This paper investigates wormhole solutions within the framework of extended symmetric teleparallel gravity,incorporating non-commutative geometry,and conformal symmetries.To achieve this,we examine the linear wormhole...This paper investigates wormhole solutions within the framework of extended symmetric teleparallel gravity,incorporating non-commutative geometry,and conformal symmetries.To achieve this,we examine the linear wormhole model with anisotropic fluid under Gaussian and Lorentzian distributions.The primary objective is to derive wormhole solutions while considering the influence of the shape function on model parameters under Gaussian and Lorentzian distributions.The resulting shape function satisfies all the necessary conditions for a traversable wormhole.Furthermore,we analyze the characteristics of the energy conditions and provide a detailed graphical discussion of the matter contents via energy conditions.Additionally,we explore the effect of anisotropy under Gaussian and Lorentzian distributions.Finally,we present our conclusions based on the obtained results.展开更多
In this paper,the non-static solutions for perfect fluid distribution with plane symmetry in f(R,T)gravitational theory are obtained.Firstly,using the Lie symmetries,symmetry reductions are performed for considered ve...In this paper,the non-static solutions for perfect fluid distribution with plane symmetry in f(R,T)gravitational theory are obtained.Firstly,using the Lie symmetries,symmetry reductions are performed for considered vector fields to reduce the number of independent variables.Then,corresponding to each reduction,exact solutions are obtained.Killing vectors lead to different conserved quantities.Therefore,we figure out the Killing vector fields corresponding to all derived solutions.The derived solutions are further studied and it is observed that all of the obtained spacetimes,at least admit to the minimal symmetry group which consists of δ_(y),δ_(z) and -zδ_(y)+yδ_(z).The obtained metrics,admit to 3,4,6,and 10,Killing vector fields.Conservation of linear momentum in the direction of y and z,and angular momentum along the x axis is provided by all derived solutions.展开更多
This study aims to discuss anisotropic solutions that are spherically symmetric in the quintessence field,which describe compact stellar objects in the modified Rastall teleparallel theory of gravity.To achieve this g...This study aims to discuss anisotropic solutions that are spherically symmetric in the quintessence field,which describe compact stellar objects in the modified Rastall teleparallel theory of gravity.To achieve this goal,the Krori and Barua arrangement for spherically symmetric components of the line element is incorporated.We explore the field equations by selecting appropriate off-diagonal tetrad fields.Born-Infeld function of torsion f(T)=β√λT+1-1 and power law form h(T)=δTn are used.The Born-Infeld gravity was the first modified teleparallel gravity to discuss inflation.We use the linear equation of state pr=ξρto separate the quintessence density.After obtaining the field equations,we investigate different physical parameters that demonstrate the stability and physical acceptability of the stellar models.We use observational data,such as the mass and radius of the compact star candidates PSRJ 1416-2230,Cen X-3,&4U 1820-30,to ensure the physical plausibility of our findings.展开更多
To obtain analytically relativistic quintessence anisotropic spherical solutions in the f(T)paradigm is the primary objective of this paper.To do this,the pressure anisotropy condition is imposed,and we employ a metri...To obtain analytically relativistic quintessence anisotropic spherical solutions in the f(T)paradigm is the primary objective of this paper.To do this,the pressure anisotropy condition is imposed,and we employ a metric potential of the Tolman–Kuchowicz(TK)type.We also suppose that our current model incorporates a quintessence field characterized by a parameterωq,in addition to the anisotropic matter distribution.In the presence of the parameterα,the field equations are modified by the choice of the f(T)function.The f(T)gravity parameterαadds new components to the basic physical characteristics,such as density,pressure,subliminal sound velocity,surface redshift,etc,of the present model.By selecting the compact star Her X-1 and varyingαfrom 0.5 to 2.5,we examined all the physical characteristics of the model parameter of the configuration.The graphical process demonstrates that a more compact item is produced with greater values ofα.The hydrostatic equilibrium condition of the model is discussed,as well as the mass-radius relationship for our current model is obtained.展开更多
In this paper,we classify static spherically symmetric(SS)perfect fluid space-times via conformal vector fields(CVFs)in f(T)gravity.For this analysis,we first explore static SS solutions by solving the Einstein field ...In this paper,we classify static spherically symmetric(SS)perfect fluid space-times via conformal vector fields(CVFs)in f(T)gravity.For this analysis,we first explore static SS solutions by solving the Einstein field equations in f(T)gravity.Secondly,we implement a direct integration technique to classify the resulting solutions.During the classification,there arose 20 cases.Studying each case thoroughly,we came to know that in three cases the space-times under consideration admit proper CVFs in f(T)gravity.In one case,the space-time admits proper homothetic vector fields,whereas in the remaining 16 cases either the space-times become conformally flat or they admit Killing vector fields.展开更多
In this paper,we study a theory of gravity called mimetic f(R,T)in the presence of swampland dS conjecture.For this purpose,we introduce several inflation solutions of the Hubble parameter H(N)from f(R,T)=R+δT gravit...In this paper,we study a theory of gravity called mimetic f(R,T)in the presence of swampland dS conjecture.For this purpose,we introduce several inflation solutions of the Hubble parameter H(N)from f(R,T)=R+δT gravity model,in which R is Ricci scalar,and T denotes the trace of the energy–momentum tensor.Also,δand N are the free parameter and a number of e-fold,respectively.Then we calculate quantities such as potential,Lagrange multiplier,slow-roll,and some cosmological parameters such as nsand r.Then we challenge the mentioned inflationary model from the swampland dS conjecture.We discuss the stability of the model and investigate the compatibility or incompatibility of this inflationary scenario with the latest Planck observable data.展开更多
