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This article investigates the dynamics of charged particles and accretion process around nonlinear charged AdS black holes (BHs). the impact of key factors such as angular momentum, specific energy, and magnetic field on the behavior of particles are focused. Firstly, the concept of the effective potential is examined, which provides insights into the forces acting on particles and the escape velocity they must overcome. The innermost stable circular orbit (ISCO) is also discussed, which is the closest distance a particle can orbit a BH without being pulled in and explore the conditions for particle escape. Next, the energy efficiency and epicyclic frequency of test particles are studied, which measure the amount of energy particle loses due to friction and the frequency of its oscillations, respectively. The accretion processes is analyzed by examining the radial velocity, energy density, and accretion mass of matter falling into the BH. Using the equation of state, how different types of fluid, such as stiff, dust, quintessence and phantom‐like dark energy fluid, affect the accretion process near a BH is investigated. Throughout this study, the parameter k$k$ plays a key role in shaping the dynamics of particles and accretion systems is found. This parameter k$k$ is a measure of the strength of the nonlinear electrodynamics field, and it can have a significant impact on the radius of the ISCO, the energy efficiency of accretion, and other properties. These findings provide new insights into the physics of particle dynamics around nonlinear charged AdS BHs. They could have implications for understanding the behavior of matter in extreme gravitational environments, such as those found near the center of galaxies. This article investigates the dynamics of charged particles and accretion process around nonlinear charged AdS black holes (BHs). The impact of key factors such as angular momentum, specific energy, and magnetic field on the behavior of particles are focused. Firstly, the concept of the effective potential is examined, which provides insights into the forces acting on particles and the escape velocity they must overcome. The innermost stable circular orbit (ISCO) is also discussed, which is the closest distance a particle can orbit a BH without being pulled in and explore the conditions for particle escape. Next, the energy efficiency and epicyclic frequency of test particles are studied, which measure the amount of energy particle loses due to friction and the frequency of its oscillations, respectively. The accretion processes is analyzed by examining the radial velocity, energy density, and accretion mass of matter falling into the BH. Using the equation of state, how different types of fluid, such as stiff, dust, quintessence and phantom‐like dark energy fluid, affect the accretion process near a BH is investigated. Throughout this study, the parameter k plays a key role in shaping the dynamics of particles and accretion systems is found. This parameter k is a measure of the strength of the nonlinear electrodynamics field, and it can have a significant impact on the radius of the ISCO, the energy efficiency of accretion, and other properties. These findings provide new insights into the physics of particle dynamics around nonlinear charged AdS BHs. They could have implications for understanding the behavior of matter in extreme gravitational environments, such as those found near the center of galaxies. [ABSTRACT FROM AUTHOR]

The purpose of this study is to investigate the behavior of charged stellar structures in the f (R , ϕ) theory of gravity, where R denotes the Ricci scalar and ϕ represents the scalar potential, respectively. For our current analysis, we consider Krori–Barua metrics to discuss the spherically symmetric solutions in f (R , ϕ) gravity. We further develop some matching conditions between the spherically symmetric spacetime as interior geometry with Reissner–Nordstrom as exterior geometry. Moreover, we consider the observational data of three distinct stars namely Vela X − 1 , SAX J 1 8 0 8. 4 − 3 6 5 8 and 4 U 1 8 2 0 − 3 0 for present work. We investigate the behavior of energy density, radial pressure, tangential pressure, anisotropic parameter, equation of state parameters, equilibrium condition, sound speeds, Abreu's criteria, adiabatic index and energy conditions respectively. Moreover, we investigate some other properties of the stellar structures including mass-radius relation, compactness factor, and surface redshift. Our investigation reveals that the observed anisotropic findings are physically appropriate and have the highest level of precision in the background of f (R , ϕ) modified theory of gravity. [ABSTRACT FROM AUTHOR]

This paper is devoted to study FRW universe in the context of Chern–Simons corrected f (R) gravity. In particular, the work provides the investigation of cosmological dynamics within modified gravity by assuming a suitable Hubble parameter that might result in a realistic bouncing universe. For this purpose, we consider a suitable Hubble parameter and examine the bouncing cosmology by assuming a well-known f (R) gravity model. Further, we explore the behavior of energy density and pressure profiles by employing the chosen Hubble parameter. We obtain positive and increasing trends of energy density during the bouncing phase while the negative behavior of pressure in our work could potentially be associated with cosmic expansion. We have also studied the energy conditions and in our case NEC is not violated perhaps due to the reason that the equation of state parameter is not crossing the phantom divide. However, the SEC is violated justifying a successful bounce. Moreover, the validation of DEC and TEC suggests that the chosen model is well behaved in nature. The Hubble parameter passing through the bouncing point shows an increasing trend, indicating an expansion phase after the bounce. The equation of state parameter is negative after the bouncing spot, particularly around ω ≈ − 1. This behavior justifies the current cosmic expansion. The deceleration parameter exhibits a negative behavior implies that the cosmological model demonstrates cosmic expansion. Thus all the results validate the existence of a bouncing universe with the chosen model in Chern–Simons corrected f (R) gravity. [ABSTRACT FROM AUTHOR]

