Improved Constraints on the Acceleration History of the Universe and the Properties of the Dark Energy

Abstract

We extend and apply a model-independent analysis method developed earlier by Daly & Djorgovski to new samples of supernova standard candles, radio galaxy and cluster standard rulers, and use it to constrain physical properties of the dark energy as functions of redshift. Similar results are obtained for the radio galaxy and supernova data sets, which rely upon completely independent methods, suggesting that systematic errors are relatively small for both types of distances; distances to SZ clusters show a scatter which cannot be explained by the quoted measurement errors. The first and second derivatives of the distance are compared directly with predictions in a standard model based on General Relativity. The good agreement indicates that General Relativity provides an accurate description of the data on look-back time scales of about ten billion years. The first and second derivatives are combined to obtain the acceleration parameter q(z), assuming only the validity of the Robertson-Walker metric, independent of a theory of gravity and of the physical nature of the dark energy. The data are analyzed using a sliding window fit and using fits in independent

Strategies to Ascertain the Sign of the Spatial Curvature

“…It readily yields q 0 + j 0 ≥ 0. For instance, using the experimental constraint on q 0 of Daly et al [46], q 0 = −0.48 ± 0.11, we find (within 1σ)…”

“…The simple fact that, observationally, q 0 is negative [24,[46][47][48], renders j 0 positive in the said model; i.e., cosmic acceleration should be increasing nowadays.…”

Constraints on the generalized Chaplygin gas model including gamma-ray bursts via a Markov Chain Monte Carlo approach

“…Gamma-ray bursts (GRBs) have been proposed as distance indicators and regarded as a complementary cosmological probe of the universe at high redshift (Schaefer 2003;Dai et al 2004;Ghirlanda et al 2004;Firmani et al 2005Firmani et al , 2006Liang & Zhang 2005;Ghirlanda et al 2006;Schaefer 2007;Wang et al 2007;Wright 2007;Amati 2008;Basilakos & Perivolaropoulos 2008;Mosquera Cuesta et al 2008a,b;Daly et al 2008). Owing to the lack of a low-redshift sample, the empirical luminosity relations of GRBs had usually been calibrated by assuming a certain cosmological model with particular model parameters.…”

New interaction between dark energy and dark matter changes sign during cosmological evolution

“…[27]. Second, we will explore whether the model σ is consistent with the observational constraint on the position of the first peak of the cosmic microwave background power spectrum.…”