing the interior space-time metric, energy density, pressures, and heat flux density. The study also explores the physical properties of collapsing stars, providing insights into their inherent nature during gravitational collapse.
EUROPEAN PHYSICAL JOURNAL PLUS
(2022)
Article
Astronomy & Astrophysics
Joao C. Lobato, Isabela S. Matos, Mauricio O. Calvao, Ioav Waga
Summary: The study introduces an alternative choice of variables for treating f(R) models in their Palatini formulation, leading to the derivation of general results and a complete description of the phase space for exponential gravity. It is shown that Palatini exponential gravity theories have a final attractor critical point with specific effective equation of state parameters. Comparison of analytical results with numerical solutions of the field equations is also conducted.
Article
Astronomy & Astrophysics
Z. Yousaf, Maxim Yu Khlopov, Bander Almutairi, Ume Farwa
Summary: In this study, we analyze gravitationally decoupled sources in the context of f (R) gravity using the CGD strategy. By finding the exact solutions of anisotropic spherical complex systems and deducing deformed functions, we investigate the energy transition and stability influenced by the decoupling parameter.
PHYSICS OF THE DARK UNIVERSE
(2023)
Article
Astronomy & Astrophysics
P. J. Pompeia
Summary: The analysis of f(T, del(mu 1) T, . . . ,del(mu n) . . . del(mu 1) T) gravity in the Jordan and Einstein frames was presented. The equivalence with a scalar-multitensor theory was proved for systems with a regular Hessian matrix in both frames. Introducing an auxiliary tensor of the same order for each derivative reduced the differential equation for the tetrad field to second order, but led to a system of coupled equations for the auxiliary fields.
Article
Astronomy & Astrophysics
Metin Gurses, Yaghoub Heydarzade, Cetin Senturk
Summary: In this study, we investigate the Kerr-Schild-Kundt class of metrics in generic gravity theories with Maxwell's field and prove that these metrics linearize and simplify the field equations of such theories.
Article
Physics, Particles & Fields
Oleksii Sokoliuk, Alexander Baransky
Summary: We study Morris-Thorne static traversable wormhole solutions in different modified theories of gravity and derive suitable shape functions by numerically solving the Einstein field equations. The stability of Morris-Thorne wormholes and energy conditions are analyzed, and general formulas for the extra force in MTOV due to the non-conserved stress-energy tensor are derived.
EUROPEAN PHYSICAL JOURNAL C
(2021)
Article
Physics, Multidisciplinary
Jun Wang, Ling-Xuan Qiang, Tian-Qiang Zhang, Zhi-Song Wang, Lu-Yu Li
Summary: This paper explores the thermodynamics of the Friedmann-Lemaitre-Robertson-Walker universe in f(R) theories of gravity with arbitrary matter-geometry coupling, confirming the equivalence between modified Friedmann equations and the first law of thermodynamics. Laws of thermodynamics are obtained and validated through observational results.
COMMUNICATIONS IN THEORETICAL PHYSICS
(2022)
Article
Astronomy & Astrophysics
Jonathan J. Heckman, Andrew P. Turner, Xingyang Yu
Summary: This study presents a detailed realization of the quantum field theory ensembles in D < 4 spacetime dimensions, allowing for a random averaging of coupling constants. The resulting volume, when each member of the ensemble is a conformal field theory with a standard semiclassical holographic dual, can be interpreted as an asymptotically anti-de Sitter space geometry with a distribution of boundary components joined by wormhole configurations. This construction provides a UV completion of the proposal for a high-dimensional Hilbert space for baby universes, while remaining consistent with the proposed swampland constraints.
Article
Physics, Particles & Fields
Mutasem Z. Bani-Fwaz, M. Z. Bhatti, Z. Yousaf, U. Farwa, Ahmed M. Galal
Summary: This paper investigates the continuation of LTB space-time for dissipative dust configuration in the direction of Palatini f(R) theory. The effects of kinematical variables and curvature invariant on the proposed fluid configuration are explored. The significance of computing Palatini f(R) scalar variables for dissipative dust spheres through the orthogonal splitting of Riemann-tensor is reported. Two subcases of LTB space-time are carried out to note down its symmetric aspects.
EUROPEAN PHYSICAL JOURNAL C
(2022)
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.