In this manuscript, we use the conformal killing vectors to solve the Einstein–Maxwell field equations in the background of modified f (G) gravity. We consider the observational data for four different stars namely P S R J 1614 - 2230 , P S R J 1930 + 327 , C e n X - 3 and V e l a X - 1 respectively. By using the data, we derive the physical parameters from the matching criteria using conformal killing vectors and the exterior Bardeen geometry. Furthermore, several physical properties of compact stellar structures are examined in order to achieve the physical validity and stability for considered models. The graphical analysis including energy density, pressure components, equation of state parameters, and energy conditions are examined. Moreover, the equilibrium conditions through Tolman–Oppenheimer–Volkoff equation and stability criteria through adiabatic index for the charged stellar structure study are investigated. It is worth noting that all of these compact objects are physically viable and stable under conformal motion in context of Bardeen geometry for two different models of f (G) theory of gravity. Conclusively, the results show that f(G) gravity with Bardeen model may provide more massive stellar objects as compared to general relativity. [ABSTRACT FROM AUTHOR]

We propose a logarithmic parametrization form of energy density for the scalar field dark energy in the framework of the standard theory of gravity, which supports the necessary transition from the decelerated to the accelerated behavior of the Universe. The model under consideration is constrained by available observational data, including cosmic chronometers data-sets (CC), Baryonic Acoustic Oscillation (BAO) data-sets, and Supernovae (SN) data-sets, consisting of only two parameters α and β . The combined CC+BAO+SN data-sets yields a transition redshift of z tr = 0. 79 - 0.02 + 0.02 , where the model exhibits signature-flipping and is consistent with recent observations. For the combined data-sets, the present value of the deceleration parameter is calculated to be q 0 = - 0. 43 - 0.06 + 0.06 . Furthermore, the analysis yields constraints on both the parameter density value for matter and the present value of the Hubble parameter, with values of Ω m 0 = 0. 25849 - 0.00025 + 0.00026 and H 0 = 67. 79 - 0.59 + 0.59 km/s/Mpc, respectively, consistent with the results obtained from Planck 2018. Finally, the study investigates how the mass of a black hole evolves over time in a Universe with both matter and dark energy. It reveals that the black hole mass increases initially but stops increasing as dark energy dominates. [ABSTRACT FROM AUTHOR]

In this work, we investigate the thermodynamic properties of black holes (BHs) that have non-trivial topological features in their phase diagrams. We consider three different models of BHs: (1) a class of BHs in dRGT massive gravity, which adds a mass term to general relativity; (2) a class of BHs in 5D Yang–Mills massive gravity, which combines dRGT massive gravity with a non-Abelian gauge field; and (3) a D-dimensional RN-AdS BH surrounded by Quintessence and a cloud of strings, which are strange forms of matter that change the thermodynamics of the BH. Our goal is to find the critical points of these BHs, which provide the location of first-order phase transitions, and figure out their corresponding topological charges. Topological charges are numbers that show how complicated the BH topology is. Then, we look at these BHs as topological defects in the thermodynamic domain, which is the space of thermodynamic variables like pressure and temperature. We calculate winding numbers to analyze topology on a global and local scale at these defects, which are integers that indicate how many times a curve encircling the defect wraps around the origin. Our analysis reveals that the total topological charge is either equal to 0 or 1 for all models, meaning that the BHs have either a trivial or simple topology. In some cases, we see that the BHs' topology belongs to a different thermodynamic topological class. This means that the BHs can go through topological phase transitions. • We investigate the thermodynamic properties of black holes (BHs). • We consider dRGT, Yang–Mills and D-dimensional RN-AdS BH massive gravity models. • We find the critical points of these BHs. • Then, we look at these BHs as topological defects in the thermodynamic domain. • We calculate winding numbers to analyze topology on a global and local scale at these defects. [ABSTRACT FROM AUTHOR]

