Ertan GÜDEKLİ - Academia.edu (original) (raw)
Papers by Ertan GÜDEKLİ
In a recent work, it has been proposed that the recent cosmic passage to a cosmic acceleration er... more In a recent work, it has been proposed that the recent cosmic passage to a cosmic acceleration era is the result of the existence of small anti-gravity sources in each galaxy and clusters of galaxies. In particular, a swiss-cheese cosmology model which relativistically integrates the contribution of all these anti-gravity sources on galactic scale has been constructed assuming the presence of an infrared fixed point for a scale dependent cosmological constant. The derived cosmological expansion provides explanation for both the fine tuning and the coincidence problem. The present work relaxes the previous assumption on the running of the cosmological constant and allows for a generic scaling around the infrared fixed point. Our analysis reveals in order to produce a cosmic evolution consistent with the best ΛCDM model, the IR-running of the cosmological constant is consistent with the presence of an IR-fixed point.
In this paper, we investigate f(T) cosmology and find an exact solution for f which gives a Littl... more In this paper, we investigate f(T) cosmology and find an exact solution for f which gives a Little Rip cosmology. Also, considering accelerating cosmology with dark matter, the time-dependent solution is found. For these cases, by using solutions obtained from f(T) gravity we find expressions for ω and Λ defined as time functions via equivalent description in terms of inhomogeneous fluid. This puts the question: which theoretical model describes the observational cosmology?
In this paper we consider the equation of motion for<br> the F (R, T) gravity on their prop... more In this paper we consider the equation of motion for<br> the F (R, T) gravity on their property of conformal invariance. It<br> is shown that in the general case, such a theory is not conformal<br> invariant. Studied special cases for the functions v and u in which<br> can appear properties of the theory. Also we consider cosmological<br> aspects F (R, T) theory of gravity, having considered particular case<br> F (R, T) = μR+νT^2. Showed that in this case there is a nonlinear<br> dependence of the parameter equation of state from time to time,<br> which affects its evolution.
In this letter, we explore exact solutions for the<br> Horava-Lifshitz gravity. We use of a... more In this letter, we explore exact solutions for the<br> Horava-Lifshitz gravity. We use of an extension of this theory with<br> first order dynamical lapse function. The equations of motion have<br> been derived in a fully consistent scenario. We assume that there<br> are some spherically symmetric families of exact solutions of this<br> extended theory of gravity. We obtain exact solutions and investigate<br> the singularity structures of these solutions. Specially, an exact<br> solution with the regular horizon is found.
Research in Astronomy and Astrophysics, 2021
The work reported in this paper demonstrates the cosmology of f(Q) gravity and the reconstruction... more The work reported in this paper demonstrates the cosmology of f(Q) gravity and the reconstruction of various associated parameters with different versions of holographic dark energy with generalized cut-offs, where Q = 6 H 2. The Universe is considered to be filled with viscous fluid characterized by a viscous pressure Π = – 3 H ξ, where ξ = ξ 0 + ξ 1 H + ξ 2 ( H ˙ + H 2 ) and H is the Hubble parameter. Considering the power law form of expansion, we have derived the expression of f(Q) under a non-viscous holographic framework and it is then extended to viscous cosmological settings with extended generalized holographic Ricci dark energy. The forms of f(Q) for both the cases are found to be monotonically increasing functions of Q. In the viscous holographic framework, f(Q) is reconstructed as a function of cosmic time t and is found to stay at a positive level with Nojiri-Odintsov cut-off. In these cosmological settings, the slow roll parameters are computed and a scope of exit from...
Symmetry, 2021
A scheme for the generalized Chaplygin gas equation of state is shown by using the holographic Ri... more A scheme for the generalized Chaplygin gas equation of state is shown by using the holographic Ricci dark energy. Regression analysis and a chi-square test were performed. A second order polynomial regression has been established as the relation between the Hubble Parameter and redshift. It has established a set of parameters that can predict the Equation of State (EoS) parameter.
Asian Journal of Research and Reviews in Physics, 2021
In this paper, we study the -gravitation theory under the assumption that the standard matter-ene... more In this paper, we study the -gravitation theory under the assumption that the standard matter-energy content of the universe is a perfect fluid with linear barotropic equation of state within the framework of Bianchi-Type III model from the class of homogeneous and anisotropic universe models. However, whether such a restriction lead to any contradictions or inconsistencies in the field equations will create an issue that needs to be examined. Under the effective fluid approach, we will be concerned mainly the field equations in an orthonormal tetrad framework with an equimolar and examined the situation of establishing the functional form of together with the scale factors, which are their solutions. Unlike similar studies, which are very few in the literature, instead of assuming preliminary solutions, we determined the consistency conditions of the field equations by assuming the matter energy content of the universe as an isotropic perfect fluid for Bianchi-Type III.
