arXiv subjects

Dalibor Perkovic

Publications and source records attributed to Dalibor Perkovic.

6 recordsLinked to original sources

arXiv2024

Analytical reconstruction of equivalent purely kinetic k-essence description for $c_s^2(w)$ barotropic fluid models

A novel approach to the class of cosmic barotropic fluids in which the speed of sound squared is defined as a function of the Equation of State parameter, so called $c_s^2(w)$ models, is examined. For this class of models, a new analytical reconstruction method is introduced for finding their equivalent purely kinetic k-essence formulation. The method is explicitly demonstrated for several $c_s^2(w)$ models. A distinguished feature of the studied models is a peak in $c_s^2$ during cosmic expansion. A possible role that such model features could play in understanding of so far unexplained aspects of cosmic evolution is discussed. The application of the obtained explicit or closed form solutions in understanding dark sector unification models is outlined.

astro-ph.CO↗

arXiv2023

Dark matter fluid constraints from galaxy rotation curves

Galaxy rotation curves are considered to be convincing evidence for dark matter or some dynamically equivalent alternative mechanism. Starting only from the rotation curve data, we present a model independent approach of testing a general hypothesis that dark matter has the properties of a barotropic fluid. It is shown how the speed of sound squared can be expressed in terms of rotation curve data and their radial derivatives and how model independent constraints can be obtained from the requirements that it is confined between 0 and $c^2$. Using the Milky Way rotation curve data available in the literature, we obtain the constraints on the barotropic fluid speed of sound and illustrate the potential of this approach. Technical challenges, limitations and possible future extensions and improvements of the proposed approach are discussed.

astro-ph.CO↗

arXiv2021

Purely kinetic k-essence description of $c_s^2(w)$ barotropic fluid models

Purely kinetic k-essence models have been shown in the literature to be a field theory equivalent of barotropic fluid models of dark energy or dark matter-dark energy unification. In the modeling framework where the speed of sound squared of a barotropic fluid is modeled as a function of its Equation of State parameter, a systematic procedure of obtaining the Lagrangian density of an equivalent purely kinetic k-essence model is presented. As this modeling approach starts from the speed of sound, purely kinetic k-essence models can be constructed for which the speed of sound is in agreement with the observational constraints. Depending on the chosen functional form for the barotropic fluid speed of sound squared, analytically tractable examples of solutions for the purely kinetic k-essence Lagrangian density in parametric and closed form are obtained.

astro-ph.CO↗

arXiv2020

Barotropic fluid compatible parametrizations of dark energy

Parametrizations of Equation of state parameter as a function of the scale factor or redshift are frequently used in dark energy modeling. The question investigated in this paper is if parametrizations proposed in the literature are compatible with the dark energy being a barotropic fluid. The test of this compatibility is based on the functional form of the speed of sound squared, which for barotropic fluid dark energy follows directly from the function for the Equation of state parameter. The requirement that the speed of sound squared should be between 0 and speed of light squared provides constraints on model parameters using analytical and numerical methods. It is found that this fundamental requirement eliminates a large number of parametrizations as barotropic fluid dark energy models and puts strong constraints on parameters of other dark energy parametrizations.

gr-qc↗

arXiv2019

Dark sector unifications: dark matter-phantom energy, dark matter -- constant $w$ dark energy, dark matter-dark energy-dark matter

The paper brings a novel approach to unification of dark matter and dark energy in terms of a cosmic fluid. A model is introduced in which the cosmic fluid speed of sound squared is defined as a function of its equation of state (EoS) parameter. It is shown how logarithmic part of this function results in dynamical regimes previously not observed in cosmic fluid models. It is shown that in a particular dynamical regime the model behaves as a unification of dark matter and phantom dark energy. Further, it is shown that the model may describe dark matter - dark energy unification in which dark energy asymptotically behaves as dark energy with a constant EoS parameter larger than -1. In a specific parameter regime the unified fluid model also reproduces global expansion similar to $Λ$CDM model with fluid speed of sound vanishing for small scale factor values and being small, or even vanishing, for large scale factor values. Finally, it is shown how the model may be instrumental in describing the cosmic fluid dark matter-dark energy-dark matter unification. Physical constraints on model parameters yielding such transient dark energy behavior are obtained.

gr-qc↗

arXiv2018

Transient dark energy, cosmological constant boundary crossing and dark energy $w(z)$ data fits

The formalism of dark energy based on modeling speed of sound as a function of equation of state parameter is elaborated. A specific model which allows detailed study of cosmological constant boundary crossing is introduced and analytical solutions for the model dynamics are obtained. It is shown how in specific parameter regimes dark energy can be a transient phenomenon. It is further demonstrated how the model reproduces specific features of recent fits of dark energy $w(z)$ to observational data.

astro-ph.CO↗