This paper explores the dynamical feature of Hayward-Letelier black holes in AdS spacetime,emphasizing the effects of the Hayward parameter g,mass M,cosmological constant L,and modification parameterαon their geometr...This paper explores the dynamical feature of Hayward-Letelier black holes in AdS spacetime,emphasizing the effects of the Hayward parameter g,mass M,cosmological constant L,and modification parameterαon their geometry,thermodynamics,and observational features.By utilizing an effective potential method,we investigate the paths of particles,innermost stable circular orbit,and behavior of photon spheres,which connects them to the appearance of black hole shadows.Thermodynamic features such as Hawking temperature and entropy are studied for investigating the effect of L and thermal fluctuations on the stability of black holes.These discoveries connect theoretical ideas with observational astrophysics,which enhances our comprehension of ordinary black holes in AdS models.In this study,we analytically compute the greybody factor for a massless scalar field propagating in the vicinity of a black hole under the assumption of weak coupling to gravity.We investigate the behavior of the effective potential concerning the black hole's mass and charge,revealing that it reaches its maximum at lower values of the cloud of strings parameter.Our results indicate that the radial absorption rate of the scalar field exhibits significant fluctuations,which is influenced by the charge of the black hole and clouds of string,with implications for the dynamics of scalar fields in strong gravitational fields.展开更多
In this study,we used the gravitational decoupling method(GD)via minimal geometric deformation(MGD)to analyze strange deformed stars(SS)within the modified f(T)gravity theory.By adopting the Buchdahl ansatz and the qu...In this study,we used the gravitational decoupling method(GD)via minimal geometric deformation(MGD)to analyze strange deformed stars(SS)within the modified f(T)gravity theory.By adopting the Buchdahl ansatz and the quadratic polytropic equation of state(EOS),we derived deformed SS models by assuming that the energy-momentum components of the deformed fluid satisfyρ=Θ_(0)^(0) and p_(r)=Θ_(1)^(1).This app_(r)oach leads to different classes of exact solutions.The study of physical viability tests ensures that the p_(r)oposed configurations adhere to realistic constraints.Furthermore,we analyzed the impact of relevant parameters in three scenarios:GR,f(T),and f(T)+MGD.In addition,observational constraints were used for comparison with GW190814 and neutron stars(NSTRs)PSR J1614-2230 and PSR J1903+327,with mass ranges of 2.5-2.67M_(⊙),1.97±0.04M_(⊙),and1.667±0.021M_(⊙),respectively.Remarkably,we observed from the M-Rcurves that NSTRs with masses ranging from 2.4 to 3.5M_(⊙)correspond to a range of radii from 9.08_(-0.01)^(+0.02)to 13.01_(-0.01)^(+0.01)km for different values of the parametersα,β,γ,andζ_(1).Notably,for theρ=Θ_(0)^(0)solution,higher values ofαp_(r)oduce NSTRs with smaller masses and radii,while the p_(r)=Θ_(1)^(1)solution yields larger masses and radii.This evidences the existence of massive NSTRs within the modified gravity theory f(T).展开更多
This study examines a recently hypothesized black hole,which is a perfect solution of metric-affine gravity with a positive cosmological constant,and its thermodynamic features as well as the Joule-Thomson expansion.W...This study examines a recently hypothesized black hole,which is a perfect solution of metric-affine gravity with a positive cosmological constant,and its thermodynamic features as well as the Joule-Thomson expansion.We develop some thermodynamical quantities,such as volume,Gibbs free energy,and heat capacity,using the entropy and Hawking temperature.We also examine the first law of thermodynamics and thermal fluctuations,which might eliminate certain black hole instabilities.In this regard,a phase transition from unstable to stable is conceivable when the first law order corrections are present.In addition,we study the efficiency of this system as a heat engine and the effect of metric-affine gravity for the physical parameters q_(e),q_(m),κ_(s),κ_(d),and κ_(sh).Further,we study the Joule-Thomson coefficient and inversion temperature,and observe the isenthalpic curves in the Ti−Pi plane.In metric-affine gravity,a comparison is made between a van der Waals fluid and a black hole to study their similarities and differences.展开更多
