arXiv subjects

Onder Dunya

Publications and source records attributed to Onder Dunya.

3 recordsLinked to original sources

arXiv2023

A New Approach to Flatness, Horizon and Late-time Accelerating Expansion Problems on the basis of Mach Principle

Based on the idea that the components of a cosmological metric may be determined by the total gravitational potential of the universe, the scalar field $ϕ=1/G$ in the Jordan-Brans-Dicke (JBD) theory is introduced as evolving with the inverse square of the scale factor. Since the gravitational potential is related to the field $ϕ$ resulting from Mach's principle and depends on time due to the expansion of space, the temporal evolution of the field should be in accord with the evolution of time and space intervals in the metric tensor. For the same reason, the time dependence of the field makes these comoving intervals relative for different points on the time axis. Thus, it is shown that introduction of the cosmic gravitational potential as a time dependent scalar field proportional to $1/a^2$ may resolve the flatness, the horizon and the late-time accelerating expansion problems of the standard model of cosmology. The luminosity distance vs redshift data of Type Ia supernovae is in agreement with this approach.

gr-qc↗

arXiv2021

The Higgs Field and the Jordan Brans Dicke Cosmology

We investigate a field theoretical approach to the Jordan-Brans- Dicke (JBD) theory extended with a particular potential term on a cosmological background by starting with the motivation that the Higgs field and the scale factor of the universe are related. Based on this relation, it is possible to come up with mathematically equivalent but two different interpretations. From one point of view while the universe is static, the masses of the elementary particles change with time. The other one, which we stick with throughout the manuscript, is that while the universe is expanding, particle masses are constant. Thus, a coupled Lagrangian density of the JBD field and the scale factor (the Higgs field), which exhibit a massive particle and a linearly expanding space in zeroth order respectively, is obtained. By performing a coordinate transformation in the field space for the reduced JBD action whose kinetic part is nonlinear sigma model, the Lagrangian of two scalar fields can be written as uncoupled for the Higgs mechanism. After this transformation, as a result of spontaneous symmetry breaking, the time dependent vacuum expectation value (vev) of the Higgs field and the Higgs bosons which are the particles corresponding to quantized oscillation modes about the vacuum, are found.

gr-qc↗

arXiv2017

Gravitational Wave Solutions to Linearized Jordan-Brans-Dicke Theory on a Cosmological Background

Approximate vacuum solutions of Jordan-Brans-Dicke theory for perturbed scalar field and perturbed Robertson-Walker metric, are found. Solutions for the scale factor and the scalar field in unperturbed JBD theory are dependent on the $ω$ parameter which determines how the scalar field is coupled to geometry of space-time. After adding a metric perturbation to Robertson-Walker metric and a perturbation to the scalar field, we solved the linearized JBD equations and found the scale factor and the scalar field as $a\propto t$ and $ϕ\propto t^{-2}$ with $ω=$-3/2. The results are necessary conditions for ordinary and scalar gravitational waves to exist in the vacuum case. Despite omega is a large positive number for current solar system environment observations, this value of omega makes JBD theory conformally invariant and fits recent supernovae type Ia data. We also looked for the value of omega for the case which has nonzero spatial curvature parameter.

gr-qc↗