arXiv subjects

A. Kazım Çamlıbel

Publications and source records attributed to A. Kazım Çamlıbel.

5 recordsLinked to original sources

arXiv2026

Observational Constraints on the Structure-Induced Dark Energy Model

A new phenomenological dark energy model, originally associated to the large-scale structure formation and considered as a solution to the fine-tuning and coincidence problems related to the cosmological constant, was analyzed within the framework of General Relativity in a Friedman-Robertson-Walker spacetime and its model parameters were estimated using cosmic chronometers and recent DESI data. It turns out that the proposed model can serve as an alternative evolving dark energy model with a novel equation of state function, apart from other popular propositions in the literature. Due to the form of this phenomenological energy density ansatz, which starts to rise with the nonlinear structure growth in the universe and falls with the domination of cosmic voids, we prefer to call it structure-induced dark energy. Observational constraints show that it is not only a suitable solution for the fundamental problems such as coincidence or fine-tuning problems, it gives flexibility, when considering the cosmic tensions and presents a new perspective on the evolving dark energy models.

gr-qc↗

arXiv2025

Analysis of Pantheon+ supernova data suggests evidence of sign-changing pressure of the cosmological fluid

In this work, we revisit/reinterpret/extend the model-independent analysis method (which we now call spread - luminosity distance fitting, spread-LDF) from our previous work. We apply it to the updated supernova type Ia catalogue, Pantheon+ and recent GRB compilations. The procedure allows us, using only FLRW assumption, to construct good approximations for expansion history of the universe, re-confirming its acceleration to be a robust feature. When we also assume General Relativity ("GR"), we can demonstrate, without any matter/energy model in mind, the need for (possibly nonconstant) dark energy ("GDE"). We find hints for positive pressure of GDE at z>1 with implications on either the complexity of dark energy, or the validity of one of the cosmological principle, interpretation of SN Ia data, or GR.

gr-qc↗

arXiv2025

Cosmic acceleration driven by dark matter self-interactions: a phenomenological treatment

We explore the idea that cosmic acceleration may be a byproduct of late-time effects like structure formation in two steps. First, we consider the equation of state for an inhomogeneous cosmic fluid, which may lead to a Gedanken-model for cosmic evolution, where dark matter is strongly self-interacting and stays in a plasma state until late stages of the cosmic evolution. After decoupling, it condensates to super-structures with cosmic voids similar to the current picture of the universe, introducing a negative pressure term in relation to self-interaction strength. Secondly, we carry out a cosmological analysis inspired by this scenario via a phenomenological ansatz that exhibits a transient behavior. In this analysis, we use the recent Type Ia supernova compilation and high redshift quasar data and compare the results to that of $Λ$CDM. It turns out that proposed model can solve the quasar Hubble diagram tension.

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arXiv2015

What do the cosmological supernova data really tell us?

Not much by themselves, aparently. We try to reconstruct the scale factor $a(t)$ of the universe from the SNe Ia data, i.e. the luminosity distance $d_{L}(z)$, using only the cosmological principle and the assumption that gravitation is governed by a metric theory. In our hence "model-independent," or "cosmographic" study, we fit functions to $d_{L}(z)$ rather than $a(t)$, since $d_{L}(z)$ is what is measured. We find that the acceleration history of the universe cannot be reliably determined in this approach due to the irregularity and parametrization-dependence of the results. However, adding the GRB data to the dataset cures most of the irregularities, at the cost of compromising the model-independent nature of the study slightly. Then we can determine the redshift of transition to cosmic acceleration as $z_{\rm t} \sim 0.50 \pm 0.09$ for a flat universe (larger for positive spatial curvature). If Einstein gravity (GR) is assumed, we find a redshift at which the density of the universe predicted from the $d_{L}(z)$ data is independent of curvature. We use this point to derive an upper limit on matter density, hence a lower limit on the density of dark energy. While these limits do not improve the generally accepted ones, they are derived *only using the $d_{L}(z)$ data*.

gr-qc↗

arXiv2014

Jovian planets as co-detectors of gravitational waves

Acoustic oscillations in stars can be driven by gravitational waves. However, at present it is not feasible to use the helioseismology data for their detection, since it is impossible to disentangle the uncertain driving contributions originating in the Sun itself. We here point out that any such wave will affect also Jupiter and Saturn in a similar $and$ $coordinated$ $way$; after all, they are mostly spheres of gas like the Sun, only one order of magnitude smaller. Hence, akin to the concept of coincidence detection in particle physics experiments, evaluation of the time-correlation function of the measured acoustic velocities of the same mode of oscillation of any two of these three objects will eliminate the (independent) internal effects; and observation of a peak in that correlation function will be tantamount to detection of a gravitational wave. There is a (slight) possibility that such detection has already occured.

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