Some recent developments(accelerated expansion)in the Universe cannot be explained by the conventional formulation of general relativity.We apply the recently proposed f(T,B)gravity to investigate the accelerated expa...Some recent developments(accelerated expansion)in the Universe cannot be explained by the conventional formulation of general relativity.We apply the recently proposed f(T,B)gravity to investigate the accelerated expansion of the Universe.By parametrizing the Hubble parameter and estimating the best fit values of the model parameters b_(0),b_(1),and b_(2)imposed from Supernovae type la,Cosmic Microwave Background,B aryon Acoustic Oscillation,and Hubble data using the Markov Chain Monte Carlo method,we propose a method to determine the precise solutions to the field equations.We then observe that the model appears to be in good agreement with the observations.A change from the deceleration to the acceleration phase of the Universe is shown by the evolution of the deceleration parameter.In addition,we investigate the behavior of the statefinder analysis,equation of state(EoS)parameters,along with the energy conditions.Furthermore,to discuss other cosmological parameters,we consider some wellknown f(T,B)gravity models,specifically,f(T,B)=aT^(b)+cB^(d).Lastly,we find that the considered f(T,B)gravity models predict that the present Universe is accelerating and the EoS parameter behaves like the ACDM model.展开更多
We report a viable exponential gravity model for the accelerated expansion of the universe in Bianchi VI<sub>h</sub> space-time. By considering the estimated physical parameters, the cosmological models ar...We report a viable exponential gravity model for the accelerated expansion of the universe in Bianchi VI<sub>h</sub> space-time. By considering the estimated physical parameters, the cosmological models are constructed and analyzed in detail. We found that the state parameter in both the models increases to a higher negative range in an early epoch of the phantom domain and it goes to the positive domain at a late phase of the evolution. The effective cosmological constant remains in a positive domain for both models, which is a good sign of accelerating expansion of the universe.展开更多
This study explores the f(R,T)gravity theory,which introduces a coupling between matter and curvature,through the simplest linear functional form f(R,T)=R+2βT.We derive the modified Einstein field equations and conse...This study explores the f(R,T)gravity theory,which introduces a coupling between matter and curvature,through the simplest linear functional form f(R,T)=R+2βT.We derive the modified Einstein field equations and conservation equations for this theory and then apply this framework to study the structural properties of quark stars(QSs)composed of interacting quark matter,considering perturbative QCD corrections and color superconductivity.By solving the modified Tolman-Oppenheimer-Volkoff equations,we investigate the mass-radius relation,stability criteria,and energy conditions of QSs.Our results indicate that the f(R,T)gravity significantly influences the properties of QSs,leading to deviations from General Relativity.The analysis is consistent with recent observational data,suggesting that the modified gravity framework could provide viable models for the study of compact stars.展开更多
We investigated the impact of f(R,L_(m),T)gravity on the internal structure of compact stars,expecting this theory to manifest prominently in the high-density cores of such stars.We considered the algebraic function,f...We investigated the impact of f(R,L_(m),T)gravity on the internal structure of compact stars,expecting this theory to manifest prominently in the high-density cores of such stars.We considered the algebraic function,f(R,L_(m),T)=R+αTL_(m),whereαrepresents the matter-geometry coupling constant.We specifically chose the matter Lagrangian density L_(m)=-ρto explore compact stars with anisotropic pressure.To this end,we employed the MIT bag model as an equation of state.Subsequently,we numerically solved the hydrostatic equilibrium equations to obtain mass-radius relations for quark stars(QSs),examining static stability criteria,adiabatic index,and speed of sound.Finally,we used recent astrophysical data to constrain the coupling parameterα,which may lead to either larger or smaller masses for QSs,compared to their counterparts in general relativity.展开更多
In this paper,we use genetic algorithms,a specific machine learning technique,to achieve a model-independent reconstruction of f(T)gravity.By using H(z)data derived from cosmic chronometers and the radial Baryon Acous...In this paper,we use genetic algorithms,a specific machine learning technique,to achieve a model-independent reconstruction of f(T)gravity.By using H(z)data derived from cosmic chronometers and the radial Baryon Acoustic Oscillation method,including the latest Dark Energy Spectroscopic Instrument(DESI)data,we reconstruct the Hubble rate,which is the basis parameter for reconstructing f(T)gravity without any assumptions.In this reconstruction process,we use the current value of the Hubble rate,H_(0),derived by genetic algorithms.The reconstructed f(T)function is consistent with the standardΛCDM cosmology within the 1 confidence level across a broad temporal range.The mean f(T)curve,adopting a quadratic form,prompts us to parametrize it using a second-degree polynomial.This quadratic deviation from theΛCDM scenario is mildly favored by the data.展开更多
