Ertan Güdekli

Istanbul University · Department of Physics

Extended $f(R)$ theories of gravity have been investigated from the symmetry point of view. We briefly has been investigated Noether symmetry of two types of extended $f(R)$ theories: $f(R,T)$ theory, in which curvature is coupled non minimally to the trace of energy momentum tensor $T_{\mu\nu}$ and mimetic $f (R) $ gravity, a theory with a scalar...

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 - A μ α as equation of state where $$\mu$$ μ is the matter-energy density, p is the pressure, $$\alpha$$ α is a parameter whic...

Motivated by the work of Saridakis (Phys. Rev. D102, 123525 (2020)), the present study reports the cosmological consequences of Barrow holographic dark energy (HDE) and its thermodynamics. The literature demonstrates that dark energy (DE) may result from electroweak symmetry breaking that triggers a phase transition from early inflation to late-tim...

Citation: Sarkar, A.; Chattopadhyay, S.; Güdekli, E. A Regression Based Approach to the Observational Hubble Parameter Data through Holographic Chaplygin Gas. Symmetry 2021, 13, 701. https://

This paper deals with the Locally rotationally symmetric (LRS) Bianchi type-I universe model in Mimetic Gravity Theory assuming it an extended form of General Relativity Theory. It was proclaimed as a conformal transformation of the Einstein-Hilbert action from Einstein frame to Jordon frame. At the outset, we have proposed a potential function on...

In the current study, we investigate the possible existence of new wormhole solutions within f(Q) gravity by using the conformal symmetry, where Q is a non-metricity scalar. Modified versions of field equations within the scope of conformal symmetry with an anisotropic source of matter are calculated using the variational approach. We consider two...

The current study discusses the charge anisotropic stellar structures in Rastall theory. For this study, the Karmarkar condition is considered to develop the embedded solutions of compact stars. To complete this analysis, the spherically symmetric spacetime is taken and solve the resulting Rastall field equations by constraining different values of...

In this paper, we calculate a new class of wormhole solutions in the framework of teleparallel gravity. To obtain a characteristic wormhole solution, we use anisotropic matter distribution and a specific form of two dark matter profiles (URC profile and Quantum wave dark matter). As a general strategy, we create a relationship between calculated en...

In this study, we examined the horizon problem in the Bianchi type- V cosmological model. Our investigation showed that we could not obtain the solution to the horizon problem without neglecting the strong energy condi- tion. As a result, we have shown no horizon problem in our model with figures and calculations.

This paper encompassed various physically realistic models of static and spherically symmetric wormholes in extended [Formula: see text] gravitational framework by incorporating the features of non-compact matter density distribution of non-commutative geometry. For this assessment, we formulated the [Formula: see text] field equations and obtained...

In this manuscript, we develop the counterpart of Tsallis holographic dark energy (THDE) model in F(R,T) theory (where R represents Ricci scalar and T is trace of energy momentum tensor (EMT)) using the two IR-cutoffs namely Hubble horizon (HH) and Granda-Oliveros (GO). The THDE is proposed on the basis of Tsallis entropy (Tsallis and Cirto, 2013)...

Cosmic radiation is an ionizing radiation produced when primary protons and α particles from outside the solar system interact with components of the earth's atmosphere. Cosmic radiation is a general term for radiation produced by high-energy subatomic particles from outer space and, more importantly, secondary (ionizing) radiation from the sun and...

This paper is devoted to explore bouncing cosmology in [Formula: see text] modified gravity. In the background of [Formula: see text] modified theory with [Formula: see text] being Torsion scalar and [Formula: see text] being the trace of energy–momentum tensor, the Hubble parameter is considered for the isotropic, flat, and homogenous universe. Th...

The present work contains a discussion on compact stellar body that is influenced by the effect of electromagnetic fields. We have tried to discuss a solution of Einstein-Maxwell Field equation with the interpretation of Buchdahl space time type function. The interior fluid density and anisotropic pressures (tangential pressure p t and radial press...

The present work contains a discussion on compact stellar body that is influenced by the effects electromagnetic fields. We have tried to discuss a solution of Einstein-Maxwell field equation with the interpretation of Buchdahl spacetime type function. The interior fluid density and anisotropic pressures have been derived for a charged fluid of com...

In this study, we have explored an anisotropic stellar configuration by applying the Karmarkar condition in the framework of [Formula: see text] [where [Formula: see text] and [Formula: see text] stand for torsion and trace of energy–momentum tensor (EMT)] gravity. We have developed field equations of [Formula: see text] gravity for a spherically s...

Received Abstract Sixteen machine learning methods including K-Nearest-Neighbor, Random Forest, Additive Regression, Lineer Regression and M5P etc. were used to estimate the cosmic radiation dose for different international flights related with Istanbul and Ankara Airports in Turkey. Latitude, longlitude and depth were used as inputs to the develop...

In this study, we build up a general formalism for tilted N-component fluid form to investigate the isotropization features of the Bianchi-type models excluding Bianchi-IX. We applied this formalism to Bianchi type I and V models as analytically and numerically using the metric approach of Einstein field equations. It is found that only the stiff f...

As discussed in the previous section, business process modeling does not add value without further validation and analysis of the business process model. Similarly, process analysis is of little value if it does not help to improve or optimize the business process. Process improvement can occur using appropriate formal methods that support both mod...