Universe, 2021
A recent work proposed that the recent cosmic passage to a cosmic acceleration era is the result ... more A recent work proposed that the recent cosmic passage to a cosmic acceleration era is the result of the existence of small anti-gravity sources in each galaxy and clusters of galaxies. In particular, a Swiss-cheese cosmology model, which relativistically integrates the contribution of all these anti-gravity sources on a galactic scale has been constructed assuming the presence of an infrared fixed point for a scale dependent cosmological constant. The derived cosmological expansion provides an explanation for both the fine tuning and the coincidence problem. The present work relaxes the previous assumption on the running of the cosmological constant and allows for a generic scaling around the infrared fixed point. Our analysis reveals that, in order to produce a cosmic evolution consistent with the best ΛCDM model, the IR-running of the cosmological constant is consistent with the presence of an IR-fixed point.
International Journal of Geometric Methods in Modern Physics, 2021
This paper examines the cosmic evolution and current expansion for flat FRW universe through gene... more This paper examines the cosmic evolution and current expansion for flat FRW universe through generalized ghost pilgrim dark energy model in [Formula: see text] gravity. For this purpose, we reconstruct the models in terms of red-shift parameter with respect to three scale factors, i.e. power-law, intermediate and a scale factor defining two unified phases. We study compatibility of reconstructed [Formula: see text] models through [Formula: see text]-[Formula: see text] planes whereas graphical analysis of squared speed of sound leads to investigate their stability. We also explore the behavior of cosmological parameters such as equation of state and deceleration parameters. Moreover, we study the existence of freezing/thawing regions via [Formula: see text]-[Formula: see text] planes. We conclude that squared speed of sound identifies both stability/instability of reconstructed [Formula: see text] models while equation of state and deceleration parameters specifies transition from d...
Motivated by the work of Saridakis (Phys. Rev. D 102, 123525 (2020)), the present study reports t... more Motivated by the work of Saridakis (Phys. Rev. D 102, 123525 (2020)), the present study reports the cosmological consequences of Barrow holographic dark energy (HDE) and its thermodynamics. Literatures demonstrate that Dark Energy (DE) may result from electroweak symmetry breaking that triggers a phase transition from early inflation to late time acceleration. In the present study, we incorporated viscosity in the Barrow HDE. A reconstruction scheme is presented for the parameters associated with Barrow holographic dark energy under the purview of viscous cosmology. Equation of state (EoS) parameter is reconstructed in this scenario and quintessence behaviour is observed. Considering Barrow HDE as a specific case of Nojiri-Odintsov (NO) HDE, we have observed quintom behaviour of the EoS parameter and for some values of n the EoS has been observed to be very close to −1 for the current universe. The generalised second law of thermodynamics has come out to be valid in all the scenario...
World Academy of Science, Engineering and Technology, International Journal of Physical and Mathematical Sciences, 2015
International Journal of Geometric Methods in Modern Physics, 2021
This paper investigates the new interior solution of stellar compact spheres in the framework of ... more This paper investigates the new interior solution of stellar compact spheres in the framework of metric [Formula: see text] gravity. In this connection, we derived the Einstein field equations for static anisotropic spherically symmetric spacetime in the mechanism of Karmakar condition. The obtained results of the field equations have been studied with well-known Starobinskian model [Formula: see text] by using three different compact stars like RXJ1856-37, [Formula: see text]-[Formula: see text], [Formula: see text]-[Formula: see text]. Moreover, the constants involved in the solution of metric potentials have been determined through smooth matching conditions between the interior geometry and exterior spacetime. Thereafter, the physical significance of the obtained results is examined in the form of fluid variables, equation of state (EoS) parameters, energy conditions, anisotropic stress and stability analysis by using the graphical plot. The approximated values of the constants ...
Asian Journal of Research and Reviews in Physics, 2021
As it is known that General Theory of Relativity does not explain the current acceleration of the... more As it is known that General Theory of Relativity does not explain the current acceleration of the universe, so there are many attempts to generalize this theory in order to explain the cosmic acceleration without introducing some dark components such as the Dark Energy. Because of the crowd of models in literature, a need to check the models according to some criteria arises. In this study, we analyze two classes of models by means of energy condition restrictions and illustrate the analysis of those classes by graphical simulations. We consider the conservative and non-conservative cases of two classes of models to perform the analysis. The results of the viability of the classes are discussed and it is found that the value of the Hubble constant has no effect on the viability of the models. Focusing on some general classes for the models, we restrict them by means of the so-called energy conditions the energy-momentum tensor on physical grounds. Besides, we find numerical values ...