In this paper,we investigate the topological charge and conditions for the existence of the photon sphere in Kiselev-anti-de Sitter(AdS)black holes within f(R,T)gravity.Furthermore,we establish their topological class...In this paper,we investigate the topological charge and conditions for the existence of the photon sphere in Kiselev-anti-de Sitter(AdS)black holes within f(R,T)gravity.Furthermore,we establish their topological classifications.We employ two different methods based on Duan's topological current p-mapping theory viz analysis of temperature and the generalized Helmholtz free energy methods to study the topological classes of our black hole.Considering this black hole,we discuss the critical and zero points(topological charges and topological numbers)for different parameters.Our findings reveal that the Kiselev parameter o and f(R,T)gravity parameter y influence the number of topological charges of black holes,providing novel insights into topological classifications.We observe that for given values of the free parameters,total topological charges(Q_(total)=-1)exist for the T method and total topological numbers(ω=+1)for the generalized Helmholtz free energy method.Our research findings elucidate that,in contrast to the scenario in whichω=1/3,in other cases,increasing y increases the number of total topological charges for the black hole.Interestingly,for the phantom field(ω=-4/3),we observe that decreasingγincreases the number of topological charges.Additionally,we study the results for the photon sphere.The studied models reveal that the simultaneous presence ofγandωeffectively expands the permissible range forγ.In other words,the model can exhibit black hole behavior over a larger domain.Additionally,we observe that with the stepwise reduction ofγ,the region covered by singularity diminishes and becomes more restricted.However,an interesting point about all three ranges is the elimination of the forbidden region in this model.In other words,this model and the investigated areas appear to have no region in which both theφand metric functions simultaneously lack solutions.Additionally,we fully check the curvatures singularities and energy conditions for the mentioned black hole.展开更多
We explored two f(R,T)gravity models and derived black hole solutions within these models.We focus on investigating how the f(R,T)model influences the thermodynamic characteristics of black holes by studying their the...We explored two f(R,T)gravity models and derived black hole solutions within these models.We focus on investigating how the f(R,T)model influences the thermodynamic characteristics of black holes by studying their thermodynamic topology and thermodynamic geometry.We consid-ered five specific values of the thermodynamic parameter w,which signify five different classes of black hole solutions in general relativity(GR).We observed significant changes in the local topological properties of these black holes compared to GR,depending on the model parameters.Notably,we identified an additional topological class W=O for some values of w that is absent in the GR framework.We also studied the ther-modynamic geometry of the black hole using the Geometrothermodynam-ics(GTD)formalism.Our analysis demonstrates that the singular point,where the GTD scalar curvature diverges,corresponds exactly to the point where the heat capacity changes sign.Additionally,we constrained the model parameters of both models considered by utilizing black hole shadow data from the Sgr A*black hole,measured by the Event Horizon Telescope(EHT).展开更多
This paper presents a picture of compact structures for the f(R,T)model of the form R+γe^χT,withγandχbeing parameters.The poly tropic equation of state and the MIT bag model reflect the pressure density relation f...This paper presents a picture of compact structures for the f(R,T)model of the form R+γe^χT,withγandχbeing parameters.The poly tropic equation of state and the MIT bag model reflect the pressure density relation for these compact objects.For this purpose,a system of two differential equations involving pressure as well as the mass of the stellar structure is obtained from field equations and the Tolman-Oppenheimer-Volkoff(TOV)equation.The numerical solution of this system gives a graphical description of various characteristics of these compact systems.To examine the viability and stability of assumed configurations,the energy conditions,causality relation and adiabatic index are discussed for the presumed scenario.展开更多
Dark energy is typically the principal component needed for the traversability of wormholes(WH),as it provides the negative gravity effect required to keep the throat open.However,can this be achieved without dark ene...Dark energy is typically the principal component needed for the traversability of wormholes(WH),as it provides the negative gravity effect required to keep the throat open.However,can this be achieved without dark energy?It turns out that if we couple the trace of energy-momentum with the standard Einstein-Hilbert Lagrangian and utilize a specific equation of state(EoS),dark energy may be obviated.The Casimir stress energy is known to result in the violation of the null energy condition(NEC)on the energy momentum tensor.This phenomenon makes such an EoS an ideal candidate for generating traversable WH geometries.The laboratory proven phenomenon provides a natural mechanism to sustain an open WH throat without relying on dark energy.Therefore,we generate two classes of WH solutions using this in energy-momentum trace-coupling gravity.For the specific choice of the Casimir EoS relating the energy-momentum tensor components[Kar and Sahdev:Phys.Rev.D 52,2030(1995)]and different choices of redshift functions,we determine the WH geometry completely.The obtained WH solutions violate the NECs,and all qualitative constraints demanded for physically realizable WHs are satisfied.This is demonstrated via graphical plots for a suitably chosen range of coupling parameter values.Furthermore,our study investigates the repulsive effect of gravity,revealing that its presence leads to a negative deflection angle for photons traveling along null geodesics.Notably,we observe a consistent pattern of negative values for the deflection angle across all values of r_(0) in the three scenarios considered,thus indicating the clear manifestation of the repulsive gravity effect.All of this is possible without invoking the existence of dark energy.展开更多
In this study,we conduct an analysis of traversable wormhole solutions within the framework of linear f(Q,T)=αQ+βT gravity,ensuring that all energy conditions hold for the entire spacetime.The solutions presented in...In this study,we conduct an analysis of traversable wormhole solutions within the framework of linear f(Q,T)=αQ+βT gravity,ensuring that all energy conditions hold for the entire spacetime.The solutions presented in this paper are derived through a comprehensive analytical examination of the parameter space associated with the wormhole model.This involves considering the exponents governing the redshift and shape functions,as well as the radius of the wormhole throat(r_(0)),the redshift function value at the throat(∅_(0)),and the model parameters(αandβ).Moreover,we establish bounds on these free parameters,which guarantee the satisfaction of the energy conditions throughout spacetime and also provide two solutions.Furthermore,we use the Israel junction condition to observe the stability of a thin-shell around the wormhole.Finally,we calculate the null energy condition criteria as well as the potential for the thin-shell and how it varies with the chosen shape function.展开更多
