Time-independent Cosmological Constant Research Articles

Constraints on dark energy from the Ly α forest baryon acoustic oscillations measurement of the redshift 2.3 Hubble parameter

We use the Busca et al. (2012) [11] measurement of the Hubble parameter at redshift z=2.3 in conjunction with 21 lower z measurements, from Simon, Verde, and Jimenez (2005) [81], Gaztañaga, Cabré, and Hui (2009) [33], Stern et al. (2010) [85], and Moresco et al. (2012) [52], to place constraints on model parameters of constant and time-evolving dark energy cosmological models. The inclusion of the new Busca et al. (2012) [11] measurement results in H(z) constraints significantly more restrictive than those derived by Farooq, Mania, and Ratra (2013) [31]. These H(z) constraints are now more restrictive than those that follow from current Type Ia supernova (SNIa) apparent magnitude measurements Suzuki et al. (2012) [86]. The H(z) constraints by themselves require an accelerating cosmological expansion at about 2 σ confidence level, depending on cosmological model and Hubble constant prior used in the analysis. A joint analysis of H(z), baryon acoustic oscillation peak length scale, and SNIa data favors a spatially-flat cosmological model currently dominated by a time-independent cosmological constant but does not exclude slowly-evolving dark energy density.

HUBBLE PARAMETER MEASUREMENT CONSTRAINTS ON DARK ENERGY

We use 21 Hubble parameter versus redshift data points, from Gazta\~{n}aga et al. (2009), Stern et al. (2010), and Moresco et al. (2012), to place constraints on model parameters of constant and time-evolving dark energy cosmologies. This is the largest set of H(z) data considered to date. The inclusion of the 8 new Moresco et al. (2012) measurements results in H(z) constraints more restrictive than those derived by Chen & Ratra (2011b). These constraints are now almost as restrictive as those that follow from current Type Ia supernova (SNIa) apparent magnitude versus redshift data (Suzuki et al. 2012), which now more carefully account for systematic uncertainties. This is a remarkable result. We emphasize however that SNIa data have been studied for a longer time than the H(z) data, possibly resulting in a better estimate of potential systematic errors in the SNIa case. A joint analysis of the H(z), baryon acoustic oscillation peak length scale, and SNIa data favors a spatially-flat cosmological model currently dominated by a time-independent cosmological constant but does not exclude slowly-evolving dark energy.

Galaxy cluster angular-size data constraints on dark energy

We use angular size versus redshift data for galaxy clusters from Bonamente et al. (2006) to place constraints on model parameters of constant and time-evolving dark energy cosmological models. These constraints are compatible with those from other recent data, but are not very restrictive. A joint analysis of the angular size data with more restrictive baryon acoustic oscillation peak length scale and supernova Type Ia apparent magnitude data favors a spatially-flat cosmological model currently dominated by a time-independent cosmological constant but does not exclude time-varying dark energy.

Hubble parameter data constraints on dark energy

We use Hubble parameter versus redshift data from Stern et al. (2010) [1] and Gaztañaga et al. (2009) [2] to place constraints on model parameters of constant and time-evolving dark energy cosmological models. These constraints are consistent with (through not as restrictive as) those derived from supernova Type Ia magnitude-redshift data. However, they are more restrictive than those derived from galaxy cluster angular diameter distance, and comparable with those from gamma-ray burst and lookback time data. A joint analysis of the Hubble parameter data with more restrictive baryon acoustic oscillation peak length scale and supernova Type Ia apparent magnitude data favors a spatially-flat cosmological model currently dominated by a time-independent cosmological constant but does not exclude time-varying dark energy.