We conduct an investigation to explore late-time cosmic acceleration through various dark energy parametrizations(Wettrich,Efstathiou,and Ma-Zhang)within the Horava-Lifshitz gravity framework.As an alternative to gene...We conduct an investigation to explore late-time cosmic acceleration through various dark energy parametrizations(Wettrich,Efstathiou,and Ma-Zhang)within the Horava-Lifshitz gravity framework.As an alternative to general relativity,this theory introduces anisotropic scaling at ultraviolet scales.Our primary objective is to constrain the key cosmic parameters and baryon acoustic oscillation(BAO)scale,specifically the sound horizon(rd),by utilizing 24 uncorrelated measurements of BAOs derived from recent galaxy surveys spanning a redshift range from z=0.106 to z=2.33.Additionally,we integrate the most recent Hubble constant measurement by Riess in 2022(denoted as R22)as an extra prior.For the parametrizations of Wettrich,Efstathiou,and Ma-Zhang,our analysis of BAO data yields sound horizon results of r_(d)=148.1560±2.7688 Mpc,r_(d)=148.6168±10.2469 Mpc,and r_(d)=147.9737±10.6096 Mpc,respectively.Incorporating the R22 prior into the BAO dataset results in r_(d)=139.5806±3.8522 Mpc,r_(d)=139.728025±2.7858 Mpc,and r_(d)=139.6001±2.7441 Mpc.These outcomes highlight a distinct inconsistency between early and late observational measurements,analogous to the H_(0) tension.A notable observation is that,when we do not include the R22 prior,the outcomes for rd tend to be in agreement with Planck and SDSS results.Following this,we conducted a cosmography test and comparative study of each parametrization within the Lambda Cold Dark Matter paradigm.Our diagnostic analyses demonstrate that all models fit seamlessly within the phantom region.All dark energy parametrizations predict an equation of state parameter close ω=-1,indicating a behavior similar to that of a cosmological constant.The statistical analysis indicates that neither of the two models can be ruled out based on the latest observational measurements.展开更多
In this study,we observe that,in the presence of the string cloud parameter a and the quintessence parameterγ,with the equation of state parameter,ω_(q) = -2/3the radius of the shadow of the Schwarzschild black hole...In this study,we observe that,in the presence of the string cloud parameter a and the quintessence parameterγ,with the equation of state parameter,ω_(q) = -2/3the radius of the shadow of the Schwarzschild black hole increases as compared with that in the pure Schwarzschild black hole case.The existence of both quintessential dark energy and the cloud of strings increases the shadow size;hence,the strength of the gravitational field around the Schwarzschild black hole increases.Using the data collected by the Event Horizon Telescope(EHT)collaboration for M87*and Sgr A*,we obtain upper bounds on the values of a andγ.Further,we see the effects of a andγon the rate of emission energy for the Schwarzschild black hole.We notice that the rate of emission energy is higher in the presence of clouds of strings and quintessence.Moreover,we study the weak deflection angle using the Gauss-Bonnet theorem.We show the influence of a andγon the weak deflection angle.We notice that both a andγincrease the deflection angleα.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
The main aim of this study is to explore the existence and salient features of spherically symmetric relativistic quark stars in the background of massive Brans-Dicke gravity.The exact solutions to the modified Einste...The main aim of this study is to explore the existence and salient features of spherically symmetric relativistic quark stars in the background of massive Brans-Dicke gravity.The exact solutions to the modified Einstein field equations are derived for specific forms of coupling and scalar field functions using the equation of state relating to the strange quark matter that stimulates the phenomenological MIT-Bag model as a free Fermi gas of quarks.We use a well-behaved function along with the Karmarkar condition for class-one embedding as well as junction conditions to determine the unknown metric tensors.The radii of strange compact stars viz.,PSR J1416-2230,PSR J1903+327,4U 1820-30,CenX-3,and EXO1785-248,are predicted via their observed mass for different values of the massive Brans-Dicke parameters.We explore the influences of the mass of scalar field m_(ϕ),coupling parameter ωBD,and bag constant B on state determinants and perform several tests on the viability and stability of the constructed stellar model.Conclusively,we find that our stellar system is physically viable and stable as it satisfies all the energy conditions and necessary stability criteria under the influence of a gravitational scalar field.展开更多
基金Supported by the Ongoing Research Funding Program,(ORF-2025-650),King Saud University,Riyadh,Saudi Arabia.
