We solve the equation of the equilibrium of the gravitating body, with a polytropic equation of state of the matter $P=Kρ^γ$, with $γ=1+1/n$, in the frame of the Newtonian gravity, with non-zero cosmological constant $Λ$. We consider the cases with $n=1,\,\,1.5,\,\,3$ and construct series of solutions with a fixed value of $Λ$. For each value of $n$, the non-dimensional equation of the static equilibrium has a family of solutions, instead of the unique solution of the Lane-Emden equation at $Λ=0$. The equilibrium state exists only for central densities $ρ_0$ larger than the critical value $ρ_c$. There are no static solutions at $ρ_0 < ρ_c$. We find the values of $ρ_c$ for each value of $n$ and show that the presence of dark energy decrease the dynamic stability of the configuration. We apply our results for analyzing the possibility of existence of equilibrium states for cluster of galaxies in the present universe with non-zero $Λ$.
We study the polytropic gas scenario as the unification of dark matter and dark energy. We fit the model parameters by using the latest observational data including type Ia supernovae, baryon acoustic oscillation, cosmic microwave background, and Hubble parameter data. At 68.3% and 95.4% confidence levels, we find the best fit values of the model parameters as $\tilde{K}=0.742_{-0.024}^{+0.024}(1σ)_{-0.049}^{+0.048}(2σ)$ and $n=-1.05_{-0.08}^{+0.08}(1σ)_{-0.16}^{+0.15}(2σ)$. Using the best fit values of the model, we obtain the evolutionary behaviors of the equation of state parameters of the …
Dark matter halos modeled by polytropic spheres influenced by the relict cosmological constant and trapping polytropes forming supermassive black holes
We study the primordial Universe in a cosmological model where inflation is driven by a fluid with a polytropic equation of state $p = αρ+ kρ^{1 + 1/n}$. We calculate the dynamics of the scalar factor and build a Universe with constant density at the origin. We also find the equivalent scalar field that could create such equation of state and calculate the corresponding slow-roll parameters. We calculate the scalar perturbations, the scalar power spectrum and the spectral index.
In a recent article, Kleidis and Spyrou (2015) proposed that both dark matter (DM) and dark energy (DE) can be treated as a single component, if accommodated in the context of a polytropic DM fluid with thermodynamical content. Depending only on the polytropic exponent, $-0.103 < Γ\leq 0$, this unified DM model reproduces to high accuracy the distance measurements performed with the aid of the supernovae Type Ia (SNe Ia) standard candles, without suffering either from the age or from the coincidence problem. To demonstrate also its compatibility with current observational data concerning struc…
Currently, a large amount of data implies that the matter constituents of the cosmological dark sector might be collisional. An attractive feature of such a possibility is that, it can reconcile dark matter (DM) and dark energy (DE) in terms of a single component, accommodated in the context of a polytropic-DM fluid. Accordingly, we explore the time evolution and the dynamical characteristics of a spatially-flat cosmological model, in which, in principle, there is no DE at all. Instead, in this model, the DM itself possesses some sort of fluid-like properties, i.e., the fundamental units of th…
We construct a simple model of universe with a generalized equation of state $p=(α+kρ^{1/n})ρc^2$ having a linear component $p=αρc^2$ and a polytropic component $p=kρ^{1+1/n}c^2$. For $α=1/3$, $n=1$ and $k=-4/(3ρ_P)$, where $ρ_P=5.16 10^{99} g/m^3$ is the Planck density, this equation of state provides a model of the early universe without singularity describing the transition between the pre-radiation era and the radiation era. The universe starts from $t=-\infty$ but, when $t<0$, its size is less than the Planck length $l_P=1.62 10^{-35} m$. The universe undergoes an inflationary expansion t…
We construct models of universe with a generalized equation of state $p=(αρ+kρ^{1+1/n})c^2$ having a linear component and a polytropic component. In this paper, we consider negative indices $n<0$. In that case, the polytropic component dominates in the late universe where the density is low. For $α=0$, $n=-1$ and $k=-ρ_Λ$, we obtain a model of late universe describing the transition from the matter era to the dark energy era. The universe exists eternally in the future and undergoes an inflationary expansion with the cosmological density $ρ_Λ=7.02 10^{-24} g/m^3$ on a timescale $t_Λ=1.46 10^{1…