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 cutoffs , where Q = 6H 2. The Universe is considered to be filled with viscous fluid characterized by a viscous pressure Π = −3Hξ, where ξ = ξ 0 + ξ 1...

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 accord...

In this paper, we focused on the study of anisotropic strange stars with anisotropic matter distribution in the framework of f(T,T)=αT(r)2+βT(r) model, where α, β are arbitrary constants, T and T represent the torsion scalar and trace of energy–momentum tensor, respectively. This model has interesting cosmological properties, in addition to providi...

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 contrad...

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 cons...

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...

In this work, we have studied various cosmological parameters in the presence of viscous new Tsallis holographic dark energies for interacting scenarios in the framework of Chern–Simons modified gravity. The bulk viscosity has been considered with the bulk viscous pressure chosen in the form [Formula: see text]. Hubble parameter [Formula: see text]...

In our study we are interested in dissipative gravitational collapse of anisotropic spherically symmetric radiating star satisfying initially static Karmarkar condition in formalism of f(R, T ) gravity. Moreover, we have chosen a linear model f(R, T ) = f(R) + f(T ), where R is a Ricci scalar, T is a trace of energy-momentum tensor and λ is dimensi...

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...

In the present manuscript, we have constructed an anisotropic solution for spherically symmetric space-time that satisfies Karmarkar’s condition in the context of f(R,T) theory of gravity where R and T represent the Ricci scalar and the trace of Energy-momentum tensor, respectively. In order to achieve our goal, we chose a one of the gravitational...

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 a...

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...

The purpose of this work is to present stellar models for anisotropic matter distribution in the framework of [Formula: see text] gravity with torsion scalar [Formula: see text]. In this regard, we use the interior geometry of Tolman–Kuchowicz spacetime having the potential components of the form [Formula: see text] and [Formula: see text], where [...

In this study, cosmic radiation doses were calculated for domestic and international flights departing from Istanbul and furthermore for domestic flights departing from Ankara using a software program called CARI-7A and also a mathematical method approach. Main parameters for calculating cosmic radiation are vertical cut-off rigidity, flight durati...

It is well-known that F (R) and F (T) modified gravity theories are dynamically equivalent to some scalar-tensor gravity theories. In analogy to these F (R) and F (T) modified gravity theories, it is interesting to study the conformal symmetry of the Myrzakulov gravity (MG). Note that in the MG, the curvature scalar R appearing in the gravitational...

In this study, the LRS (Local Rotational Symmetric) perfectly fluid Bianchi type - I- cosmological model is considered with the f(R,T) gravity. The particular case of f(R). f(T). The physical and kinematical properties of the model are studied. The exact solution of the field equations are obtained using the scalar expansion proportional to the she...

The coupled integrable dispersionless equations have a significant interest because of structure, integrability, and the possibility of obtaining a soliton solution. In this paper, we construct soliton surfaces for integrable dispersionless equation with self-consistent sources in Riemann space. The surfaces, arising from M-XXXII equation and their...

In this study, the LRS (Local Rotational Symmetric) perfectly fluid Bianchi type -I-cosmological model is considered with the F(R, T) gravity. The particular case of f1(R) = λ1R and f2(T) = λ2T are considered where λ1 and λ2 are real constant. [3].

In this article we study the Myrzakulov gravity with a fermion field described by a nonminimal action. The cases with a linear and nonlinear interaction of the gravitational and fermion fields are considered. It is shown that in the case of nonlinear interaction, Myrzakulov gravity can describe the accelerated expansion of the universe.

In this paper, we consider the Myrzakulov gravity (MG), that is the F (R, T) gravity, where R is the curvature scalar and T is the torsion scalar. The MG with f-essence is studied. The particular case of MG, when F (R, T) = αR + βT is considered, where α and β are some constants.

In this paper, we consider the Myrzakulov gravity with the action S37 = d 4 x √ −g[F (R, T)+Lm], where R is the curvature scalar and T is the torsion scalar. The particular case, when F (R, T) = αR + βT is studied in detail. As the matter Lagrangian Lm, we take the Myrzakulov fermionic model or accordingly to the notations of [7], the M33-model (f-...

In this paper, we investigate the dynamics of the universe on the background of f-essence when a non-minimal coupling with gravity. Field equations are obtained and using the Noether theorem, explicit forms of the coupling function and the Lagrange function of the f-essence were obtained. Accordingly, for this model, the cosmological parameters tha...

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 \(\omega\) and \(\varLambda\) defined as...

In this paper, we have investigated trace-anomaly (TA) driven inflation in Generalized Teleparallel gravity (namely f(T)). A quasi de Sitter (dS) scenario for inflation is proposed like in the case of R 2 gravity. It has been found that in f(T) gravity, the dS solution for inflation is unstable due to the conformal anomaly (CA). As an illustrative...

We have been studied the model of light Galileon with translational shift symmetry $\phi\to \phi+c$. The matter Lagrangian is presented in the form $\mathcal{L}_{\phi}= -\eta (\partial \phi)^2+\beta G^{\mu\nu}\partial_{\mu}\phi\partial_{\nu}\phi$. We have been addressed two issues: the first is that, we have been proven that, this type of Galileons...

We discuss a comprehensive description of the geometry of the brane-world cosmologies, and present bulk and brane structure and matching between brane and bulk metrics. It is clear that the possibility of the matching condition is not always obvious and therefore it requires a separate analysis. In this study we have shown, under the assumption of...