Properties and uncertainties of scalar field models of dark energy with barotropic equation of state

Abstract

The dynamics of expansion and large scale structure formation in the multicomponent Universe with dark energy modeled by the minimally coupled scalar field with generalized linear barotropic equation of state (EoS) are analyzed. It is shown that the past dynamics of expansion and future of the Universe -eternal accelerated expansion or turnaround and collapse -are completely defined by the current energy density of a scalar field and relation between its current and early EoS parameters. The clustering properties of such models of dark energy and their imprints in the power spectrum of matter density perturbations depend on the same relation and, additionally, on the "effective sound speed" of a scalar field, defined by its Lagrangian. It is concluded that such scalar fields with different values of these parameters are distinguishable in principle. This gives the possibility to constrain them by confronting the theoretical predictions with the corresponding observational data. For that we have used the 7-year WMAP data on CMB anisotropies, the Union2 dataset on Supernovae Ia and SDSS DR7 data on luminous red galaxies (LRG) space distribution. Using the Markov Chain Monte Carlo technique the marginalized posterior and mean likelihood distributions are computed for the scalar fields with two different Lagrangians: Klein-Gordon and Dirac-Born-Infeld ones. The properties of such scalar field models of dark energy with best fitting parameters and uncertainties of their determination are also analyzed in the paper. PACS numbers: 95.36.+x, 98.80.-k Keywords: cosmology: dark energy-scalar field-cosmic microwave background-large scale structure of Universe-cosmological parameters

Do the cosmological observational data prefer phantom dark energy?

“…, which is interpreted as the manifestation of intrinsic entropy of the scalar field (see [20] and references therein). In the dark energy rest-frame the total pressure perturbation is expressed as δp de = c 2 s δρ de , where the effective sound speed 4 for the scalar field with given Lagrangian can be calculated as c 2 s ≡ p, X /ρ, X = L, X /(2XL, XX +L, X ), first proposed in [27].…”

“…Here as above an overdot denotes the derivative w.r.t. conformal time η. Adiabatic initial conditions for matter components can be found in [23] and the initial conditions for the early time, when the scalar field is subdominant [20] are as follows…”

“…Let us estimate the best-fit values of parameters of PSF similarly to our previous papers [20][21][22] devoted to QSF. We use the following datasets: 5. supernovae Ia luminosity distances from SDSS compilation (hereafter SN SDSS) [38], determined using the SALT2 [34] (hereafter SN SDSS SALT2) and MLCS2k2 [35] methods of light curve fitting (hereafter SN SDSS MLCS2k2).…”

Gravitational stability of dark energy in galaxies and clusters of galaxies

“…In papers [18,25,19,23,20] we analyzed the gravitational instability of the matter and dark energy in the expanding Universe and we see that obtained here analytical solutions and the results of their application to galaxies and galaxy clusters enhance greatly our understanding of properties of dark energy and its possible manifestations in the Universe.…”

Emerging the dark sector from thermodynamics of cosmological systems with constant pressure

“…The two terms, i.e. effective sound speed and adiabatic sound speed, permit one to designate dark energy intrinsic values and formally correspond to sound speed thermodynamic definitions [53]. On the contrary, assuming dark energy to evolve as a pure barotropic fluid one may infer numerical limits over the sound speed, having consequently experimental bounds useful for distinguishing an evolving dark energy model from the CDM paradigm (see for example [54]).…”