Scientific Reports, 2021
We investigate Friedmann–Lamaitre–Robertson–Walker (FLRW) models with modified Chaplygin gas and ... more We investigate Friedmann–Lamaitre–Robertson–Walker (FLRW) models with modified Chaplygin gas and cosmological constant, using dynamical system methods. We assume p=(\gamma -1)\mu -\dfrac{A}{\mu ^\alpha }p=(γ−1)μ−Aμαasequationofstatewherep = ( γ - 1 ) μ - A μ α as equation of state wherep=(γ−1)μ−Aμαasequationofstatewhere\muμisthematter−energydensity,pisthepressure,μ is the matter-energy density, p is the pressure,μisthematter−energydensity,pisthepressure,\alphaαisaparameterwhichcantakeonvaluesα is a parameter which can take on valuesαisaparameterwhichcantakeonvalues0
International Journal of Mathematics and Physics, 2017
In this paper, the nonlocal nonlinear Schrödinger and Maxwell-Bloch equations are is introduced. ... more In this paper, the nonlocal nonlinear Schrödinger and Maxwell-Bloch equations are is introduced. A particular case of this system, namely the Schrödinger equation, is integrable by the inverse scattering method as shown in the work of M. Ablowitz and Z. Musslimani. Following their idea, we prove the integrability of the nonlocal nonlinear Schrödinger and Maxwell-Bloch equation using its Lax pairs. Also the Darboux transformations are constructed, and soliton solutions are obtained from different "seed" solutions using them. One-fold, twofold and N-fold determinant representations are obtained by this transformation. Moreover, soliton and solitons-like solutions, such as dynamic and topological soliton, periodic, domain walls, kink, lamp, bright and dark solitons, bright and dark rogue waves, bright and dark positons, etc., of this equation are built. In future papers, we will investigate the conservation laws of the nonlocal nonlinear Schrödinger and Maxwell-Bloch equation using the Lax pair.
International Journal of Theoretical Physics, 2015
In a recent work, it has been proposed that the recent cosmic passage to a cosmic acceleration er... more In a recent work, it has been proposed that the recent cosmic passage to a cosmic acceleration era is the result of the existence of small anti-gravity sources in each galaxy and clusters of galaxies. In particular, a swiss-cheese cosmology model which relativistically integrates the contribution of all these anti-gravity sources on galactic scale has been constructed assuming the presence of an infrared fixed point for a scale dependent cosmological constant. The derived cosmological expansion provides explanation for both the fine tuning and the coincidence problem. The present work relaxes the previous assumption on the running of the cosmological constant and allows for a generic scaling around the infrared fixed point. Our analysis reveals in order to produce a cosmic evolution consistent with the best ΛCDM model, the IR-running of the cosmological constant is consistent with the presence of an IR-fixed point.
In this paper, we investigate f(T) cosmology and find an exact solution for f which gives a Littl... more In this paper, we investigate f(T) cosmology and find an exact solution for f which gives a Little Rip cosmology. Also, considering accelerating cosmology with dark matter, the time-dependent solution is found. For these cases, by using solutions obtained from f(T) gravity we find expressions for ω and Λ defined as time functions via equivalent description in terms of inhomogeneous fluid. This puts the question: which theoretical model describes the observational cosmology?
In this paper we consider the equation of motion for<br> the F (R, T) gravity on their prop... more In this paper we consider the equation of motion for<br> the F (R, T) gravity on their property of conformal invariance. It<br> is shown that in the general case, such a theory is not conformal<br> invariant. Studied special cases for the functions v and u in which<br> can appear properties of the theory. Also we consider cosmological<br> aspects F (R, T) theory of gravity, having considered particular case<br> F (R, T) = μR+νT^2. Showed that in this case there is a nonlinear<br> dependence of the parameter equation of state from time to time,<br> which affects its evolution.
In this letter, we explore exact solutions for the<br> Horava-Lifshitz gravity. We use of a... more In this letter, we explore exact solutions for the<br> Horava-Lifshitz gravity. We use of an extension of this theory with<br> first order dynamical lapse function. The equations of motion have<br> been derived in a fully consistent scenario. We assume that there<br> are some spherically symmetric families of exact solutions of this<br> extended theory of gravity. We obtain exact solutions and investigate<br> the singularity structures of these solutions. Specially, an exact<br> solution with the regular horizon is found.