In this study,we obtain wormhole solutions in the recently proposed extension of symmetric teleparallel gravity,known as f(Q,T)gravity.Here,the gravitational Lagrangian L is defined by an arbitrary function f of Q and...In this study,we obtain wormhole solutions in the recently proposed extension of symmetric teleparallel gravity,known as f(Q,T)gravity.Here,the gravitational Lagrangian L is defined by an arbitrary function f of Q and T,where Q is a non-metricity scalar,and T is the trace of the energy-momentum tensor.In this study,we obtain field equations for a static spherically symmetric wormhole metric in the context of general f(Q,T)gravity.We study the wormhole solutions using(ⅰ)a linear equation of state and(ⅱ)an anisotropy relation.We adopt two different forms of f(Q,T),(a)linear f(Q,T)=αQ+βT and(b)non-linear f(Q,T)=Q+λQ^(2)+ηT,to investigate these solutions.We investigate various energy conditions to search for preservation and violation among the obtained solutions and find that the null energy condition is violated in both cases of our assumed forms of f(Q,T).Finally,we perform a stability analysis using the Tolman-Oppenheimer-Volkov equation.展开更多
This work suggests a new model for anisotropic compact stars with quintessence in f(T)gravity by us-ing the off-diagonal tetrad and the power-law as f(T)=βT^(n),where T is the scalar torsion andβand n are real con-s...This work suggests a new model for anisotropic compact stars with quintessence in f(T)gravity by us-ing the off-diagonal tetrad and the power-law as f(T)=βT^(n),where T is the scalar torsion andβand n are real con-stants.The acquired field equations incorporating the anisotropic matter source along with the quintessence field,in f(T)gravity,are investigated by making use of the specific character of the scalar torsion T for the observed stars PSRJ1614-2230,4U1608-52.CenX-3,EXO1785-248,and SMCX-1.It is suggested that all the stellar struc-tures under examination are advantageously independent of any central singularity and are stable.Comprehensive graphical analysis shows that various physical features which are crucially important for the emergence of the stellar structures are conferred.展开更多
Recent advances in nuclear theory and new astrophysical observations have led to the need for specific theoretical models applicable to dense-matter physics phenomena.Quantum chromodynamics(QCD)predicts the existence ...Recent advances in nuclear theory and new astrophysical observations have led to the need for specific theoretical models applicable to dense-matter physics phenomena.Quantum chromodynamics(QCD)predicts the existence of non-nucleonic degrees of freedom at high densities in neutron-star matter,such as quark matter.Within a confining quark matter model,which consists of homogeneous,neutral 3-flavor interacting quark matter with O(m_(s)^(4))corrections,we examine the structure of compact stars composed of a charged perfect fluid in the context of f(R,T)gravity.The system of differential equations describing the structure of charged compact stars has been derived and numerically solved for a gravity model with f(R,T)=R+2βT.For simplicity,we assumed that the charge density is proportional to the energy density,namely,ρ_(ch)=αρ.It is demonstrated that the matter-geometry coupling constant β and charge parameter α affect the total gravitational mass and the radius of the star.展开更多
In the last few decades,gravastars have been proposed as an alternative to black holes.The stability of a gravastar has been examined in many modified theories of gravity along with Einstein's GR.The f(Q,T)gravity...In the last few decades,gravastars have been proposed as an alternative to black holes.The stability of a gravastar has been examined in many modified theories of gravity along with Einstein's GR.The f(Q,T)gravity,a successfully modified theory of gravity for describing the current accelerated expansion of the universe,has been used in this study to examine gravastar in different aspects.According to Mazur and Mottola[Proc.Natl.Acad.Sci.101,9545(2004);Gravitational condensate stars:An alternative to black holes,I12-011,(2002)],a gravastar has three regions with three different equations of state.In this study,we examined the interior of a gravastar by consid-ering p=-ρ EoS to describe the dark sector for the interior region.The next region is a thin shell of ultrarelativistic stiff fluid,in which we investigated several physical properties,including proper length,energy,entropy,and surface energy density.Additionally,we examined the surface redshift and speed of sound to check the potential stability of our proposed thin-shell gravastar model.Furthermore,we used the entropy maximization technique to verify the stability of the gravastar model.A gravastar's outer region is a complete vacuum described by exterior Schwarzschild geometry.Finally,we presented a stable gravastar model,which is singularity-free and devoid of any incom-pleteness in classical black hole theory.展开更多
基金DST,New Delhi,India,for its financial support for research facilities under DSTFIST-2019。
文摘This paper investigates wormhole solutions within the framework of extended symmetric teleparallel gravity,incorporating non-commutative geometry,and conformal symmetries.To achieve this,we examine the linear wormhole model with anisotropic fluid under Gaussian and Lorentzian distributions.The primary objective is to derive wormhole solutions while considering the influence of the shape function on model parameters under Gaussian and Lorentzian distributions.The resulting shape function satisfies all the necessary conditions for a traversable wormhole.Furthermore,we analyze the characteristics of the energy conditions and provide a detailed graphical discussion of the matter contents via energy conditions.Additionally,we explore the effect of anisotropy under Gaussian and Lorentzian distributions.Finally,we present our conclusions based on the obtained results.
