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Separate spin evolution-quantum hydrodynamic (SSE-QHD) model is employed to address the nonlinear propagation of ion-acoustic wave (IAW) and spin electron-acoustic wave (SEAW) in a spin polarized electron-ion plasma. The analysis has been made under the self-consistent field approximation and with exchange correlation effects. The reductive perturbation method (RPM) is used to derive KdV equation and its cnoidal wave solutions. We noted that the phase velocity of IAW in the self-consistent field approximation is almost constant however, in the presence of exchange-correlation potential there is an abrupt change in the phase velocity. The phase velocity of SEAW decreases in the presence of exchange-correlation effects as compare to self-consistent field approximation. We have calculated the condition for the existence of \ nonlinear structures and it is found that \ in the presence of exchange effect the condition satisfy for certain values of $\eta$ at different densities. Furthermore, the comparisons have been made with and without exchange effects, it shows that although the nonlinear profiles of both waves are significantly\ affected with exchange effect but it also converts cnoidal structures of SEAW from rarefactive to compressive. The influence of exchange-correlation potential and spin polarization on the \ profiles of both nonlinear structures is evaluated numerically. The present study may be helpful to understand formation of \ new longitudinal cniondal structures in laboratory degenerate plasma.

The phenomenon by which matter accumulates in the vicinity of a huge celestial object is known as accretion. The gravitational energy is excreted as a consequence of infalling matter onto compact objects. The accretion procedure around celestial bodies like neutron stars, white dwarfs, and black holes has considerable importance because of its ability to transform gravitational energy into radiation. This study investigates the particle's geodesic motion and accretion around the spherically symmetric Reissner-Nordstr\"{o}m black hole coupled with a nonlinear electrodynamics field utilizing isothermal fluid. The formation of the disc-like structure in the accretion process arises from the geodesic motion exhibited by particles near the black hole. The circular orbits, radiant flux energy, radioactive efficiency, and radiant temperature, can be determined. Our study focuses on the examination of particles exhibiting stable circular orbits within the equatorial plane. We analyze the perturbations experienced by particles throughout employing restoring forces and the oscillatory behavior of the particles around a compact object. We conduct an analysis of the fluid's critical flow and maximum accretion rate. Our results show how the black hole parameter $\zeta$ and charge $q$ affect the circular geodesic of particles and the maximum accretion rate of the Reissner-Nordstr\"{o}m black hole coupled with nonlinear electrodynamics., Comment: 14 pages, 8 figures

We demonstrate the investigation of thin accretion disc surrounding the Einstein- Euler-Heisenberg-Anti-de Sitter black hole. Additionally, we analyze the black hole event horizons and compute their effective potential and equations of motion. The specific energy, specific angular momentum, and specific angular velocity of the particles that move in circular orbits above the thin accretion disk are obtained. Also, the effects of parameters of the Einstein- Euler-Heisenberg-Anti de sitter black hole on specific angular velocity, specific heat energy, and specific angular momentum, have been discussed in detail. We display the positions of the innermost stable circular orbits and illustrate the effective potential. Furthermore, the circular orbits of black hole are obtained numerically and locates the position of the innermost stable circular orbit and event horizon. Also, we study the Gamma ray burst emitted from the Einstein Euler-Heisenberg Anti de sitter black hole., Comment: 19 Pages, 24 Eps figures, Accepted for publication in Fortschritte der Physik - Progress of Physics

This paper deals with astrophysical accretion onto the magnetically charged Euler-Heisenberg black holes with scalar hair. We examine the accretion process of a variety of perfect fluids, including polytropic and isothermal fluids of the ultra-stiff, ultra-relativistic, and sub-relativistic forms, when fluid is accreting in the vicinity of the black hole. By using the Hamiltonian dynamical approach, we can find the sonic or critical points numerically for the various types of fluids that are accreting onto the black hole. Furthermore, for several types of fluids, the solution is provided in closed form, expressing phase diagram curves. We compute the mass accretion rate of a magnetically charged Euler-Heisenberg black hole with scalar hair. We observe that the maximum accretion rate is attained for small values of the black hole parameters. We may be able to understand the physical mechanism of accretion onto black holes using the outcomes of this investigation., Comment: 16 pages, 7 figures, and 6 tables; v2: version published in EPJC

