arXiv subjects

Hatice Özer

Publications and source records attributed to Hatice Özer.

5 recordsLinked to original sources

arXiv2026

Linearized Horndeski Theory with a Potential in the Solar System Regime

In this paper, the weak-field behavior of linearized Horndeski theory is studied, with emphasis on the role of a scalar potential with a nonvanishing minimum. In this regime, the minimum of the potential acts as an effective source of background curvature and produces a contribution similar to a cosmological constant. The analysis is restricted to the linear approximation, where nonlinear screening effects such as the Vainshtein mechanism can be consistently neglected. Within this framework, the consistency of the theory with Solar-System phenomenology in the weak-field limit is examined, and possible deviations from General Relativity depending on the model parameters are discussed. To this end, the linearized field equations for a static point mass are derived, the corresponding geodesic motion is investigated, and the resulting weak-field effects in classical Solar-System observables, including perihelion advance, light deflection, and gravitational redshift, are analyzed. The analysis further focuses on the limiting regimes of very light and very heavy scalar fields. In the very light scalar field regime, consistency with Solar System phenomenology requires sufficiently large values of the coupling parameter zeta, thereby suppressing the scalar contribution at local scales and keeping deviations from General Relativity negligible. In the very heavy scalar field regime, the scalar-mediated interaction acquires a short range and becomes dynamically suppressed, leading to weak-field predictions that are practically indistinguishable from those of General Relativity. Nevertheless, geometric terms associated with the minimum of the scalar potential may persist at linear order in the metric perturbations, depending on the value of zeta.

gr-qc↗

arXiv2025

Gravitational waves in massive Horndeski theory with a potential

We investigate gravitational waves with an arbitrary potential within the framework of linearized Horndeski theory. We show that the minimum of the potential can play the role of an effective cosmological constant in this theory, which is usually neglected in previous studies of this subject. We first determine the background geometry in this setup by solving the weak field scalar and tensorial equations of linearized Horndeski theory. The solutions of linearized weak-field wave equations, in an appropriate gauge, are then obtained perturbatively to study the propagation and interactions of gravitational waves in this background. We compare our results with different realizations of the cosmological constant in Horndeski theory to compare the role of an arbitrary scalar potential with those of vacuum energy density and a linear potential. The results show that the background curvature arising from the minimum of the scalar potential effectively mimics a cosmological constant, producing distinct redshifts in the frequency and wave number that distinguish the tensor waves from massive scalar ones. We also find that the way the cosmological constant is introduced directly influences the speed and polarization of the scalar wave.

gr-qc↗

arXiv2021

Gravitational waves in Brans-Dicke Theory with a cosmological constant

Weak field gravitational wave solutions are investigated in Brans-Dicke (BD) theory in the presence of a cosmological constant. In this setting the background geometry is not flat but asymptotically de-Sitter. We investigate the linearised field equations, and their gravitational wave solutions in a certain gauge choice. We will show that this theory leads to massless scalar waves as in original BD theory and in contrast to massive BD theory. The effects of these waves on free particles and their polarization properties are studied extensively and effects of the cosmological constant is analyzed in these phenomena in detail. The energy flux of these waves are also discussed in this background. By analyzing this flux, we obtain a critical distance where the waves cannot propagate further, which extends Cosmic no Hair Conjecture (CNC) to BD theory with a cosmological constant.

gr-qc↗

arXiv2018

Linearized modified gravity theories with a cosmological term: advance of perihelion and deflection of light

Two different ways of generalizing Einstein's general theory of relativity with a cosmological constant to Brans-Dicke type scalar-tensor theories are investigated in the linearized field approximation. In the first case a cosmological constant term is coupled to a scalar field linearly whereas in the second case an arbitrary potential plays the role of a variable cosmological term. We see that the former configuration leads to a massless scalar field whereas the latter leads to a massive scalar field. General solutions of these linearized field equations for both cases are obtained corresponding to a static point mass. Geodesics of these solutions are also presented and solar system effects such as the advance of the perihelion, deflection of light rays and gravitational redshift were discussed. In general relativity cosmological constant has no role on these phenomena. We see that for the Brans-Dicke theory the cosmological constant has also no effect on these phenomena. This is because solar system observations require very large values of the Brans-Dicke parameter and the correction terms to these phenomena becomes identical to GR for these large values of this parameter. This result is also observed for the theory with arbitrary potential if the mass of the scalar field is very light. For a very heavy scalar field, however, there is no such limit on the value of this parameter and there are ranges of this parameter where these contributions may become relevant in these scales. Galactic and intergalactic dynamics is also discussed for these theories at the latter part of the paper with similar conclusions.

gr-qc↗

arXiv2016

Modified Einstein-Gauss-Bonnet gravity: Riemann-Cartan and Pseudo-Riemannian cases

A modified Einstein-Gauss-Bonnet gravity in four dimensions where the quadratic Gauss-Bonnet term is coupled to a scalar field is considered. The field equations of the model are obtained by variational methods by making use of the constrained-first order formalism covering both pseudo-Riemannian and non-Riemannian cases. In the pseudo-Riemannian case, the Lagrange multiplier forms, which impose the vanishing torsion constraint, are eliminated in favor of the remaining fields and the resulting metric field equations are expressed in terms of the double-dual curvature 2-form. In the non-Riemannian case with torsion, the field equations are expressed in terms of the pseudo-Riemannian quantities by a perturbative scheme valid for a weak coupling constant. It is shown that, for both cases, the model admits a maximally symmetric de-Sitter solution with nontrivial scalar field. Minimal coupling of a Dirac spinor to the Gauss-Bonnet modified gravity is also discussed briefly.

gr-qc↗