Unbiased constraints on the clumpiness of the Universe from standard candles

Abstract

We perform unbiased tests for the clumpiness of the Universe by confronting the Zel'dovichKantowski-Dyer-Roeder luminosity distance, which describes the effect of local inhomogeneities on the propagation of light with the observational one estimated from measurements of standard candles, i.e., type Ia supernovae (SNe Ia) and gamma-ray bursts (GRBs). Methodologically, we first determine the light-curve fitting parameters which account for distance estimation in SNe Ia observations and the luminosity/energy relations which are responsible for distance estimation of GRBs in the global fit to reconstruct the Hubble diagrams in the context of a clumpy Universe.Subsequently, these Hubble diagrams allow us to achieve unbiased constraints on the matter density parameter Ω m , as well as the clumpiness parameter η which quantifies the fraction of homogeneously distributed matter within a given light cone. At a 1σ confidence level, the constraints are Ω m = 0.34 ± 0.02 and η = 1.00 +0.00 −0.02 from the joint analysis. The results suggest that the Universe full of Friedman-Lemaître-Robertson-Walker fluid is favored by observations of standard candles with very high statistical significance. On the other hand, they may also indicate that the Zel'dovich-Kantowski-Dyer-Roeder approximation is a sufficiently accurate form to describe the effects of local homogeneity on the expanding Universe.

The effect of inhomogeneities on dark energy constraints

“…However, we stress that we do not a priori fix the cosmological parameter values as in [42], but rather we constrain it with data complementary to SN Ia distances. We also obtain more stringent constraints than [70] since we use complementary datasets that constrain Ω M very well. Using the relation between η and the fraction of DM in compact objects (f p ) [53] we find f p < 0.73 at 68% C.L., but the data are not constraining at the 95% C.L.…”

Transition redshift: new constraints from parametric and nonparametric methods

“…It is assumed that the supernova will have the same intrinsic luminosity at all redshifts provided they have identical colours, the same galactic environment and shape. This assumption is expressed through the distance estimator which can be written as [67] µ obs (α,…”

“…α and β. We fix the values of α and β according to the ΛCDM model as 0.14 and 3.14 respectively while we minimize over the parameters M and H 0 [67].…”