Constraining Dark Matter-Dark Energy Interaction with Gas Mass Fraction in Galaxy Clusters

AbstractThe recent observational evidence for the current cosmic acceleration have stimulated renewed interest in alternative cosmologies, such as scenarios with interaction in the dark sector (dark matter and dark energy). In general, such models contain an unknown negative-pressure dark component coupled with the pressureless dark matter and/or with the baryons that results in an evolution for the Universe rather different from the one predicted by the standard ΛCDM model. In this work we test the observational viability of such scenarios by using the most recent galaxy cluster gas mass fraction versus redshift data (42 X-ray luminous, dynamically relaxed galaxy clusters spanning the redshift range 0.063 < z < 1.063), Allen et al. (2008), to place bounds on the parameter ε that characterizes the dark matter/dark energy coupling. The resulting are consistent with, and typically as constraining as, those derived from other cosmological data. Although a time-independent cosmological constant (ΛCDM model) is a good fit to these galaxy cluster data, an interacting energy component cannot yet be ruled out.

CONSTRAINTS ON DARK ENERGY FROM BARYON ACOUSTIC PEAK AND GALAXY CLUSTER GAS MASS MEASUREMENTS

We use baryon acoustic peak measurements by Eisenstein et al. (2005) and Percival et al. (2007a) and galaxy cluster gas mass fraction measurements of Allen et al. (2008) to constrain parameters of three different dark energy models. For time-independent dark energy, the Percival et al. (2007a) constraints, which make use of the WMAP measurement of the apparent acoustic horizon angle, most effectively constrain a cosmological parameter close to spatial curvature and favor a close to spatially flat model. In a spatially-flat model the Percival et al. (2007a) data less effectively constrain time-varying dark energy. The joint baryon acoustic peak and galaxy cluster gas mass constraints are consistent with but tighter than those derived from other data. A time-independent cosmological constant in a spatially-flat model provides a good fit to the joint data, but slowly-evolving dark energy can not yet be ruled out.

CONSTRAINTS ON DARK ENERGY FROM THE OBSERVED EXPANSION OF OUR COSMIC HORIZON

Within the context of standard cosmology, an accelerating universe requires the presence of a third "dark" component of energy, beyond matter and radiation. The available data, however, are still deemed insufficient to distinguish between an evolving dark energy component and the simplest model of a time-independent cosmological constant. In this paper, we examine the cosmological expansion in terms of observer-dependent coordinates, in addition to the more conventional comoving coordinates. This procedure explicitly reveals the role played by the radius Rh of our cosmic horizon in the interrogation of the data. (In Rindler's notation, Rh coincides with the "event horizon" in the case of de Sitter, but changes in time for other cosmologies that also contain matter and/or radiation.) With this approach, we show that the interpretation of dark energy as a cosmological constant is clearly disfavored by the observations. Within the framework of standard Friedmann–Robertson–Walker cosmology, we derive an equation describing the evolution of Rh, and solve it using the WMAP and Type Ia supernova data. In particular, we consider the meaning of the observed equality (or near-equality) Rh(t0) ≅ ct0, where t0 is the age of the universe. This empirical result is far from trivial, for a cosmological constant would drive Rh(t) toward ct (t is the cosmic time) only once — and that would have to occur right now. Though we are not here espousing any particular alternative model of dark energy, for comparison we also consider scenarios in which dark energy is given by scaling solutions, which simultaneously eliminate several conundrums in the standard model, including the "coincidence" and "flatness" problems, and account very well for the fact that Rh(t0) ≈ ct0.

Constraints on Dark Energy from Galaxy Cluster Gas Mass Fraction versus Redshift Data

We use the Allen et al. (2008) galaxy cluster gas mass fraction versus redshift data to constrain parameters of three different dark energy models: a cosmological constant dominated one ($\Lambda$CDM); the XCDM parameterization of dark energy; and a slowly-rolling scalar field model with inverse-power-law potential energy density. (Instead of using the Monte Carlo Markov Chain method, when integrating over nuisance parameters we use an alternative method of introducing an auxiliary random variable.) The resulting constraints are consistent with, and typically more constraining than, those derived from other cosmological data. A time-independent cosmological constant is a good fit to the galaxy cluster data, but slowly evolving dark energy cannot yet be ruled out.