The aim of this paper is to investigate the field equations of modified --> f (R ,   ϕ) --> theory of gravity, where R and --> ϕ --> represent the Ricci scalar and scalar potential, respectively. We consider the Friedmann–Robertson–Walker space–time for finding some exact solutions by using different values of equation of state parameter. In this regard, different possibilities of the exact solutions have been discussed for dust universe, radiation universe, ultra-relativistic universe, sub-relativistic universe, stiff universe, and dark energy universe. Mainly power law and exponential forms of the scale factor are chosen for the analysis. [ABSTRACT FROM AUTHOR]

• Locally rotationally symmetric Bianchi type-I cosmological models in theory of gravity have been discussed. • Some exact solutions to dark energy and cosmic expansion have been found by employing the power-law model. • Some imperative physical features i. e., pressure, energy density, equation of the state parameter, skewness parameter, and energy conditions have been explored and analyzed graphically • It has been concluded that both of the models are favorable for cosmic expansion. Furthermore, expansion of the universe may be justified in f (R , ϕ) gravity under these models. In this paper, locally rotationally symmetric Bianchi type-I cosmological models in f (R , ϕ) theory of gravity have been investigated, where R and ϕ are Ricci scalar and scalar potential function, respectively. Some exact solutions pertaining to the dark energy and the cosmic expansion have been found by implementing the power law model f (R , ϕ) = λ R m + 1 + β ϕ l + 1 , with λ , m , β and l being the arbitrary real constants, such that m , β ≠ − 1 for the sake of non-triviality. Some important physical attributes like the pressure, energy density, equation of the state parameter, skewness parameter and energy conditions have been studied and analysed graphically. It has been concluded that both of the models are favorable for cosmic expansion. Furthermore, expansion of universe may be justified in f (R , ϕ) gravity under these models. [ABSTRACT FROM AUTHOR]

• The purpose of this paper is to investigate the modified f (R, ϕ, X) theory of gravity, where f (R, ϕ) and X represent the Ricci scalar, scalar potential and kinetic term respectively. • We consider the Friedmann-Robertson-Walker space time for finding solutions of field equations. Furthermore, some numerical solutions are examined by taking Klein-Gordon equation and using different values of equation of state parameter. • The solutions have been discussed for acceleration expansion of universe, dust universe, radiation universe, ultra relativistic universe, sub-relativistic universe and stiff fluid universe. • Moreover their behaviors are examined by using power law and exponential law techniques. It is also concluded that some solution in f (R, ϕ, X) theory of gravity supports the phenomenon of acceleration expansion of the universe. This paper is devoted to investigate the modified f (R) theory of gravity, where R represents the Ricci scalar respectively. For our current work, we consider the Friedmann-Robertson-Walker (FRW) space-time for finding solutions of field equations. Furthermore, some numerical solutions are examined by taking the Klein-Gordon Equation and using distinct values of the equation of state (EoS) parameter. In this way, we have discussed the solutions for acceleration expansion of the Universe, sub-relativistic Universe, radiation Universe, ultra-relativistic Universe, dust Universe, and stiff fluid Universe respectively. Moreover, their behaviours are examined by using power-law and exponential law techniques. The bouncing scenario is also discussed by choosing some particular values of the model parameters and observed the energy conditions, which are satisfied for a successful bouncing model. It is also concluded that some solution in f (R) theory of gravity supports the concept of exotic matter and accelerated expansion of the Universe due to a large amount of negative pressure. [ABSTRACT FROM AUTHOR]

• In this paper, we study three different Bianchi type line elements, like Bianchi type-I (BT-I), Bianchi type-III (BT-III) and Kantowski Sachs space-time in the framework of f (R, ϕ) theory of gravity, where R and ϕ represent the Ricci scalar and the scalar potential function respectively. • We find the exact solution of vacuum field equations of f (R, ϕ) theory by taking valuable assumption that the expansion scalar θ is proportional to the shear scalar σ that is P = Q n. • We analyze that the exact solution satisfied the present cosmic condition of universe and singularity (Big-Bang) is also justified through our evaluated solutions. In this paper, we study three different Bianchi type line elements, like Bianchi type-I (BT-I), Bianchi type-III (BT-III) and Kantowski Sachs space-time in the framework of f (R, ϕ) theory of gravity, where R and ϕ represent the Ricci scalar and the scalar potential function respectively. We find the exact solution of vacuum field equations of f (R, ϕ) theory by taking valuable assumption that the expansion scalar θ is proportional to the shear scalar σ that is P = Q n. We also see some physical parameters like Hubble parameter H , volume scale factor V , average scale factor a , the expansion scalar θ and shear scalar σ for each metric. Finally, we analyze that the exact solution satisfied the present cosmic condition of universe and singularity (Big-Bang) is also justified through our evaluated solutions. [ABSTRACT FROM AUTHOR]