In this paper, we study thermodynamics, thermal fluctuations, phase transitions and the charged anti-de Sitter black hole surrounded by perfect fluid dark matter. Large black holes are shown to be stable when subject to thermal fluctuations, and we begin by exploring how these fluctuations affect the uncorrected thermodynamic quantities of entropy, Helmholtz free energy, Gibbs free energy, enthalpy specific heat, and phase transition stability. We also discuss null geodesics and the radius of the photon sphere for the charged AdS BH and use the radius of a photon sphere to calculate the Lyapunov exponent and angular velocity. Exceptionally, we test the effects of various parameters of a black hole graphically by observing the existence of the correction parameter and the coupling parameter, which reveal the behavior of corrected thermodynamic quantities. Lastly, we see how the system is stable (under the effects of the dark matter parameter) by figuring out the specific heat and Hawking temperature, which are both related to entropy., Comment: 31 Pages, 41 EPS figure, accepted for Publication in EPJC

In this paper, we have introduced new viable solutions of Einstein-Maxwell field equations by incorporating the features of anisotropic matter distribution in the realm of General theory of Relativity ($GR$). For this procurement, we have employed a Finch-Skea spacetime along with a generalized polytropic equation of state ($EoS$). We have constructed various models of generalized polytropes by assuming the different choices of the polytropic index i.e.,$\eta=\frac{1}{2}, \frac{2}{3}, 1$ and $2$. The numerous physical characteristics of these considered models have been studied via graphical analysis, which obey all the essential conditions of the astrophysical compact objects. Furthermore, such outcomes of charged anisotropic compact star models can be regained to the various cases such as linear, quadratic and polytropic $EoS$., Comment: 31 Pages, 11 Figures, 1 Table. Published in Chinese Phys. C

This paper deals with the thermodynamical properties of black hole formulated in Einstein theory of relativity and associated with a nonlinear electromagnetic field. The transition of the black hole is analyzed using the parameters mass, electric charge, coupling constant, and cosmological constant. We find-out the thermodynamical aspects of exact black hole solutions to compute the black hole mass, temperature, entropy, Gibbs free energy, specific heat and the critical exponents in the phase space. Further, we study the stability of the black hole solution by specific heat and Gibbs free energy. We look at the first and second phase changes and show a P-V criticality, which is like the Van der Waals phase change. We also examine the equation of the state and the critical exponents., Comment: 17 Pages, 21 Figures , To be published in Chinese Phys. C

The accretion of matter onto celestial bodies like black holes and neutron stars is a natural phenomenon that releases up to $40\%$ of the matter's rest-mass energy, which is considered a source of radiation. In active galactic nuclei and X-ray binaries, huge luminosities are observed as a result of accretion. Using isothermal fluid, we examine the accretion and geodesic motion of particles in the vicinity of a spherically symmetric black hole spacetime in the Einstein-$SU(N)$ non-linear sigma model. In the accretion process, the disk-like structure is produced by the geodesic motion of particles near the black hole. We determine the innermost stable circular orbit, energy flux, radiation temperature, and radioactive efficiency numerically. In the equatorial plane, we investigate the mobility of particles with stabilities that form circular orbits. We examine perturbations of a test particle by using restoring forces and particle oscillations in the vicinity of the black hole. We analyze the maximum accretion rate and critical flow of the fluid. Our findings demonstrate how parameter $N$ influences the circular motion of a test particle as well as the maximum accretion rate of the black hole in the Einstein-$SU(N)$ non-linear sigma model., Comment: 28 pages, 10 figures; v2: 14 pages, version appeared in EPJC

The very latest observation of $M87$ supermassive black hole (BH) by the Event Horizon Telescope (EHT) provides the accretion onto BHs is an interesting study in the theory of gravity. We study the geodesics structure and accretion near a nonlinear electrodynamics BH in strong and weak field approximations. These approximations provide the disc-like structure under the geodesic motion and accretion around the BH. Near the equatorial plane, we provide some new reasons to make circular orbits and accretion of test particles around the BH. Then we investigate perturbations, the critical speed of the fluid and the mass accretion rate of particles around the central object. The physical validity of this study shows that the parameter $\beta$ and $Q$ play an important role in the circular orbits and the mass accretion rate in strong and weak field approximations., Comment: 22 pages, 13 figures

The accretion of test fluids flowing onto a black hole is investigated. Particularly, by adopting a dynamical Hamiltonian approach, we are capable to find the critical points for various cases of black hole in conformal gravity. In these cases, we have analyzed the general solutions of accretion employing the isothermal equations of state. The steady state and spherically symmetric accretion of different test fluids onto the conformal gravity black hole has been considered. Further, we have classified these flows in the context of equations of state and the cases of conformal gravity black hole. The new behavior of polytropic fluid accretion is also discussed in all three cases of black hole. Black hole mass accretion rate is the most important part of this research in which we have investigated that the Schwarzschild black hole produce a typical signature than the conformal gravity black hole and Schwarzschild de-Sitter black hole. The critical fluid flow and the mass accretion rate have been presented graphically by the impact parameters $\beta$, $\gamma$, $k$ and these parameters have great significance. Additionally, the maximum mass rate of accretion fall near the universal and Killing horizons and minimum rate of accretion occurs in between these regions. Finally, the results are compared with the different cases of black hole available in the literature., Comment: 36 pages, 33 figures, accepted for publications in EPJC

