In this paper, we use an unprecedentedly large sample (158) of confirmed strong lens systems for model selection, comparing five well studied Friedmann-Robertson-Walker cosmologies: ΛCDM, wCDM (the standard model with a variable darkenergy equation of state), the R h = ct universe, the (empty) Milne cosmology, and the classical Einstein-de Sitter (matter dominated) universe. We first use these sources to optimize the parameters in the standard model and show that they are consistent with Planck, though the quality of the best fit is not satisfactory. We demonstrate that this is likely due to under-reported errors, or to errors yet to be included in this kind of analysis. We suggest that the missing dispersion may be due to scatter about a pure single isothermal sphere (SIS) model that is often assumed for the mass distribution in these lenses. We then use the Bayes information criterion, with the inclusion of a suggested SIS dispersion, to calculate the relative likelihoods and ranking of these models, showing that Milne and Einstein-de Sitter are completely ruled out, while R h = ct is preferred over ΛCDM/wCDM with a relative probability of ∼ 73% versus ∼ 24%. The recently reported sample of new strong lens candidates by the Dark Energy Survey, if confirmed, may be able to demonstrate which of these two models is favoured over the other at a level exceeding 3σ.
Measurements of the Hubble constant H(z) are increasingly being used to test the expansion rate predicted by various cosmological models. But the recent application of two-point diagnostics, such as Om(z i , z j ) and Omh 2 (z i , z j ), has produced considerable tension between CDM's predictions and several observations, with other models faring even worse. Part of this problem is attributable to the continued mixing of truly model-independent measurements using the cosmic-chronometer approach, and model-dependent data extracted from baryon acoustic oscillations. In this paper, we advance the use of two-point diagnostics beyond their current status, and introduce new variations, which we call h(z i , z j ), that are more useful for model comparisons. But we restrict our analysis exclusively to cosmic-chronometer data, which are truly model independent. Even for these measurements, however, we confirm the conclusions drawn by earlier workers that the data have strongly non-Gaussian uncertainties, requiring the use of both 'median' and 'mean' statistical approaches. Our results reveal that previous analyses using two-point diagnostics greatly underestimated the errors, thereby misinterpreting the level of tension between theoretical predictions and H(z) data. Instead, we demonstrate that as of today, only Einstein-de Sitter is ruled out by the two-point diagnostics at a level of significance exceeding ∼3σ . The R h = ct universe is slightly favoured over the remaining models, including Lambda cold dark matter and Chevalier-Polarski-Linder, though all of them (other than Einstein-de Sitter) are consistent to within 1σ with the measured mean of the h(z i , z j ) diagnostics.Key words: galaxies: distances and redshifts -galaxies: evolution -large-scale structure of Universe -cosmology: observations -cosmology: theory. I N T RO D U C T I O NLambda cold dark matter ( CDM) has done reasonably well accounting for a broad range of data and is therefore correctly viewed as the current standard model of cosmology (see, e.g. Planck Collaboration XXIII 2014). But recent analyses of the two-point correlation function of the cosmic microwave background (Melia 2014;Copi et al. 2015), as well as the Om(z i , z j ) and Omh 2 (z i , z j ) diagnostics applied to measurements of the Hubble expansion rate H(z) (Shafieloo, Sahni & Starobinsky 2012; Sahni, Shafieloo & Starobinsky 2014), appear to have revealed significant tension between its predictions and recent measurements (see, e.g. Zheng et al. 2016).In this paper, we directly address the problems highlighted by the various analyses carried out with the H(z) data, which apparently do not confirm the anticipated transition from early deceleration E-mail: kyleaf@email.arizona.edu (KL); melia@physics.arizona.eduto more recent acceleration in the cosmic expansion rate (Jimenez & Loeb 2002;Moresco et al. 2016a). With this type of work, one typically compiles a unified sample of H(z) versus redshift measurements based on various approaches, including the determination of differ...
A previous analysis of starburst-dominated HII Galaxies and HII regions has demonstrated a statistically significant preference for the Friedmann-Robertson-Walker cosmology with zero active mass, known as the R h = ct universe, over ΛCDM and its related dark-matter parametrizations. In this paper, we employ a 2-point diagnostic with these data to present a complementary statistical comparison of R h = ct with Planck ΛCDM. Our 2-point diagnostic compares-in a pairwise fashion-the difference between the distance modulus measured at two redshifts with that predicted by each cosmology. Our results support the conclusion drawn by a previous comparative analysis demonstrating that R h = ct is statistically preferred over Planck ΛCDM. But we also find that the reported errors in the HII measurements may not be purely Gaussian, perhaps due to a partial contamination by non-Gaussian systematic effects. The use of HII Galaxies and HII regions as standard candles may be improved even further with a better handling of the systematics in these sources.
We present a phenomenological method for predicting the number of Flat Spectrum Radio Quasars (FSRQs) that should be detected by upcoming Square Kilometer Array (SKA) SKA1-MID Wide Band 1 and Medium-Deep band 2 surveys. We use the Fermi Blazar Sequence and mass estimates of Fermi FSRQs, and γ-ray emitting Narrow Line Seyfert 1 galaxies, to model the radio emission of FSRQs as a function of mass alone, assuming a near-Eddington accretion rate, which is suggested by current quasar surveys at z 6. This is used to determine the smallest visible black hole mass as a function of redshift in two competing cosmologies we compare in this paper: the standard ΛCDM model and the R h = ct universe. We then apply lockstep growth to the observed black-hole mass function at z = 6 in order to devolve that population to higher redshifts and determine the number of FSRQs detectable by the SKA surveys as a function of z. We find that at the redshifts for which this method is most valid, ΛCDM predicts ∼ 30 times more FSRQs than R h = ct for the Wide survey, and ∼ 100 times more in the Medium-Deep survey. These stark differences will allow the SKA surveys to strongly differentiate between these two models, possibly rejecting one in comparison with the other at a high level of confidence.
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