基金UGC for providing financial support in the form of the JRF fellowship via letter NTA Ref.No.:201610006334the financial support provided under the scheme‘Fund for Improvement of S&T Infrastructure(FIST)’of the Department of Science&Technology(DST),Government of India via letter No.SR/FST/MS-I/2021/104 to the Department of Mathematics and Statistics,Central University of Punjab。
文摘In this paper,the non-static solutions for perfect fluid distribution with plane symmetry in f(R,T)gravitational theory are obtained.Firstly,using the Lie symmetries,symmetry reductions are performed for considered vector fields to reduce the number of independent variables.Then,corresponding to each reduction,exact solutions are obtained.Killing vectors lead to different conserved quantities.Therefore,we figure out the Killing vector fields corresponding to all derived solutions.The derived solutions are further studied and it is observed that all of the obtained spacetimes,at least admit to the minimal symmetry group which consists of δ_(y),δ_(z) and -zδ_(y)+yδ_(z).The obtained metrics,admit to 3,4,6,and 10,Killing vector fields.Conservation of linear momentum in the direction of y and z,and angular momentum along the x axis is provided by all derived solutions.
基金funded by the National Natural Science Foundation of China (Grant No. 11975145)
文摘This study aims to discuss anisotropic solutions that are spherically symmetric in the quintessence field,which describe compact stellar objects in the modified Rastall teleparallel theory of gravity.To achieve this goal,the Krori and Barua arrangement for spherically symmetric components of the line element is incorporated.We explore the field equations by selecting appropriate off-diagonal tetrad fields.Born-Infeld function of torsion f(T)=β√λT+1-1 and power law form h(T)=δTn are used.The Born-Infeld gravity was the first modified teleparallel gravity to discuss inflation.We use the linear equation of state pr=ξρto separate the quintessence density.After obtaining the field equations,we investigate different physical parameters that demonstrate the stability and physical acceptability of the stellar models.We use observational data,such as the mass and radius of the compact star candidates PSRJ 1416-2230,Cen X-3,&4U 1820-30,to ensure the physical plausibility of our findings.
基金National Research Foundation(NRF)of South Africa for the postdoctoral fellowship award。
文摘To obtain analytically relativistic quintessence anisotropic spherical solutions in the f(T)paradigm is the primary objective of this paper.To do this,the pressure anisotropy condition is imposed,and we employ a metric potential of the Tolman–Kuchowicz(TK)type.We also suppose that our current model incorporates a quintessence field characterized by a parameterωq,in addition to the anisotropic matter distribution.In the presence of the parameterα,the field equations are modified by the choice of the f(T)function.The f(T)gravity parameterαadds new components to the basic physical characteristics,such as density,pressure,subliminal sound velocity,surface redshift,etc,of the present model.By selecting the compact star Her X-1 and varyingαfrom 0.5 to 2.5,we examined all the physical characteristics of the model parameter of the configuration.The graphical process demonstrates that a more compact item is produced with greater values ofα.The hydrostatic equilibrium condition of the model is discussed,as well as the mass-radius relationship for our current model is obtained.
文摘In this paper,we classify static spherically symmetric(SS)perfect fluid space-times via conformal vector fields(CVFs)in f(T)gravity.For this analysis,we first explore static SS solutions by solving the Einstein field equations in f(T)gravity.Secondly,we implement a direct integration technique to classify the resulting solutions.During the classification,there arose 20 cases.Studying each case thoroughly,we came to know that in three cases the space-times under consideration admit proper CVFs in f(T)gravity.In one case,the space-time admits proper homothetic vector fields,whereas in the remaining 16 cases either the space-times become conformally flat or they admit Killing vector fields.
文摘In this paper,we study a theory of gravity called mimetic f(R,T)in the presence of swampland dS conjecture.For this purpose,we introduce several inflation solutions of the Hubble parameter H(N)from f(R,T)=R+δT gravity model,in which R is Ricci scalar,and T denotes the trace of the energy–momentum tensor.Also,δand N are the free parameter and a number of e-fold,respectively.Then we calculate quantities such as potential,Lagrange multiplier,slow-roll,and some cosmological parameters such as nsand r.Then we challenge the mentioned inflationary model from the swampland dS conjecture.We discuss the stability of the model and investigate the compatibility or incompatibility of this inflationary scenario with the latest Planck observable data.