文摘This paper explores the dynamical feature of Hayward-Letelier black holes in AdS spacetime,emphasizing the effects of the Hayward parameter g,mass M,cosmological constant L,and modification parameterαon their geometry,thermodynamics,and observational features.By utilizing an effective potential method,we investigate the paths of particles,innermost stable circular orbit,and behavior of photon spheres,which connects them to the appearance of black hole shadows.Thermodynamic features such as Hawking temperature and entropy are studied for investigating the effect of L and thermal fluctuations on the stability of black holes.These discoveries connect theoretical ideas with observational astrophysics,which enhances our comprehension of ordinary black holes in AdS models.In this study,we analytically compute the greybody factor for a massless scalar field propagating in the vicinity of a black hole under the assumption of weak coupling to gravity.We investigate the behavior of the effective potential concerning the black hole's mass and charge,revealing that it reaches its maximum at lower values of the cloud of strings parameter.Our results indicate that the radial absorption rate of the scalar field exhibits significant fluctuations,which is influenced by the charge of the black hole and clouds of string,with implications for the dynamics of scalar fields in strong gravitational fields.
基金Government of India for providing financial assistance to conduct the Research project No.:02011/3/2022 NBHM(R.P)/R&D II/2152 Dt.14.02.2022National Research Foundation of South Africa for awarding a postdoctoral fellowship。
文摘In this study,we used the gravitational decoupling method(GD)via minimal geometric deformation(MGD)to analyze strange deformed stars(SS)within the modified f(T)gravity theory.By adopting the Buchdahl ansatz and the quadratic polytropic equation of state(EOS),we derived deformed SS models by assuming that the energy-momentum components of the deformed fluid satisfyρ=Θ_(0)^(0) and p_(r)=Θ_(1)^(1).This app_(r)oach leads to different classes of exact solutions.The study of physical viability tests ensures that the p_(r)oposed configurations adhere to realistic constraints.Furthermore,we analyzed the impact of relevant parameters in three scenarios:GR,f(T),and f(T)+MGD.In addition,observational constraints were used for comparison with GW190814 and neutron stars(NSTRs)PSR J1614-2230 and PSR J1903+327,with mass ranges of 2.5-2.67M_(⊙),1.97±0.04M_(⊙),and1.667±0.021M_(⊙),respectively.Remarkably,we observed from the M-Rcurves that NSTRs with masses ranging from 2.4 to 3.5M_(⊙)correspond to a range of radii from 9.08_(-0.01)^(+0.02)to 13.01_(-0.01)^(+0.01)km for different values of the parametersα,β,γ,andζ_(1).Notably,for theρ=Θ_(0)^(0)solution,higher values ofαp_(r)oduce NSTRs with smaller masses and radii,while the p_(r)=Θ_(1)^(1)solution yields larger masses and radii.This evidences the existence of massive NSTRs within the modified gravity theory f(T).
基金Supported by the Natural Sciences Foundation of China(11975145)Faisal Javed acknowledges(YS304023917)the Support to his Postdoctoral Fellowship at Zhejiang Normal University,ChinaG.Mustafa acknowledges Grant No.ZC304022919 to Support his Postdoctoral Fellowship at Zhejiang Normal University,China。
文摘This study examines a recently hypothesized black hole,which is a perfect solution of metric-affine gravity with a positive cosmological constant,and its thermodynamic features as well as the Joule-Thomson expansion.We develop some thermodynamical quantities,such as volume,Gibbs free energy,and heat capacity,using the entropy and Hawking temperature.We also examine the first law of thermodynamics and thermal fluctuations,which might eliminate certain black hole instabilities.In this regard,a phase transition from unstable to stable is conceivable when the first law order corrections are present.In addition,we study the efficiency of this system as a heat engine and the effect of metric-affine gravity for the physical parameters q_(e),q_(m),κ_(s),κ_(d),and κ_(sh).Further,we study the Joule-Thomson coefficient and inversion temperature,and observe the isenthalpic curves in the Ti−Pi plane.In metric-affine gravity,a comparison is made between a van der Waals fluid and a black hole to study their similarities and differences.
