Article
Physics, Mathematical
Nisha Godani, Gauranga C. Samanta
Summary: In this paper, Morris Thorne wormholes in the context of f(R) gravity are investigated. The shape function is defined, and the equation of state and f(R) function are derived. The wormhole solutions are obtained and energy conditions are examined. The f(R) model is found to be consistent with local gravity tests and stability of cosmological perturbations and late-time de Sitter point. Furthermore, the cosmological evolution is explored using the Friedman-Robertson-Walker (FRW) metric in f(R) gravity.
INTERNATIONAL JOURNAL OF GEOMETRIC METHODS IN MODERN PHYSICS
(2022)
Article
Astronomy & Astrophysics
Projjwal Banerjee, Meng-Ru Wu, S. K. Jeena
Summary: GW170817 confirms binary neutron star mergers as one of the sites for rapid neutron capture (r-process). However, there are uncertainties in the nucleosynthesis calculations and additional sites may be needed to explain all observations. This study examines the abundance and evolution of short-lived radioactive isotopes (SLRIs) in the early Solar system and finds that I-129 and Cm-247 in the ESS do not solely come from a single major event, but have contributions from minor sources as well.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Physics, Multidisciplinary
Roger Hurtado, Robel Arenas
Summary: A cosmologically viable hypergeometric model has been derived based on the requirements of asymptotic behavior towards Lambda CDM, the presence of an inflection point in the f (R) curve, and the viability conditions dictated by the phase space curves (m, r). The models were expressed in terms of a dimensionless variable and differential equations were formulated to establish the relationship between certain functions. The resulting solutions yielded specific types of models, but it was subsequently discovered that these differential equations correspond to a more general hypergeometric model.
Article
Physics, Multidisciplinary
M. Sharif, M. Zeeshan Gul
Summary: This paper investigates static wormhole solutions through Noether symmetry approach in the context of energy-momentum squared gravity, and finds that realistic traversable and stable wormhole solutions are obtained for a particular model of this gravity.
EUROPEAN PHYSICAL JOURNAL PLUS
(2021)
Article
Astronomy & Astrophysics
Suresh Kumar, Rafael C. Nunes, Supriya Pan, Priya Yadav
Summary: In this study, the f(R) gravity framework is constrained using the latest observational data, and it is found to be consistent with general relativity at a 95% confidence level.
PHYSICS OF THE DARK UNIVERSE
(2023)
Article
Physics, Multidisciplinary
R. Saleem, Aqsa Saleem
Summary: The aim of this article is to investigate baryogenesis in the isotropic universe model under f (R, T, Q, T) gravity, with R, T, Q, and T representing the Ricci scalar, the energy-momentum tensor (EMT) trace, non-metricity scalar, and torsion scalar, respectively. Two fluid types, w = 0 and w = 1, are used to study baryogenesis and its generalized form, using power-law and de-sitter type solutions for the scale factor. The study compares different gravity models and concludes that the linear model is more efficient in providing physically acceptable results for baryogenesis.
CHINESE JOURNAL OF PHYSICS
(2023)
Article
Multidisciplinary Sciences
Rishi Kumar Tiwari, Bhupendra Kumar Shukla, Deger Sofuoglu, Dilay Kosem
Summary: In this study, a specific form of the time-dependent deceleration parameter is used to examine the accelerated expansion and phase transition in the flat FRW model of the universe within the context of f(R,T) gravity theory. The modified field equations are solved for a choice of f(R,T) = R+2f(T). The best fit values for the model parameters are determined using recent observational datasets, including 57 points from Cosmic Chronometers (CC) datasets and 1048 points from Pantheon supernovae datasets. Bayesian analysis and likelihood function, together with Markov Chain Monte Carlo (MCMC) method, are applied at 1s and 2s confidence levels. The physical behavior of parameters, such as density, pressure, and cosmographic parameters, corresponding to the constrained values of the model parameters, is then analyzed. Looking at the deceleration parameter, it is observed that the universe has transitioned from a decelerating expansion phase to an accelerating phase. Therefore, the cosmological model f(R,T) discussed in this study can successfully explain the accelerating expansion of the late universe without resorting to any dark energy component in the energy-momentum tensor.