基金the Science Committee of the Ministry of Education and Science of the Republic of Kazakhstan provided funding for this study(Grant No.AP09058240)。
文摘Some recent developments(accelerated expansion)in the Universe cannot be explained by the conventional formulation of general relativity.We apply the recently proposed f(T,B)gravity to investigate the accelerated expansion of the Universe.By parametrizing the Hubble parameter and estimating the best fit values of the model parameters b_(0),b_(1),and b_(2)imposed from Supernovae type la,Cosmic Microwave Background,B aryon Acoustic Oscillation,and Hubble data using the Markov Chain Monte Carlo method,we propose a method to determine the precise solutions to the field equations.We then observe that the model appears to be in good agreement with the observations.A change from the deceleration to the acceleration phase of the Universe is shown by the evolution of the deceleration parameter.In addition,we investigate the behavior of the statefinder analysis,equation of state(EoS)parameters,along with the energy conditions.Furthermore,to discuss other cosmological parameters,we consider some wellknown f(T,B)gravity models,specifically,f(T,B)=aT^(b)+cB^(d).Lastly,we find that the considered f(T,B)gravity models predict that the present Universe is accelerating and the EoS parameter behaves like the ACDM model.
文摘We report a viable exponential gravity model for the accelerated expansion of the universe in Bianchi VI<sub>h</sub> space-time. By considering the estimated physical parameters, the cosmological models are constructed and analyzed in detail. We found that the state parameter in both the models increases to a higher negative range in an early epoch of the phantom domain and it goes to the positive domain at a late phase of the evolution. The effective cosmological constant remains in a positive domain for both models, which is a good sign of accelerating expansion of the universe.
基金support from the administration of the University of Nizwasupport of COST Actions CA21106 and CA22113TUBITAK,SCOAP3,and ANKOS for their support.
文摘This study explores the f(R,T)gravity theory,which introduces a coupling between matter and curvature,through the simplest linear functional form f(R,T)=R+2βT.We derive the modified Einstein field equations and conservation equations for this theory and then apply this framework to study the structural properties of quark stars(QSs)composed of interacting quark matter,considering perturbative QCD corrections and color superconductivity.By solving the modified Tolman-Oppenheimer-Volkoff equations,we investigate the mass-radius relation,stability criteria,and energy conditions of QSs.Our results indicate that the f(R,T)gravity significantly influences the properties of QSs,leading to deviations from General Relativity.The analysis is consistent with recent observational data,suggesting that the modified gravity framework could provide viable models for the study of compact stars.
基金Supported by Walailak University under the New Researcher Development scheme(WU67268)A.Pradhan expresses gratitude to the IUCCA in Pune,India,for offering facilities under associateship programs.In addition,İzzet Sakallıthanks TÜBİTAK,ANKOS,and SCOAP3 for their contributions.Takol Tangphati andİzzet Sakallıalso appreciate COST Actions CA21106 and CA22113 for their networking support。
文摘We investigated the impact of f(R,L_(m),T)gravity on the internal structure of compact stars,expecting this theory to manifest prominently in the high-density cores of such stars.We considered the algebraic function,f(R,L_(m),T)=R+αTL_(m),whereαrepresents the matter-geometry coupling constant.We specifically chose the matter Lagrangian density L_(m)=-ρto explore compact stars with anisotropic pressure.To this end,we employed the MIT bag model as an equation of state.Subsequently,we numerically solved the hydrostatic equilibrium equations to obtain mass-radius relations for quark stars(QSs),examining static stability criteria,adiabatic index,and speed of sound.Finally,we used recent astrophysical data to constrain the coupling parameterα,which may lead to either larger or smaller masses for QSs,compared to their counterparts in general relativity.
基金Supported by the“PhD-Associate Scholarship–PASS”grant(number 29 UMP2023)of the National Center for Scientific and Technical Research in Morocco。
文摘In this paper,we use genetic algorithms,a specific machine learning technique,to achieve a model-independent reconstruction of f(T)gravity.By using H(z)data derived from cosmic chronometers and the radial Baryon Acoustic Oscillation method,including the latest Dark Energy Spectroscopic Instrument(DESI)data,we reconstruct the Hubble rate,which is the basis parameter for reconstructing f(T)gravity without any assumptions.In this reconstruction process,we use the current value of the Hubble rate,H_(0),derived by genetic algorithms.The reconstructed f(T)function is consistent with the standardΛCDM cosmology within the 1 confidence level across a broad temporal range.The mean f(T)curve,adopting a quadratic form,prompts us to parametrize it using a second-degree polynomial.This quadratic deviation from theΛCDM scenario is mildly favored by the data.