文摘We conduct an investigation to explore late-time cosmic acceleration through various dark energy parametrizations(Wettrich,Efstathiou,and Ma-Zhang)within the Horava-Lifshitz gravity framework.As an alternative to general relativity,this theory introduces anisotropic scaling at ultraviolet scales.Our primary objective is to constrain the key cosmic parameters and baryon acoustic oscillation(BAO)scale,specifically the sound horizon(rd),by utilizing 24 uncorrelated measurements of BAOs derived from recent galaxy surveys spanning a redshift range from z=0.106 to z=2.33.Additionally,we integrate the most recent Hubble constant measurement by Riess in 2022(denoted as R22)as an extra prior.For the parametrizations of Wettrich,Efstathiou,and Ma-Zhang,our analysis of BAO data yields sound horizon results of r_(d)=148.1560±2.7688 Mpc,r_(d)=148.6168±10.2469 Mpc,and r_(d)=147.9737±10.6096 Mpc,respectively.Incorporating the R22 prior into the BAO dataset results in r_(d)=139.5806±3.8522 Mpc,r_(d)=139.728025±2.7858 Mpc,and r_(d)=139.6001±2.7441 Mpc.These outcomes highlight a distinct inconsistency between early and late observational measurements,analogous to the H_(0) tension.A notable observation is that,when we do not include the R22 prior,the outcomes for rd tend to be in agreement with Planck and SDSS results.Following this,we conducted a cosmography test and comparative study of each parametrization within the Lambda Cold Dark Matter paradigm.Our diagnostic analyses demonstrate that all models fit seamlessly within the phantom region.All dark energy parametrizations predict an equation of state parameter close ω=-1,indicating a behavior similar to that of a cosmological constant.The statistical analysis indicates that neither of the two models can be ruled out based on the latest observational measurements.
基金the Grant No.ZC304022919 to support his Postdoctoral Fellowship at Zhejiang Normal Universitythe support of Inha University in Tashkent and research work has been supported by the Visitor Research Fellowship at Zhejiang Normal Universitysupported by Research Grant FZ-20200929344,F-FA-2021-510 and F-FA-2021-432 of the Uzbekistan Ministry for Innovative Development。
文摘In this study,we observe that,in the presence of the string cloud parameter a and the quintessence parameterγ,with the equation of state parameter,ω_(q) = -2/3the radius of the shadow of the Schwarzschild black hole increases as compared with that in the pure Schwarzschild black hole case.The existence of both quintessential dark energy and the cloud of strings increases the shadow size;hence,the strength of the gravitational field around the Schwarzschild black hole increases.Using the data collected by the Event Horizon Telescope(EHT)collaboration for M87*and Sgr A*,we obtain upper bounds on the values of a andγ.Further,we see the effects of a andγon the rate of emission energy for the Schwarzschild black hole.We notice that the rate of emission energy is higher in the presence of clouds of strings and quintessence.Moreover,we study the weak deflection angle using the Gauss-Bonnet theorem.We show the influence of a andγon the weak deflection angle.We notice that both a andγincrease the deflection angleα.
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Supported by the Postdoctoral Fellowship at Zhejiang Normal University(ZC304022919)。
文摘The main aim of this study is to explore the existence and salient features of spherically symmetric relativistic quark stars in the background of massive Brans-Dicke gravity.The exact solutions to the modified Einstein field equations are derived for specific forms of coupling and scalar field functions using the equation of state relating to the strange quark matter that stimulates the phenomenological MIT-Bag model as a free Fermi gas of quarks.We use a well-behaved function along with the Karmarkar condition for class-one embedding as well as junction conditions to determine the unknown metric tensors.The radii of strange compact stars viz.,PSR J1416-2230,PSR J1903+327,4U 1820-30,CenX-3,and EXO1785-248,are predicted via their observed mass for different values of the massive Brans-Dicke parameters.We explore the influences of the mass of scalar field m_(ϕ),coupling parameter ωBD,and bag constant B on state determinants and perform several tests on the viability and stability of the constructed stellar model.Conclusively,we find that our stellar system is physically viable and stable as it satisfies all the energy conditions and necessary stability criteria under the influence of a gravitational scalar field.