Research in Astronomy and Astrophysics, 2021
The work reported in this paper demonstrates the cosmology of f(Q) gravity and the reconstruction... more The work reported in this paper demonstrates the cosmology of f(Q) gravity and the reconstruction of various associated parameters with different versions of holographic dark energy with generalized cut-offs, where Q = 6 H 2. The Universe is considered to be filled with viscous fluid characterized by a viscous pressure Π = – 3 H ξ, where ξ = ξ 0 + ξ 1 H + ξ 2 ( H ˙ + H 2 ) and H is the Hubble parameter. Considering the power law form of expansion, we have derived the expression of f(Q) under a non-viscous holographic framework and it is then extended to viscous cosmological settings with extended generalized holographic Ricci dark energy. The forms of f(Q) for both the cases are found to be monotonically increasing functions of Q. In the viscous holographic framework, f(Q) is reconstructed as a function of cosmic time t and is found to stay at a positive level with Nojiri-Odintsov cut-off. In these cosmological settings, the slow roll parameters are computed and a scope of exit from...
Symmetry, 2021
A scheme for the generalized Chaplygin gas equation of state is shown by using the holographic Ri... more A scheme for the generalized Chaplygin gas equation of state is shown by using the holographic Ricci dark energy. Regression analysis and a chi-square test were performed. A second order polynomial regression has been established as the relation between the Hubble Parameter and redshift. It has established a set of parameters that can predict the Equation of State (EoS) parameter.
Asian Journal of Research and Reviews in Physics, 2021
In this paper, we study the -gravitation theory under the assumption that the standard matter-ene... more In this paper, we study the -gravitation theory under the assumption that the standard matter-energy content of the universe is a perfect fluid with linear barotropic equation of state within the framework of Bianchi-Type III model from the class of homogeneous and anisotropic universe models. However, whether such a restriction lead to any contradictions or inconsistencies in the field equations will create an issue that needs to be examined. Under the effective fluid approach, we will be concerned mainly the field equations in an orthonormal tetrad framework with an equimolar and examined the situation of establishing the functional form of together with the scale factors, which are their solutions. Unlike similar studies, which are very few in the literature, instead of assuming preliminary solutions, we determined the consistency conditions of the field equations by assuming the matter energy content of the universe as an isotropic perfect fluid for Bianchi-Type III.
Universe, 2021
A recent work proposed that the recent cosmic passage to a cosmic acceleration era is the result ... more A recent work proposed that the recent cosmic passage to a cosmic acceleration era is the result of the existence of small anti-gravity sources in each galaxy and clusters of galaxies. In particular, a Swiss-cheese cosmology model, which relativistically integrates the contribution of all these anti-gravity sources on a galactic scale has been constructed assuming the presence of an infrared fixed point for a scale dependent cosmological constant. The derived cosmological expansion provides an explanation for both the fine tuning and the coincidence problem. The present work relaxes the previous assumption on the running of the cosmological constant and allows for a generic scaling around the infrared fixed point. Our analysis reveals that, in order to produce a cosmic evolution consistent with the best ΛCDM model, the IR-running of the cosmological constant is consistent with the presence of an IR-fixed point.
International Journal of Geometric Methods in Modern Physics, 2021
This paper examines the cosmic evolution and current expansion for flat FRW universe through gene... more This paper examines the cosmic evolution and current expansion for flat FRW universe through generalized ghost pilgrim dark energy model in [Formula: see text] gravity. For this purpose, we reconstruct the models in terms of red-shift parameter with respect to three scale factors, i.e. power-law, intermediate and a scale factor defining two unified phases. We study compatibility of reconstructed [Formula: see text] models through [Formula: see text]-[Formula: see text] planes whereas graphical analysis of squared speed of sound leads to investigate their stability. We also explore the behavior of cosmological parameters such as equation of state and deceleration parameters. Moreover, we study the existence of freezing/thawing regions via [Formula: see text]-[Formula: see text] planes. We conclude that squared speed of sound identifies both stability/instability of reconstructed [Formula: see text] models while equation of state and deceleration parameters specifies transition from d...