文摘In this paper,we investigate the topological charge and conditions for the existence of the photon sphere in Kiselev-anti-de Sitter(AdS)black holes within f(R,T)gravity.Furthermore,we establish their topological classifications.We employ two different methods based on Duan's topological current p-mapping theory viz analysis of temperature and the generalized Helmholtz free energy methods to study the topological classes of our black hole.Considering this black hole,we discuss the critical and zero points(topological charges and topological numbers)for different parameters.Our findings reveal that the Kiselev parameter o and f(R,T)gravity parameter y influence the number of topological charges of black holes,providing novel insights into topological classifications.We observe that for given values of the free parameters,total topological charges(Q_(total)=-1)exist for the T method and total topological numbers(ω=+1)for the generalized Helmholtz free energy method.Our research findings elucidate that,in contrast to the scenario in whichω=1/3,in other cases,increasing y increases the number of total topological charges for the black hole.Interestingly,for the phantom field(ω=-4/3),we observe that decreasingγincreases the number of topological charges.Additionally,we study the results for the photon sphere.The studied models reveal that the simultaneous presence ofγandωeffectively expands the permissible range forγ.In other words,the model can exhibit black hole behavior over a larger domain.Additionally,we observe that with the stepwise reduction ofγ,the region covered by singularity diminishes and becomes more restricted.However,an interesting point about all three ranges is the elimination of the forbidden region in this model.In other words,this model and the investigated areas appear to have no region in which both theφand metric functions simultaneously lack solutions.Additionally,we fully check the curvatures singularities and energy conditions for the mentioned black hole.
基金B.H.would like to thank DST-INSPIRE,Ministry of Science and Technology fellowship program,Govt.of India for awarding the DST/INSPIRE Fellowship(IF220255)for financial support.
文摘We explored two f(R,T)gravity models and derived black hole solutions within these models.We focus on investigating how the f(R,T)model influences the thermodynamic characteristics of black holes by studying their thermodynamic topology and thermodynamic geometry.We consid-ered five specific values of the thermodynamic parameter w,which signify five different classes of black hole solutions in general relativity(GR).We observed significant changes in the local topological properties of these black holes compared to GR,depending on the model parameters.Notably,we identified an additional topological class W=O for some values of w that is absent in the GR framework.We also studied the ther-modynamic geometry of the black hole using the Geometrothermodynam-ics(GTD)formalism.Our analysis demonstrates that the singular point,where the GTD scalar curvature diverges,corresponds exactly to the point where the heat capacity changes sign.Additionally,we constrained the model parameters of both models considered by utilizing black hole shadow data from the Sgr A*black hole,measured by the Event Horizon Telescope(EHT).
文摘This paper presents a picture of compact structures for the f(R,T)model of the form R+γe^χT,withγandχbeing parameters.The poly tropic equation of state and the MIT bag model reflect the pressure density relation for these compact objects.For this purpose,a system of two differential equations involving pressure as well as the mass of the stellar structure is obtained from field equations and the Tolman-Oppenheimer-Volkoff(TOV)equation.The numerical solution of this system gives a graphical description of various characteristics of these compact systems.To examine the viability and stability of assumed configurations,the energy conditions,causality relation and adiabatic index are discussed for the presumed scenario.
基金Sudan Hansraj is grateful to the National Research Foundation of South Africa for support through Grant 138012the National Research Foundation of South Africa for the award of a postdoctoral fellowship。
文摘Dark energy is typically the principal component needed for the traversability of wormholes(WH),as it provides the negative gravity effect required to keep the throat open.However,can this be achieved without dark energy?It turns out that if we couple the trace of energy-momentum with the standard Einstein-Hilbert Lagrangian and utilize a specific equation of state(EoS),dark energy may be obviated.The Casimir stress energy is known to result in the violation of the null energy condition(NEC)on the energy momentum tensor.This phenomenon makes such an EoS an ideal candidate for generating traversable WH geometries.The laboratory proven phenomenon provides a natural mechanism to sustain an open WH throat without relying on dark energy.Therefore,we generate two classes of WH solutions using this in energy-momentum trace-coupling gravity.For the specific choice of the Casimir EoS relating the energy-momentum tensor components[Kar and Sahdev:Phys.Rev.D 52,2030(1995)]and different choices of redshift functions,we determine the WH geometry completely.The obtained WH solutions violate the NECs,and all qualitative constraints demanded for physically realizable WHs are satisfied.This is demonstrated via graphical plots for a suitably chosen range of coupling parameter values.Furthermore,our study investigates the repulsive effect of gravity,revealing that its presence leads to a negative deflection angle for photons traveling along null geodesics.Notably,we observe a consistent pattern of negative values for the deflection angle across all values of r_(0) in the three scenarios considered,thus indicating the clear manifestation of the repulsive gravity effect.All of this is possible without invoking the existence of dark energy.
基金supported by the University Grants Commission(UGC),New Delhi,India,for awarding National Fellowship for Scheduled Caste Students(UGC-Ref.No.201610123801)supported by the Council of Scientific and Industrial Research(CSIR),Government of India,New Delhi,for junior research fellowship(File No.09/1026(13105)/2022-EMR-I)supported by the National Board for Higher Mathematics(NBHM)under the Department of Atomic Energy(DAE),Govt.of India for financial support to carry out the research project(No.02011/3/2022 NBHM(R.P.)/R&D II/2152 Dt.14.02.2022)
文摘In this study,we conduct an analysis of traversable wormhole solutions within the framework of linear f(Q,T)=αQ+βT gravity,ensuring that all energy conditions hold for the entire spacetime.The solutions presented in this paper are derived through a comprehensive analytical examination of the parameter space associated with the wormhole model.This involves considering the exponents governing the redshift and shape functions,as well as the radius of the wormhole throat(r_(0)),the redshift function value at the throat(∅_(0)),and the model parameters(αandβ).Moreover,we establish bounds on these free parameters,which guarantee the satisfaction of the energy conditions throughout spacetime and also provide two solutions.Furthermore,we use the Israel junction condition to observe the stability of a thin-shell around the wormhole.Finally,we calculate the null energy condition criteria as well as the potential for the thin-shell and how it varies with the chosen shape function.
