Article
Astronomy & Astrophysics
Meysam Motaharfar, Parampreet Singh
Summary: In Vilenkin's tunneling wave function proposal, the expanding Universe is born through a barrier from nothing at the zero scale factor. The viability of this proposal is explored for the spatially-closed Friedmann-Lemaitre-Robertson-Walker model with a positive cosmological constant and quantum gravity modifications. The effective spacetime description of loop quantum cosmology (LQC) is used, which replaces the big bang singularity with a bounce due to holonomy modifications.
Article
Astronomy & Astrophysics
Luis M. Sanchez, Hernando Quevedo
Summary: In this study, we investigate the relationship between gravity and thermodynamics in dynamic systems by considering the apparent horizon of the FLRW spacetime as a thermodynamic system. We derive the fundamental equation in the entropy representation and explore the consequences of satisfying classical laws of thermodynamics. Our investigation focuses on FLRW spacetimes with and without a cosmological constant. We find that the interpretation of the apparent horizon as an isolated thermodynamic system is only possible under certain conditions, as the analogy does not hold for all parameter values and the entire evolution of the horizon. However, we demonstrate that the generalized second law of thermodynamics remains valid.
Article
Physics, Multidisciplinary
Abdul Jawad, G. Abbas, Iqra Siddique, G. Mustafa
Summary: The thermodynamics of a new type of regular black hole associated with the cosmological constant in nonlinear electrodynamics has been explored. The study investigates various thermodynamic quantities such as Hawking temperature, the first law of thermodynamics, equation of state, and Gibbs free energy using the modified entropy with Gauss-Bonnet coupling. Additionally, the study explores the interesting aspect of Hawking-Page phase transitions for this black hole and examines the phase transitions using the temperature-Gibbs free energy plot.
EUROPEAN PHYSICAL JOURNAL PLUS
(2022)
Article
Physics, Particles & Fields
K. K. Nandi, R. N. Izmailov, R. Kh. Karimov, A. A. Potapov
Summary: In this paper, a class of LV corrected Schwarzschild black holes are studied, and their horizon patterns are numerically explored. The energy conditions are relaxed and it is found that three types of black holes satisfy Thorne's hoop conjecture, while the remaining type does not. Additionally, the existence of braneworld tidal charge black holes shows a qualitative difference in the LV correction to planetary perihelion advance compared to ordinary black holes.
EUROPEAN PHYSICAL JOURNAL C
(2023)
Article
Physics, Particles & Fields
Ge-Rui Chen
Summary: In this note, the modified Friedmann equation of a Friedmann-Robertson-Walker (FRW) Universe with any spatial curvature is derived using the concept of the emergence of cosmic space suggested by Padmanabhan and Tsallis and Cirto entropy in (n + 1) dimension. The paper further investigates the consistency between the law of emergence and the maximization of horizon entropy in the context of Tsallis and Cirto entropy. The results highlight the deep connection between the law of emergence and horizon thermodynamics.
EUROPEAN PHYSICAL JOURNAL C
(2022)
Article
Physics, Multidisciplinary
Z. Yousaf, M. Z. Bhatti, Maxim Khlopov, H. Asad
Summary: This paper examines the characteristics of static irrotational matter with hyperbolic symmetry using metric f(R) gravity. It reveals the existence of an empty core and negative effective energy density, which could be crucial for understanding quantum field events. Relationships among matter variables and structure scalars are determined, and hyperbolically symmetric cosmological models are studied through generating functions.
Article
Physics, Multidisciplinary
Muhammad Naeem, Aysha Bibi
Summary: In this study, new entropic force models were proposed by using dimensionless parameters to quantify non-extensivity and quantum-gravitational deformation, and by introducing the Hubble horizon. The cosmological consequences of these models and the late time accelerating expansion of the universe were investigated. It was found that the expansion of the universe is uniform when using non-additive Tsallis entropy and Barrow entropy, similar to the cases of Bekenstein entropy and dark energy.