Motivated by the work of Saridakis (Phys. Rev. D 102, 123525 (2020)), the present study reports t... more Motivated by the work of Saridakis (Phys. Rev. D 102, 123525 (2020)), the present study reports the cosmological consequences of Barrow holographic dark energy (HDE) and its thermodynamics. Literatures demonstrate that Dark Energy (DE) may result from electroweak symmetry breaking that triggers a phase transition from early inflation to late time acceleration. In the present study, we incorporated viscosity in the Barrow HDE. A reconstruction scheme is presented for the parameters associated with Barrow holographic dark energy under the purview of viscous cosmology. Equation of state (EoS) parameter is reconstructed in this scenario and quintessence behaviour is observed. Considering Barrow HDE as a specific case of Nojiri-Odintsov (NO) HDE, we have observed quintom behaviour of the EoS parameter and for some values of n the EoS has been observed to be very close to −1 for the current universe. The generalised second law of thermodynamics has come out to be valid in all the scenario...
World Academy of Science, Engineering and Technology, International Journal of Physical and Mathematical Sciences, 2015
International Journal of Geometric Methods in Modern Physics, 2021
This paper investigates the new interior solution of stellar compact spheres in the framework of ... more This paper investigates the new interior solution of stellar compact spheres in the framework of metric [Formula: see text] gravity. In this connection, we derived the Einstein field equations for static anisotropic spherically symmetric spacetime in the mechanism of Karmakar condition. The obtained results of the field equations have been studied with well-known Starobinskian model [Formula: see text] by using three different compact stars like RXJ1856-37, [Formula: see text]-[Formula: see text], [Formula: see text]-[Formula: see text]. Moreover, the constants involved in the solution of metric potentials have been determined through smooth matching conditions between the interior geometry and exterior spacetime. Thereafter, the physical significance of the obtained results is examined in the form of fluid variables, equation of state (EoS) parameters, energy conditions, anisotropic stress and stability analysis by using the graphical plot. The approximated values of the constants ...
Asian Journal of Research and Reviews in Physics, 2021
As it is known that General Theory of Relativity does not explain the current acceleration of the... more As it is known that General Theory of Relativity does not explain the current acceleration of the universe, so there are many attempts to generalize this theory in order to explain the cosmic acceleration without introducing some dark components such as the Dark Energy. Because of the crowd of models in literature, a need to check the models according to some criteria arises. In this study, we analyze two classes of models by means of energy condition restrictions and illustrate the analysis of those classes by graphical simulations. We consider the conservative and non-conservative cases of two classes of models to perform the analysis. The results of the viability of the classes are discussed and it is found that the value of the Hubble constant has no effect on the viability of the models. Focusing on some general classes for the models, we restrict them by means of the so-called energy conditions the energy-momentum tensor on physical grounds. Besides, we find numerical values ...
Scientific Reports, 2021
We investigate Friedmann–Lamaitre–Robertson–Walker (FLRW) models with modified Chaplygin gas and ... more We investigate Friedmann–Lamaitre–Robertson–Walker (FLRW) models with modified Chaplygin gas and cosmological constant, using dynamical system methods. We assume p=(\gamma -1)\mu -\dfrac{A}{\mu ^\alpha }p=(γ−1)μ−Aμαasequationofstatewherep = ( γ - 1 ) μ - A μ α as equation of state wherep=(γ−1)μ−Aμαasequationofstatewhere\muμisthematter−energydensity,pisthepressure,μ is the matter-energy density, p is the pressure,μisthematter−energydensity,pisthepressure,\alphaαisaparameterwhichcantakeonvaluesα is a parameter which can take on valuesαisaparameterwhichcantakeonvalues0
International Journal of Mathematics and Physics, 2017
In this paper, the nonlocal nonlinear Schrödinger and Maxwell-Bloch equations are is introduced. ... more In this paper, the nonlocal nonlinear Schrödinger and Maxwell-Bloch equations are is introduced. A particular case of this system, namely the Schrödinger equation, is integrable by the inverse scattering method as shown in the work of M. Ablowitz and Z. Musslimani. Following their idea, we prove the integrability of the nonlocal nonlinear Schrödinger and Maxwell-Bloch equation using its Lax pairs. Also the Darboux transformations are constructed, and soliton solutions are obtained from different "seed" solutions using them. One-fold, twofold and N-fold determinant representations are obtained by this transformation. Moreover, soliton and solitons-like solutions, such as dynamic and topological soliton, periodic, domain walls, kink, lamp, bright and dark solitons, bright and dark rogue waves, bright and dark positons, etc., of this equation are built. In future papers, we will investigate the conservation laws of the nonlocal nonlinear Schrödinger and Maxwell-Bloch equation using the Lax pair.
International Journal of Theoretical Physics, 2015