基金University Grants Commission(UGC),New Delhi,India,for awarding National Fellowship for Scheduled Caste Students(UGC-Ref.No.:201610123801)the Department of Science and Technology(DST),Government of India,New Delhi,for awarding a Senior Research Fellowship(File No.DST/INSPIRE Fellowship/2019/IF190911)National Board for Higher Mathematics(NBHM)under Department of Atomic Energy(DAE),Govt.of India for financial support to carry out the Research project No.:02011/3/2022 NBHM(R.P.)/R&D II/2152 Dt.14.02.2022。
文摘In this study,we obtain wormhole solutions in the recently proposed extension of symmetric teleparallel gravity,known as f(Q,T)gravity.Here,the gravitational Lagrangian L is defined by an arbitrary function f of Q and T,where Q is a non-metricity scalar,and T is the trace of the energy-momentum tensor.In this study,we obtain field equations for a static spherically symmetric wormhole metric in the context of general f(Q,T)gravity.We study the wormhole solutions using(ⅰ)a linear equation of state and(ⅱ)an anisotropy relation.We adopt two different forms of f(Q,T),(a)linear f(Q,T)=αQ+βT and(b)non-linear f(Q,T)=Q+λQ^(2)+ηT,to investigate these solutions.We investigate various energy conditions to search for preservation and violation among the obtained solutions and find that the null energy condition is violated in both cases of our assumed forms of f(Q,T).Finally,we perform a stability analysis using the Tolman-Oppenheimer-Volkov equation.
文摘This work suggests a new model for anisotropic compact stars with quintessence in f(T)gravity by us-ing the off-diagonal tetrad and the power-law as f(T)=βT^(n),where T is the scalar torsion andβand n are real con-stants.The acquired field equations incorporating the anisotropic matter source along with the quintessence field,in f(T)gravity,are investigated by making use of the specific character of the scalar torsion T for the observed stars PSRJ1614-2230,4U1608-52.CenX-3,EXO1785-248,and SMCX-1.It is suggested that all the stellar struc-tures under examination are advantageously independent of any central singularity and are stable.Comprehensive graphical analysis shows that various physical features which are crucially important for the emergence of the stellar structures are conferred.
基金financial support from the PCI program of the Brazilian agency"Conselho Nacional de Desenvolvimento Científico e Tecnológico"-CNPqsupported by King Mongkut's University of Technology Thonburi's Post-doctoral Fellowship。
文摘Recent advances in nuclear theory and new astrophysical observations have led to the need for specific theoretical models applicable to dense-matter physics phenomena.Quantum chromodynamics(QCD)predicts the existence of non-nucleonic degrees of freedom at high densities in neutron-star matter,such as quark matter.Within a confining quark matter model,which consists of homogeneous,neutral 3-flavor interacting quark matter with O(m_(s)^(4))corrections,we examine the structure of compact stars composed of a charged perfect fluid in the context of f(R,T)gravity.The system of differential equations describing the structure of charged compact stars has been derived and numerically solved for a gravity model with f(R,T)=R+2βT.For simplicity,we assumed that the charge density is proportional to the energy density,namely,ρ_(ch)=αρ.It is demonstrated that the matter-geometry coupling constant β and charge parameter α affect the total gravitational mass and the radius of the star.
基金SP&PKS acknowledges the National Board for Higher Mathematics(NBHM)under the Department of Atomic Energy(DAE),Govt.of India for financial support to carry out the Research project No.:02011/3/2022 NBHM(R.P.)/R&D II/2152 Dt.14.02.2022.PKS thanks Transilvania University of Brasov for Transilvania Fellowship for Visiting Professors。
文摘In the last few decades,gravastars have been proposed as an alternative to black holes.The stability of a gravastar has been examined in many modified theories of gravity along with Einstein's GR.The f(Q,T)gravity,a successfully modified theory of gravity for describing the current accelerated expansion of the universe,has been used in this study to examine gravastar in different aspects.According to Mazur and Mottola[Proc.Natl.Acad.Sci.101,9545(2004);Gravitational condensate stars:An alternative to black holes,I12-011,(2002)],a gravastar has three regions with three different equations of state.In this study,we examined the interior of a gravastar by consid-ering p=-ρ EoS to describe the dark sector for the interior region.The next region is a thin shell of ultrarelativistic stiff fluid,in which we investigated several physical properties,including proper length,energy,entropy,and surface energy density.Additionally,we examined the surface redshift and speed of sound to check the potential stability of our proposed thin-shell gravastar model.Furthermore,we used the entropy maximization technique to verify the stability of the gravastar model.A gravastar's outer region is a complete vacuum described by exterior Schwarzschild geometry.Finally,we presented a stable gravastar model,which is singularity-free and devoid of any incom-pleteness in classical black hole theory.