EUROPEAN PHYSICAL JOURNAL PLUS
(2023)
Article
Multidisciplinary Sciences
Z. Yousaf, M. Z. Bhatti, U. Farwa
Summary: This article investigates the physical features of static axial sources that produce complexity within the matter configuration within the perspective of f (R, T) theory. The contracted Bianchi identities of effective and normal matter are used to develop the conservation equations. By splitting the curvature tensor to compute structure scalars, the physical aspects of the source are determined. The complexity of the system is calculated by exploring the evolving source and the corresponding propagation equations.
Article
Physics, Particles & Fields
Xiangdong Zhang
Summary: This paper extends the thermodynamic properties of loop quantum cosmology (LQC) to a new model with the Lorentz term, showing that the effective density and effective pressure in the modified Friedmann equation not only determine the evolution of the universe but also serve as thermodynamic quantities. The first law of thermodynamics of LQC remains valid with the help of the Misner-Sharp energy, providing precise physical meaning to the effective matter density and effective pressure.
EUROPEAN PHYSICAL JOURNAL C
(2021)
Article
Physics, Particles & Fields
Meng-Yao Zhang, Hao Chen, Hassan Hassanabadi, Zheng-Wen Long, Hui Yang
Summary: The classification of critical points of charged topological black holes in anti-de Sitter spacetime under the Power Maxwell Invariant (PMI)-massive gravity is studied in the framework of black hole chemistry. It is found that 4-dimensional black holes have only one topological class, while 5-dimensional and higher dimensional black holes belong to two different topology classes. The traditional critical point corresponds to the maximum extreme point of temperature with negative topological charge, while the novel critical point corresponds to the minimum extreme point of temperature with opposite topological charge.
EUROPEAN PHYSICAL JOURNAL C
(2023)
Article
Astronomy & Astrophysics
Hamna Asad, Zeeshan Yousaf
Summary: The core objective of this manuscript is to conduct a comprehensive investigation into the characteristics of static matter configurations with hyperbolic symmetry, which may potentially serve as the formation of corresponding spacetime within f(R,T,Q) gravity. We find that such matter distributions exhibit anisotropic pressure, with only two unequal primary stresses and a negative energy density. Negative matter densities are commonly suggested in extreme cosmological and astrophysical scenarios, especially with regards to quantum phenomena occurring within the horizon. Ultimately, we establish a generic formalism that allows the expression of any static hyperbolically symmetric (HS) fluid solution in terms of two generating functions (GFs).
Article
Astronomy & Astrophysics
Tomohiro Harada, Takahisa Igata, Takuma Sato, Bernard Carr
Summary: In this paper, we classify the Friedmann-Lemaitre-Robertson-Walker solutions with spatial curvature K = 0, +/- 1 for perfect fluids with linear equation of state p = w rho without assuming any energy conditions. We extend our previous work to include all geodesics and parallelly propagated (p.p.) curvature singularities. Our study reveals that there are no non-null geodesics emanating from or terminating at the null portion of conformal infinity, and that the initial singularity for certain parameter ranges is a null non-scalar polynomial curvature singularity.
CLASSICAL AND QUANTUM GRAVITY
(2022)
Article
Astronomy & Astrophysics
Thanasis Karakasis, Nick E. Mavromatos, Eleftherios Papantonopoulos
Summary: We study exact solutions for regular compact objects in higher-dimensional general relativity theories with a phantom scalar field. We find that the solutions, which do not have a central singularity, depend on both the scalar-hair charge and black-hole mass. We demonstrate the consistency of these solutions and discuss their thermodynamics properties.
Article
Astronomy & Astrophysics
Daniele Gregoris, Yen Chin Ong
Summary: This study proposes a new entropy density function based on the Weyl curvature, using combinations of other curvature invariants. The method works for static black hole solutions and can be extended to higher dimensions. The findings may provide insight into the physical interpretation of black hole entropy.
Article
Astronomy & Astrophysics
D. J. Zamora, C. Tsallis
Summary: We analyze the thermodynamical consistency of entropic-force cosmological models using a generalized entropy scaling. By determining the temperature of the universe horizon and comparing with supernovae data, we evaluate the performance of these models. Our analysis provides insights into the form of cosmological entropy and temperature and identifies thermodynamically consistent models.
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.