In this work, a systematic study, examining the propagation of periodic and solitary wave along the magnetic field in a cold collision-free plasma, is presented. Employing the quasi-neutral approximation and the conservation of momentum flux and energy flux in the frame co-traveling with the wave, the exact analytical solution of the stationary solitary pulse is found analytically in terms of particle densities, parallel and transverse velocities, as well as transverse magnetic fields. Subsequently, this solution is generalized in the form of periodic waveforms represented by cnoidal-type waves. These considerations are fully analytical in the case where the total angular momentum flux $L$, due to the ion and electron motion together with the contribution due to the Maxwell stresses, vanishes. A graphical representation of all associated fields is also provided.

The ambition of the present work is to highlight the phenomena of strong gravitational lensing and deflection angle for the photons coupling with Weyl tensor in a Kiselev black hole. Here, we have extended the prior work of Chen and Jing \cite{1} for Schwarzschild black hole to Kiselev black hole. For this purpose, the equation of motion for the photons coupled to Weyl tensor, null geodesic and equation of photon sphere in a Kiselev black hole spacetime have been formulated. It is found that the equation of motion of the photons depends not only on the coupling between photon and Weyl tensor, but also on the polarization direction of the photons. There is a critical value of the coupling parameter $\alpha$ for existence of the marginally circular photon orbit outside the event horizon, which depends on the parameters of black hole and the polarization direction of photons. Further, the polarization directions of coupled photon and the coupling parameter $\alpha$, both modify the features of the photon sphere, the angle of deflection and the functions $(\bar{a}$ and $\bar{b})$ for the strong gravitational lensing in Kiselev black hole spacetime. In addition to this, the observable gravitational lensing quantities and the shadows of the Kiselev black hole spacetime are presented in detail., Comment: 26 pages, 10 figures, major revision included and accepted for publications in Chinese Physics C. arXiv admin note: text overlap with arXiv:1611.08783, arXiv:1502.01088 by other authors

In this outline we recognize the idea of complexity factor for static anisotropic self-gravitating source with generalized $f(R)$ metric gravity theory. In present consideration, we express the Einstein field equations, hydrostatic equilibrium equation, the mass function and physical behavior of $f(R)$ model by using some observational data of well known compact stars like $4U~1820-30, SAX~J1808.4-3658$ and $Her~X-1$. We define the scalar functions through the orthogonal splitting of the Reimann-Christofell tensor and then find the vanishing complexity condition for self-gravitating system with the help of these scalars. It has been found that the vanishing condition for the complexity are pressure anisotropy and energy density inhomogeneity must cancel each other. Moreover, we study the momentous results of an astral object for the vanishing of complexity factor. Finally, these solutions reduced to previous investigation about complexity factor in General Relativity by taking $\lambda=0$., Comment: 20 pages, 5 Figures, 1 Table, Accepted for Publication in Eur. Physical Journal C

In the present work, we study a new model of anisotropic compact stars in the regime of Rastall theory. To solve the Rastall field equations we have used the Karori and Barua (KB) ansatz along with the quintessence dark energy characterized by a parameter $\omega_{q}$ with $-1<\omega_{q}<-\frac{1}{3}$. We present a comparative study to demonstrate the physical acceptance of our proposed model. We compare the numerical values of physical parameters obtained from our model with those of general relativity ($GR$) model given by Bhar \cite{1} and observe that our model is more compatible (for some chosen values of Rastall dimensionless parameter $\gamma=\kappa\lambda$) with observational data than $GR$ model. For this analysis we have consider four different compact stars, $SAX J1808-3658 (SSI)$, $4U 1820-30$, $Vela X-12$ and $PSR J1416-2230$ with radii $7.07km$, $10km$, $9.99km$ and $10.3km$, respectively. In this investigation we also present some physical aspects of the proposed model necessary to check the validity of the model and inferred that our model is acceptable physically and geometrically., Comment: 20 pages, 16 figures, 8 tables, Accepted for Publication in Eur. Physical Journal A

