198 citations · 1.8k across the 47 of their papers we have counts for
28 papers · 1 filter
Gravitating sources with zero energy density in cosmology
Özgür Akarsu, Cihad Kıbrıs, Burcu Öztürk +1
A cosmological source can have identically zero comoving energy density and still gravitate through its pressure. This differs from an energy density passing through zero at an iso…
Reconstructing sign-switching dark energy histories: Scalar-field regularity, conditional potential comparison, and representative dynamics
Shahnawaz A. Adil, Özgür Akarsu, Mariam Bouhmadi-López +3
Phenomenologically similar sign-switching dark-energy histories need not have comparable scalar-field realizations. We reconstruct minimally coupled scalars with fixed kinetic sign…
Action-selected currents and a singular conservation closure in two-fluid energy--momentum-squared cosmology
Özgür Akarsu, Bilal Bulduk, Nihan Katırcı
In multi-fluid, matter-type gravity, the Bianchi identity constrains the divergence of the total effective stress tensor but does not, by itself, determine the currents assigned to…
Defocusing dark energy: Raychaudhuri diagnostics beyond and the phantom divide
Özgür Akarsu, Antonio De Felice, N. Merve Uzun
In general relativity, cosmic acceleration is timelike defocusing of the comoving congruence and requires a negative total active gravitational mass density, $\mathcal{M}_{\rm tot}…
k-inflation: Non-separable case meets ACT measurements
Tahere Fallahi Serish, Seyed Ali Hosseini Mansoori, Fereshteh Felegary +2
We investigate a non-separable subset of -essence in which the kinetic and potential sectors interact through an coupling, implemented via a potential-dependent prefac…
Unexplored regions in teleparallel gravity: Sign-changing dark energy density
Ozgur Akarsu, Bilal Bulduk, Antonio De Felice +2
While gravity has shown considerable potential in addressing cosmological tensions, we explore previously overlooked solution spaces that hold further promise. We examine th…
Equivalence of matter-type modified gravity theories to general relativity with nonminimal matter interaction
Özgür Akarsu, Mariam Bouhmadi-López, Nihan Katırcı +3
In this study, we first establish that gravity models incorporating matter-related terms, such as , , and , into the usu…
Relativistic binary systems in scale-independent energy-momentum squared gravity
Ozgur Akarsu, Elham Nazari, Mahmood Roshan
In this paper, we study the gravitational-wave (GW) radiation and radiative behavior of relativistic binary systems in the scale-independent energy-momentum squared gravity (EMSG).…
Weak field and slow motion limits in energy-momentum powered gravity
Ozgur Akarsu, A. Kazim Camlibel, Nihan Katirci +2
We explore the weak field and slow motion limits, Newtonian and Post-Newtonian limits, of the energy-momentum powered gravity (EMPG), viz., the energy-momentum squared gravity (EMS…
Scalar field emulator via anisotropically deformed vacuum energy: Application to dark energy
Ozgur Akarsu, Nihan Katirci, Anjan A. Sen +1
We introduce a generalization of the usual vacuum energy, called `deformed vacuum energy', which yields anisotropic pressure whilst preserving zero inertial mass density. It couple…
Weak field limit of higher dimensional massive Brans-Dicke gravity: Observational constraints
Ozgur Akarsu, Alexey Chopovsky, Valerii Shulga +2
We consider higher-dimensional massive Brans-Dicke theory with Ricci-flat internal space. The background model is perturbed by a massive gravitating source which is pressureless in…
Anisotropic massive Brans-Dicke gravity extension of the standard CDM model
Ozgur Akarsu, Nihan Katirci, Nese Ozdemir +1
We present an explicit detailed theoretical and observational investigation of an anisotropic massive Brans-Dicke (BD) gravity extension of the standard CDM model, wherein the e…
Constraint on energy-momentum squared gravity from neutron stars and its cosmological implications
Ozgur Akarsu, John D. Barrow, Sercan Çıkıntoğlu +2
Deviations from the predictions of general relativity due to energy-momentum squared gravity (EMSG) are expected to become pronounced in the high density cores of neutron stars. We…
Cosmic acceleration in dust only Universe via energy-momentum powered gravity
Ozgur Akarsu, Nihan Katirci, Suresh Kumar
We propose a modified theory of gravitation constructed by the addition of the term to the Einstein-Hilbert action, and elaborate a particular case $f(T_{μν}T^{μν…
Inflation and late time acceleration designed by Stueckelberg massive photon
Ozgur Akarsu, Metin Arik, Nihan Katirci
We present a mini review of the Stueckelberg mechanism, which was proposed to make the abelian gauge theories massive as an alternative to Higgs mechanism, within the framework of…
Anisotropic inflation with a non-minimally coupled electromagnetic field to gravity
Muzaffer Adak, Ozgur Akarsu, Tekin Dereli +1
We consider the non-minimal model of gravity in -form. We investigate a particular case of the model, for which the higher order derivatives are eliminated but the scalar…
Accelerated Expansion of the Universe in a Higher Dimensional Modified Gravity with Euler-Poincaré Terms
Ozgur Akarsu, Tekin Dereli, Neslihan Oflaz
A higher dimensional modified gravity theory with an action that includes dimensionally continued Euler-Poincaré forms up to second order in curvatures is considered. The variation…
General solution of a cosmological model induced from higher dimensions using a kinematical constraint
Ozgur Akarsu, Tekin Dereli, Nihan Katirci +1
In a recent study Akarsu and Dereli (Gen. Relativ. Gravit. 45:1211, 2013) discussed the dynamical reduction of a higher dimensional cosmological model which is augmented by a kinem…
Accelerated expansion of the Universe a la the Stueckelberg mechanism
Ozgur Akarsu, Metin Arik, Nihan Katirci +1
We investigate a cosmological model in which the Stueckelberg fields are non-minimally coupled to the scalar curvature in a gauge invariant manner. We present not only a solution t…
Accelerating anisotropic cosmologies in Brans-Dicke gravity coupled to a mass-varying vector field
Ozgur Akarsu, Tekin Dereli, Neslihan Oflaz
The field equations of Brans-Dicke gravity coupled to a mass-varying vector field are derived. Anisotropic cosmological solutions with a locally rotationally symmetric Bianchi type…
Cosmology with hybrid expansion law: scalar field reconstruction of cosmic history and observational constraints
Ozgur Akarsu, Suresh Kumar, R. Myrzakulov +2
In this paper, we consider a simple form of expansion history of Universe referred to as the hybrid expansion law - a product of power-law and exponential type of functions. The an…
Probing kinematics and fate of the Universe with linearly time-varying deceleration parameter
Ozgur Akarsu, Tekin Dereli, Suresh Kumar +1
The parametrizations and (Chevallier-Polarski-Linder parametrization) of deceleration parameter, which are linear in cosmic redshift and sca…
The Dynamical Evolution of 3-Space in a Higher Dimensional Steady State Universe
Ozgur Akarsu, Tekin Dereli
We investigate a class of cosmological solutions of Einstein's field equations in higher dimensions with a cosmological constant and an ideal fluid matter distribution as a source.…
A Comparison of the LVDP and ΛCDM Cosmological Models
Ozgur Akarsu, Tekin Dereli
We compare the cosmological kinematics obtained via our law of linearly varying deceleration parameter (LVDP) with the kinematics obtained in the ΛCDM model. We show that the LVDP…