We consider the global cosmological evolution and the evolution of the density contrast in the Bose-Einstein condensate dark matter model, in the framework of a Post-Newtonian cosmological approach. In the Bose-Einstein model, dark matter can be described as a non-relativistic, Newtonian gravitational condensate, whose density and pressure are related by a barotropic equation of state. For a condensate with quartic non-linearity, the equation of state is polytropic with index $n=1$. The basic equation describing the evolution of the perturbations of the Bose-Einstein condensate is obtained, an…
Traversable Wormholes induced by polytropic $n=1$ energy density
Università degli Studi di Bergamo（贝加莫大学）；I.N.F.N.- sezione di Milano（意大利国家核物理研究所米兰分部）；Centro de Astronomia e Astrofísica da Universidade de Lisboa（里斯本大学天文学与天体物理学中心）
We study the strong gravity regime in viable models of so-called f(R) gravity that account for the observed cosmic acceleration. In contrast with recent works suggesting that very relativistic stars might not exist in these models, we find numerical solutions corresponding to static star configurations with a strong gravitational field. The choice of the equation of state for the star is crucial for the existence of solutions. Indeed, if the pressure exceeds one third of the energy density in a large part of the star, static configurations do not exist. In our analysis, we use a polytropic equ…
The primary target for the planned space-borne gravitational wave interferometers DECIGO/BBO is a primordial gravitational wave background (PGWB). However there exist astrophysical foregrounds and among them, gravitational waves from neutron star (NS) binaries are the solid and strong component that must be identified and subtracted. In this paper, we discuss the geometry of detector configurations preferable for identifying the NS/NS binary signals. As a first step, we analytically estimate the minimum signal-to-noise ratios (SNRs) of the binaries for several static detector configurations th…
We study the evolution of the configuration entropy for different combinations of $Ω_{m0}$ and $Ω_{\Lambda0}$ in the flat $Λ$CDM universe and find that the cosmological constant plays a decisive role in controlling the dissipation of the configuration entropy. The configuration entropy dissipates at a slower rate in the models with higher value of $Ω_{\Lambda0}$. We find that the entropy rate decays to reach a minimum and then increases with time. The minimum entropy rate occurs at an earlier time for higher value of $Ω_{\Lambda0}$. We identify a prominent peak in the derivative of the entropy…
Constraining Early Dark Energy cosmological models with Big Bang Nucleosynthesis
Astronomical Institute of Romanian Academy, Cluj-Napoca Branch（罗马尼亚科学院天体物理研究所）；Babeş-Bolyai University（博拜-鲍约什大学）；Technical University of Cluj-Napoca（克卢日-纳波卡理工大学）
We introduce a new family of primordial cosmological perturbations that are not described by traditional power spectra. At the linear level, these perturbations live in the kernel of the spatial Laplacian operator, and thus we call them cosmological zero modes. We compute the cosmic microwave background (CMB) temperature and polarization anisotropy induced by these modes, and forecast their detection sensitivity using a cosmic-variance limited experiment. In particular, we consider two configurations for the zero modes: The first configuration consists of stochastic metric perturbations descri…
We present a method to extract the redshift-space distortions beta parameter in configuration space with a minimal set of cosmological assumptions. We show that a novel combination of the observed monopole and quadrupole correlation functions can remove efficiently the impact of mild non linearities and redshift errors. The method offers a series of convenient properties: it does not depend on the theoretical linear correlation function, the mean galaxy density is irrelevant, only convolutions are used, there is no explicit dependence on linear bias. Analyses based on dark matter N-body simula…
We develop a cosmological model based on a quadratic equation of state p/c^2=-(α+1){ρ^2}/{ρ_P}+αρ-(α+1)ρ_Λ (where ρ_P is the Planck density and ρ_Λ the cosmological density) "unifying" vacuum energy and dark energy in the spirit of a generalized Chaplygin gas model. For $ρ\rightarrow ρ_P$, it reduces to p=-ρc^2 leading to a phase of early accelerated expansion (early inflation) with a constant density equal to the Planck density ρ_P (vacuum energy). For $ρ_Λ\llρ\ll ρ_P$, we recover the standard linear equation of state p=αρc^2 describing radiation (α=1/3) or pressureless matter (α=0) and leadi…