Article
Physics, Particles & Fields
Fernanda Alvarim Silveira, Rodrigo Maier, Santiago Esteban Perez Bergliaffa
Summary: This study presents a model that generalizes Schwarzschild's homogeneous star by adding a transition zone for the density near the surface, and numerically integrates the modified TOV equations for the f(R)=R+lambda R2 Palatini theory to obtain finite configurations. Depending on the values of the relevant parameters, objects more compact, less compact, or equally compact as those obtained in GR with the same density profile have been shown to exist. Particularly, in some region of the parameter space, the compactness is close to that set by the Buchdahl limit.
EUROPEAN PHYSICAL JOURNAL C
(2021)
Article
Physics, Mathematical
Bhupendra Kumar Shukla, R. K. Tiwari, D. Sofuoglu
Summary: In this article, the dynamical behavior of the universe is examined in the context of the f(R, G) theory of gravity, which incorporates the Ricci scalar and Gauss-Bonnet invariant. The best fit values of model parameters are predicted to be in agreement with recent observational datasets, using the CC, Pantheon and BAO datasets, Bayesian analysis, likelihood function, and MCMC method. The obtained f(R, G) model exhibits a transition from decelerating to accelerating expansion of the universe, explaining the late accelerating expansion without the need for dark energy.
INTERNATIONAL JOURNAL OF GEOMETRIC METHODS IN MODERN PHYSICS
(2023)
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, Mathematical
Lakhan Jaybhaye, Sanjay Mandal, P. K. Sahoo
Summary: In this paper, we extend the Hilbert-Einstein action to analyze several interesting features of the theory, deriving motion equations and energy conditions. By using cosmographic parameters, we constrain the model parameters and observe the current accelerated expansion of the universe.
INTERNATIONAL JOURNAL OF GEOMETRIC METHODS IN MODERN PHYSICS
(2022)
Article
Astronomy & Astrophysics
Yves Marrocchi, Maxime Piralla, Francois L. H. Tissot
Summary: The recent discovery of nontraditional isotopic systems has shown that meteorites can be divided into two groups, noncarbonaceous and carbonaceous, which represent material from different parts of the solar system. A new theory suggests that there are three distinct reservoirs in the solar system. This study supports the existence of only two reservoirs and the presence of a specific type of carbonaceous chondrite with a distinct source region.
ASTROPHYSICAL JOURNAL LETTERS
(2023)
Article
Astronomy & Astrophysics
Anshuman Baruah, Parangam Goswami, Atri Deshamukhya
Summary: In this study, the energy conditions for traversable wormholes in the f(R) gravity model are analyzed, and a wormhole spacetime supporting the null energy condition is numerically obtained. The effects of parameters on the energy conditions are explored.
INTERNATIONAL JOURNAL OF MODERN PHYSICS D
(2022)
Article
Ecology
Kyle E. Coblentz, John P. DeLong
Summary: Evolutionary dynamics are constrained by various limitations, including demographic constraints that restrict evolutionary pathways and possibilities. These constraints can limit the strength of selection, rates of environmental change, and trait values that populations can express. Additionally, demographic and dynamic consequences of evolution can also define ecological boundaries that restrict the pathways populations can traverse. This has important implications for predicting evolutionary dynamics, interpreting past evolution, and understanding the role of stochasticity and ecological constraints on eco-evolutionary dynamics.
Article
Astronomy & Astrophysics
Yun-Long Liu, Zhao-Qing Feng, Xiang-Dong Zhang
Summary: A new polymer black hole solution has been proposed in loop quantum gravity, with the difference from the Schwarzschild black hole being captured by a quantum parameter A. By considering observational constraints from Solar System experiments, effects associated with the parameter A, such as light deflection, Shapiro time delay, and perihelion precession, have been obtained. A parametrized post-Newtonian analysis of this loop quantum gravity black hole has been performed, and the tightest constraint on A has been improved to 0 < A < 4.0 x 10(-6).
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.