In this paper, we have studied gravitational collapse and expansion of non-static anisotropic fluid in $5D$ Einstein Gauss-Bonnet gravity. For this purpose, the field equations have been modeled and evaluated for the given source and geometry. The two metric functions have been expressed in terms of parametric form of third metric function. We have examined the range of parameter $\beta$ (appearing in the form of metric functions) for which $\Theta$ the expansion scalar becomes positive/negative leads to expansion/collapse of the source. The trapped surface condition has been explored by using definition of Misner-Sharp mass and auxiliary solutions. The auxiliary solutions of the field equations involve a single function which generates two types of anisotropic solutions. Each solution can be represented in term of arbitrary function of time, this function has been chosen arbitrarily to fit the different astrophysical time profiles. The existing solutions forecast gravitational expansion and collapse depending on the choice of initial data. In this case, it has been investigated wall to wall collapse of spherical source. The dynamics of the spherical source has been observed graphically with the effects of Gauss-Bonnet coupling term $\alpha$ in the case of collapse and expansion. The energy conditions are satisfied for the specific values of parameters in the both solutions, this implies that the solutions are physically acceptable., Comment: 20 pages,16 Figures, Title Changed, Major revision included,accepted version to appear in Adv.High Energy Physics

In a recent paper, Herrera \cite{2} (L. Herrera: Phys. Rev. D97, 044010(2018)) have proposed a new definition of complexity for static self-gravitating fluid in General Relativity. In the present article, we implement this definition of complexity for static self-gravitating fluid to case of $f(R)$ gravity. Here, we found that in the frame of $f(R)$ gravity the definition of complexity proposed by Herrera, entirely based on the quantity known as complexity factor which appears in the orthogonal splitting of the curvature tensor. It has been observed that fluid spheres possessing homogenous energy density profile and isotropic pressure are capable to diminish their the complexity factor. We are interested to see the effects of $f(R)$ term on complexity factor of the self-gravitating object. The gravitating source with inhomogeneous energy density and anisotropic pressure have maximum value of complexity. Further, such fluids may have zero complexity factor if the effects of inhomogeneity in energy density and anisotropic pressure cancel the effects of each other in the presence of $f(R)$ dark source term. Also, we have found some interior exact solutions of modified $f(R)$ field equations satisfying complexity criterium and some applications of this newly concept to the study of structure of compact objects are discussed in detail. It is interesting to note that previous results about the complexity for static self-gravitating fluid in General Relativity can be recovered from our analysis if $f(R)=R$, which General Relativistic limit of $f(R)$ gravity. Some future research directions have been mentioned in the end of the summary., Comment: 16 pages, no figure accepted for publication in EPJC

The plan of this study is to inspect the effects of dynamics of dissipative gravitational collapse in cylindrical symmetric non-static spacetime by using Misner-Sharp concept in context of metric $f(R)$ theory of gravity. For more generic isotropic fluid distribution of cylindrical object by dissipative nature of dark source of the fluid due to energy matter tensor,the Misner-Sharp approach technique has been used to illustrate the heat flux with free radiating out flow, bulk and shear viscosity. Furthermore, dynamical equation have been associated with full casual heat transportation equations in framework of $M\ddot{u}ller$-Israel-Stewart formalism. The present study explain the effects of thermodynamics viscid/heat radiating coupling factors on gravitational collapse in $M\ddot{u}ller$-Israel-Stewart notion and matches with the consequences of prior astrophysicists by excluding such coefficients and viscosity variables., Comment: 22 pages, No figure, submitted for publication

The aim of this paper is to investigate the dynamical aspects of charged viscous cylindrical source by using Misner approach. To this end, we have considered the more general charged dissipative fluid enclosed by the cylindrical symmetric spacetime. The dissipative nature of the source is due to the presence of dissipative variables in the stress-energy tensor. The dynamical equations resulting from such charged cylindrical dissipative source have been coupled with the causal transport equations for heat flux, shear and bulk viscosity, in the context of Israel-Steward theory. In this case, we have the considered the Israel-Steward transportation equations without excluding the thermodynamics viscous/heat coupling coefficients. The results are compared with the previous works in which such coefficients were excluded and viscosity variables do not satisfy the casual transportation equations., Comment: 16 Pages, no figures, accepted for publication in EPJA

In this paper, we discuss spherically symmetric wormhole solutions in $f(R,T)$ modified theory of gravity by introducing well-known non-commutative geometry in terms of Gaussian and Lorentizian distributions of string theory. For some analytic discussion, we consider an interesting model of $f(R,T)$ gravity defined by $f(R,T)=f_{1}(R)+\lambda T$. By taking two different choices for the function $f_{1}(R)$, that is, $f_{1}(R)=R$ and $f_{1}(R)=R+\alpha R^{2}+\gamma R^{n}$, we discuss the possible existence of wormhole solutions. In the presence of non-commutative Gaussian and Lorentizian distributions, we get exact and numerical solutions for both these models. By taking appropriate values of the free parameters, we discuss different properties of these wormhole models analytically and graphically. Further, using equilibrium condition, it is found that these solutions are stable. Also, we discuss the phenomenon of gravitational lensing for the exact wormhole model and it is found that the deflection angle diverges at wormhole throat., Comment: 15 pages, 18 figures

