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Kayoomars Karami

Kayoomars Karami

Academic rank: Professor
ORCID:
Education: PhD.
ScopusId: 22979495000
HIndex:
Faculty: Faculty of Science
Address: Department of Physics, University of Kurdistan Pasdaran St., P.O.Box: 66177-15175 Sanandaj - Iran
Phone:

Research

Title
Structure formation in clustering DBI dark energy model with constant sound speed
Type
JournalPaper
Keywords
cosmological parameters, dark energy, large scale structure of Universe
Year
2018
Journal MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
DOI
Researchers Kaveh Fahimi ، Kayoomars Karami ، somaye Asadzadeh ، Kazem Rezazadeh Sarab

Abstract

Within the framework of DBI non-canonical scalar field model of dark energy, we study the growth of dark matter perturbations in both the linear and non-linear regimes. In our DBI model, we consider the anti-de Sitter warp factor $f(\phi)=f_0\, \phi^{-4}$ with constant $f_0>0$ and assume the DBI dark energy to be clustered and its sound speed $c_s$ to be constant. In the linear regime, we use the Pseudo-Newtonian formalism to obtain the growth factor of dark matter perturbations and conclude that for smaller $c_s$ (or $\tilde{f_0} \equiv f_0 H_0^2/M_P^2$), the growth factor of dark matter is smaller for clustering DBI model compared to the homogeneous one. In the non-linear regime based on the spherical collapse model, we obtain the linear overdensity $\delta_c(z_c)$, the virial overdensity $\Delta_{\rm vir}(z_c)$, overdensity at the turn around $\zeta(z_c)$ and the rate of expansion of collapsed region $h_{\rm ta}(z)$. We point out that for the smaller $c_s$ (or $\tilde{f_0}$), the values of $\delta_c(z_c)$, $\Delta_{\rm vir}(z_c)$, $\zeta(z_c)$ and $h_{\rm ta}(z)$ in non-clustering DBI models deviate more than the $\Lambda$CDM compared to the clustering DBI models. Finally, with the help of spherical collapse parameters we calculate the relative number density of halo objects above a given mass and conclude that the differences between clustering and homogeneous DBI models are more pronounced for the higher-mass halos at high redshift.