The Einstein Gauss-Bonnet theory of gravity is the low energy limit of heterotic super-symmetric string theory. This paper deals gravitational collapse of perfect fluid in Einstein Gauss-Bonnet gravity by considering the Lemaitre - Tolman - Bondi metric. For this purpose, the closed form of exact solution of equations of motion has been determined by using the conservation of stress-energy tensor and the condition of marginally bound shells. It has been investigated that the presence of Gauss-Bonnet coupling term $\alpha>0$ and pressure of the fluid modifies the structure and time formation of singularity. In this analysis singularity form earlier than horizon, so end state of the collapse is a naked singularity depending on the initial data. But this singularity is weak and timelike that goes against the investigation of general relativity., Comment: 16 pages, 3 Figures; some future research directions mentioned; to appear in European Physical Journal C

In this paper, we have formulated the exact solutions of the non-static anisotropic gravitating source in $f(R,T)$ gravity which may lead to expansion and collapse. By assuming the no thermal conduction in gravitating source, we have determine parametric solutions in $f(R,T)$ gravity with non-static spherical geometry filled with anisotropic fluid. We have examined the range of parameter for which expansion scalar become negative and positive leading to collapse and expansion, respectively. Further, using the definition of mass function the condition for the trapped surface have been explored and it has been investigated there exists a single horizon in this case. The impact of coupling parameter $\lambda$ has been discussed in detail in both cases. For the various values of coupling parameter $\lambda$, we have plotted energy density, anisotropic pressure and anisotropic parameter in case of collapse and expansion. The physical significance of the graphs has been explained in detail., Comment: 18 Pages, 8 Figures, Accepted for Publication in European Physical Journal C

This paper is about the $n+2$-dimensional gravitational contraction of inhomogeneous fluid without heat flux in the framework of $f(R)$ metric theory of gravity. Matching conditions for two regions of a star has been derived by using the Darmois junction conditions. For the analytic solution of equations of motion in modified $f(R)$ theory of gravity, we have taken scalar curvature as constant. Hence final result of gravitational collapse in this frame work is the existence of black hole and cosmological horizons, both of these form earlier than singularity. It has been shown that constant curvature term $f(R_{0})$ ($R_0$ is constant scalar curvature) slows down the collapsing process., Comment: 17 Pages, to appear in European Physical Journal C

In this paper, we investigate the Hawking radiation process as a semiclassical quantum tunneling phenomenon from black ring and Myers-Perry black holes in 5-dimensional (5D) spaces. Using Lagrangian of Glashow-Weinberg-Salam model with background electromagnetic field (for charged W-bosons) and the WKB approximation, we will evaluate the tunneling rate/probability of charged vector particles through horizons by taking into account the electromagnetic vector potential. Moreover, we investigate the corresponding Hawking temperature values by considering Boltzmann factor for both cases and analyze the whole spectrum generally., Comment: 24 pages, no figures, submitted for publication

In this paper, we have explored the effects of dissipation on the dynamics of charged bulk viscous collapsing cylindrical source which allows the out follow of heat flux in the form of radiations. Misner-Sharp formulism has been implemented to drive the dynamical equation in term of proper time and radial derivatives. We have investigated the effects of charge and bulk viscosity on the dynamics of collapsing cylinder. To determine the effects of radial heat flux, we have formulated the heat transport equations in the context of M$\ddot{u}$ller-Israel-Stewart theory by assuming that thermodynamics viscous/heat coupling coefficients can be neglected within some approximations. In our discussion, we have introduced the viscosity by the standard (non-casual) thermodynamics approach. The dynamical equations have been coupled with the heat transport equation equation, the consequences of resulting coupled heat equation have been analyzed in detail., Comment: 17 Pages, no figure

The aim of this paper is to study the quantum tunneling process for charged vector particles through the horizons of black holes by using Proca equation. For this purpose, we have consider a pair of charged accelerating and rotating black holes with NUT parameter and a black hole in $5D$ gauged supergravity, respectively. Further, we have studied the tunneling probability and corresponding Hawking temperature for both black holes by using WKB approximation., Comment: 17 Pages. Title modified and minor corrections. Submitted for Publications